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Home , Gravity, Mass

Varda Bar, Yaffa Brosh, and Cary Sneider

Weight, , and : Threshold Concepts in Learning

Abstract information to fi x some of the most glar- a bright seventh grader is interviewed Threshold concepts are essential ideas ing problems. A recent step in the right before and after a class on photosynthe- about the natural that present ei- direction has been development of Next sis. Prior to the class he is asked what a ther a barrier or a gateway to a deep un- Generation Science Standards (NGSS tree is mostly made from. His response derstanding of science. , mass, Lead States, 2013) in the United States, is that it is made from soil and . and gravity are threshold concepts that but it is just that—a step. The new stan- After a six-day unit on photosynthe- underpin students’ abilities to understand dards provide clear targets for assess- sis, during which he experienced a lab important ideas in all fi elds of science, ment, but do not provide a pathway for activity coordinated with lectures on embodied in the performance expecta- reaching them. how plants extract carbon from carbon tions in the Next Generation Science In this paper, we argue that to meet dioxide in the air, and learns about the Standards (NGSS). This study begins the new standards curriculum develop- chemistry of , he was with a review of research on students’ ers and teachers must focus on help- again asked the same question. Despite diffi culties in understanding these con- ing students develop deep, fl exible, and instruction from a knowledgeable teacher, cepts individually and in relation to each useful threshold concepts that provide he again gives the same answer—that the other, based on individual interviews and the intellectual underpinnings of the material in a tree comes from soil and surveys of several hundred children that standards. To illustrate this instructional water. Although he correctly stated the illustrate how students’ understanding strategy we have chosen the concepts chemical equation for photosynthesis, of weight, mass, and gravity develops of weight, mass, and gravity, since they when asked if the wood, bark, and leaves over the lifespan, from age fi ve through are essential for grasping a number of come mostly from carbon dioxide in the adult. New data from an additional 451 performance expectations in all dis- air, he replies that is impossible because subjects in the critical age range of 10 ciplinary . While we understand air doesn’t weigh anything, stating “If to 14 years old support and extend the and support the new vision for three- it did we wouldn’t be able to breathe.” prior fi ndings. The purpose of the cur- dimensional instruction (i.e., combin- Although it may not be surprising that rent study is to provide teachers and ing practices, crosscutting concepts, seventh grade students have diffi culty curriculum developers with actionable and core ideas) implicit in the NGSS, understanding that gases have weight, and up-to-date information that educa- we claim that the need to help children the same video shows that graduates tors can use to help children at the up- grasp fundamental concepts continues from Harvard and MIT give the same per elementary, middle, and high school to be important. answer as the high school student—that levels achieve Next Generation Science The diffi culties posed by students’ in- the considerable mass of a tree could not Standards. ability to understand and differentiate the possibly have come from carbon in the concepts of weight and mass are well air. Like the seventh grader, the college Introduction known in . Klopfer, Champagne, graduates had no diffi culty memorizing Large parts of our nations’ science and Chaiklin (1992) noted that children the chemical formula for photosynthe- education systems are broken, and we enter school with initial ideas about sis, but when they really thought about have known about some of the problems certain essential “ubiquitous quanti- it, even that classic example of conserva- through educational research for de- ties” (e.g., weight, mass, and tion of mass seemed like they were get- cades (U.S. National Commission on ), and that a goal of science in- ting something (wood, bark, and leaves) Excellence in Education, 1983; Fleishman, struction is to develop the spontaneous from nothing (the air.) 2010; Martin et. al, 2012). It’s concepts into a scientifi c understand- The third threshold concept that we to bring these fi ndings to a broader au- ing of these —a goal that will describe in this paper is the mean- dience so that practitioners can use the the authors acknowledged was only ing of gravity, which also seems to be rarely achieved, even by the time stu- poorly learned at the middle school level Keywords: middle school, standards, physical dents reach college. (Kavanagh and Sneider, 2007a, 2007b), science, weight, mass, gravity In a compelling video, entitled “Lessons with misconceptions continuing into adult- from Thin Air” (Schneps & Sadler, 1997), hood. Recognizing that understanding

22 SCIENCE EDUCATOR of basic physics concepts are important climate and the interaction of falling, or being thrown upwards. This is for the study of geology, college profes- systems. also an that has been widely stud- sors Ashghar and Libarkin (2010) sur- 5-PS1-2. and graph quan- ied, but for which some questions still veyed 197 students enrolled in geology tities to provide evidence that re- remain (Agan & Sneider, 2004). courses at a mid-western university con- gardless of the type of change that The present investigation has been cerning their understanding of gravity. occurs when heating, cooling, or undertaken to provide a fi ner-grained anal- They found that only 21% had the cor- mixing substances, the total weight ysis of students’ schemas during the crit- rect scientifi c idea that gravity is a of is conserved. ical period ages 10 to 14, when students of attraction, and that very few students are expected to develop an initial scien- incorporated the concepts of attraction, The concept underpinning this perfor- tifi c understanding of gravity, weight, mass, and force into their explanations mance expectation is conservation of and mass and their interconnections. of gravity. Various students expressed weight under phase transformations, Although there is an extensive litera- the ideas that Earth’s “spin,” “magnetism,” which can be very challenging for fi fth ture on students’ understanding of these and “” caused the force of grade students (Galili & Bar, 1997), as threshold concepts, most of the studies attraction between Earth and other ob- we will discuss in our literature review. were done decades ago, so the fi ndings jects. The researchers identifi ed gravity MS-PS2-2. Plan an investigation to may not be true of today’s students. By as one of a small of important provide evidence that the change in conducting a systematic study of chil- threshold concepts that can act as bar- an object’s depends on the dren’s ideas across a broad age range riers to learning, or provide a gateway sum of the on the object and we hope to provide teachers and curricu- to deep understanding of many related the mass of the object. lum developers with the actionable and concepts. Concepts underlying this performance up-to-date information that they need to In this paper, we have chosen to focus expectation include mass, as embodied help students at the upper elementary, on weight, mass and gravity since these in ’s Laws of Motion, and also middle, and high school levels achieve terms are interrelated threshold concepts the relationship between force and mo- Next Generation Science Standards. for several of the performance expecta- tion which is subject to the common tions in the Next Generation Science misconception that gravity does not act Historical Background Standards (NGSS Lead States, 2013). on all objects, however they may be mov- In many cases the of a As the NGSS becomes widely adopted, ing. For example, many students believe child’s understanding of a concept may students will be expected to have a ro- that gravity does not act on an object that parallel the development of a concept in bust scientifi c understanding of these has been thrown upward, until it reverses the . Consequently, a concepts in order to achieve a number direction and starts to fall (Palmer, 2001). brief historical review can provide use- of performance expectations. Following ful insights for researchers by suggesting is a list of performance expectations that MS - ESS2 - 4. Develop a model the possible causes of learners’ diffi cul- require understanding of weight, mass, to describe the cycling of water ties, as well as for teachers to be aware and/or gravity. through Earth’s systems driven by of possible misconceptions that their

1 from the and the force of students may hold. Children can also 5-LS1-1. Support an argument that gravity. plants get the materials they need benefi t from accounts of scientists of the for growth chiefl y from air and Traditionally the water cycle has been distant past who may have shared some water. taught at the elementary level. Mov- of their own ideas about the world, and ing it to the middle school will make it how the scientists eventually changed If it were not for the compelling illustra- more accessible, but still challenging as their ideas as a result of new data, or new tion on the video, it might not be obvious it requires students to conserve matter ways of thinking (Bar and Zinn, 1998). that students’ understanding that gases under phase change from to gas, In the history of science, the weight have weight is essential to achieve this and to understand how solar energy and concept developed prior to any under- performance expectation. The concept is gravity act together to drive convec- standing of mass or gravity. Conceptions also central to ideas related to weather, tion currents that make the water cycle of weight known from antiquity are: possible. Plato (428-327 BC), who proposed that weight is a tendency of bodies to move 1 Each performance expectation in the 5-PS2-1. Support an argument that towards similar bodies, so that a rock NGSS is given a code. The code “5-LS” the gravitational force exerted by falls because it is attracted to other refers to fi fth grade life science. LS1 refers Earth on objects is directed down. to the fi rst core idea “From Molecules to rocks. (384-322 BC, 1952) in- Organisms: Structures and Processes.” The idea that Earth is a ball in cluded weight in his system of the world The fi nal numeral (“1”) is the fi rst per- has implications for such fundamental in which all heavy objects tended toward formance expectation for that core idea in concepts as “up” and “down” and how the center of the , which he fi fth grade. gravity acts on objects that are at rest, took to be the center of the Earth. Both

SUMMER 2016 VOL. 25, NO. 1 23 Aristotle and Plato included the idea of gravity, force, and motion, each of which candle melted. It was not until children levity or lightness, in their descriptions. have been extensively studied. A review reached age 10 that a majority of the In Aristotle’s system, objects, such of research on children’s and adults’ un- children (about 75%) understood that as fi re, tended to move upwards, away derstanding of gravity alone summarized weight was conserved during a phase from the center of the universe. A gener- the fi ndings of 62 studies on this topic change. ation later Euclid (325-265 BC) defi ned (Kavanagh & Sneider, 2007a, 2007b). A In addition to the usual conserva- weight by the process of weighing, us- fully comprehensive review of research tion questions the researchers asked the ing a balance scale. The same idea was related to weight and mass would fi ll the children which objects have weight and repeated by (287-212 BC). pages of a hefty book. We have, there- which do not. Very few of the 5-6 year- In renaissance , Galileo (1564- fore, selected studies that bear on the olds attributed any weight at all to light 1642 AD) discounted Aristotle’s idea of particular aspects of weight and mass objects, such as a feather, a cotton ball, a levity by pointing out that it led to the that are likely to impede children’s un- hair, or dust. By age 10 more of the chil- absurd idea that if you tied a one- derstanding of performance expectations dren attributed weight to light objects, object to a two-pound object, the re- in the NGSS, such as those listed in the but still only 40% attributed any weight sult would be an object weighing 1-1/2 introduction. at all to a hair, and only 10% to dust. It pounds, rather than three pounds. Al- wasn’t until age 15-16 when more than though Galileo supported Copernicus’ Weight 90% of the subjects recognized that (1543) idea that Earth revolved around The classic on children’s under- even very light objects, such as a hair or the sun, Newton’s idea of gravity had standing of weight began with Piaget dust, have weight. However, even among not yet been proposed, so Galileo had no (1929, 1972). He recognized that young 16 year-olds 17% of the students did not good explanation for how the Earth kept children associate the weight of an object think that air has weight. circling the sun, or why the didn’t with the effort to hold, , or move the fall to Earth. So even as late as Galileo’s object. Piaget also studied students’ un- Mass time, the modern concepts of mass and derstanding of conservation of weight— At the middle school level the concept gravity had not been determined. The that is, their recognition of whether the of mass is introduced by the ambiguous greatest change in the weight concept weight of an object changes if the object phrase “amount of matter.” Mass is also took place as part of the Newtonian revo- is deformed or cut into pieces (Piaget, operationally defi ned and distinguished lution. In the Principia, Newton (1687) 1929, 1972). Expanding on the earlier from weight by comparing the defi ned the force of attraction among all work, Galili and Bar (1997) conducted a of two objects by use of a balance scale. material objects as gravitation. He de- cross age study by interviewing 280 chil- Students are given the example that an fi ned weight (W) as the force of gravi- dren, ages 5 to 16, and compiling written object transported to the moon would questionnaires for an additional 225 par- tation (Fg) on a body and made a clear weigh less than on Earth, as measured by distinction between mass (m) and weight ticipants, ages 10 to 16. Like Piaget, they a scale, since the moon has only that can be expressed in a simple equa- found that the youngest children ages one sixth the amount of gravity as Earth, tion relating these two quantities to the 5-6 (Kindergarten, 1st grade) thought but the mass of the object, measured on free (g) towards the Earth: that an object was heaviest when it was a balance, would not change. in the form of a ball, and it weighed less Cheeseman and McDonough (2013) W = F = mg g when it was cut into pieces or spread in Australia found that when shown pic- out. The children expressed their under- The concept of weight as defi ned by tures of objects being compared using a standing of weight in tactile terms—the Newton was not a of a single balance, the youngest children, ages 6-7, ball-shaped object felt heavier when they object, but rather a force between two did not “trust the scale,” (p. 13) while the held it in their hand, so they believed objects (Wolf, 1968). Developing the older children in the study, ages 8-9, saw that it actually was heavier than when it formal concepts of mass and gravity the balance as providing evidence of the was reshaped or divided. It was not until was a struggle for and relative heaviness of different objects, they reached age 7-9 ( to fourth his contemporaries. So it should not be which can be taken as a rough idea of grade) that about 80% of children were surprising that it is a struggle for our mass, a conserved property of the object. able to conserve weight despite changes students. in appearance. Gravity Prior Research Although most children in the age Gravity is usually introduced to chil- Developing an appropriate research range 7-9 could conserve weight when dren as an explanation for why things fall review for this paper has been challeng- the shape of an object was changed, to the ground. Bar, Zinn, and Goldmuntz ing because the concepts of weight and Galili and Bar (1997) found that only (1994) conducted individual interviews gravity are deeply embedded in an ex- about 50% recognized that the weight of with 400 children, ages 4-13, and asked tensive conceptual ecology (Posner et a sample stayed the same when a solid them why things fall. Nearly all of their al., 1982) that includes such concepts as became a liquid, as when ice or a wax responses could be summarized in three

24 SCIENCE EDUCATOR categories: a) the object was not held; also found that many students believe they?” Kruger, Summers, and Palacio b) the object was heavy; and c) the ob- that gravity does not act on objects bur- (1990) reported similar fi ndings with ject was pulled by the attractive force of ied under the Earth, an idea consistent English elementary teachers and quoted the Earth (i.e., gravitation). As shown in with a comment from a college instruc- one who said, “He’ll fl oat off because Figure 1, at the youngest ages the great tor (personal communication) that some there isn’t any gravity. So he needs to be majority of children responded that ob- of his students thought a satellite cannot dressed in such a way so that he has a suf- jects fall because they are not held up fall into the ocean because water does fi cient weight force to hold him down.” by something. Between ages 7 and 10 not have gravity—just earth. Stein (2010) found beliefs that in order all three explanations were common. By not to fl oat an should stand on the time they reached age 13, the great Weight and Gravity on the Moon the moon or hold the ladder connected majority of children say that objects fall Given the common instructional to the space ship. One explanation given because they are pulled by the attractive method of helping students distinguish is that gravity needs air and the moon is force of the Earth (or by gravity). between weight and mass by asking stu- airless (Bar & Zinn, 1998). Palmer (2001) conducted individual dents to imagine transporting objects to Noce, Torosantucci, and Vincentini interviews of 112 students: including the moon, where they are weighed with a (1988) conducted a large-scale, cross- 56 in grade 6 (11-12 years-old) and 56 spring scale and compared on a balance, age study in Italy. Their sample of 362 in grade 10 (15-16 years old) in Aus- it is important to know how students subjects included high school students, tralia. Students were asked to identify think about such scenarios, and a num- fi rst-year university students, adults, and which objects were acted on by gravity ber of researchers have conducted such elementary teachers. The percentage of in nine different scenarios and to justify studies (, 1982; Ruggiero, et al., subjects who gave the Newtonian answer, their choices. Only 11% of the students 1985; Ameh, 1987; Noce, Torosantucci, & that the object would fall to the moon, in grade 6 and 29% of the students in Vincentini, 1988; Kruger, Summers, & increased from 4% at the middle school grade 10 correctly indicated that gravity Palacio, 1990). Typical answers to level to 35% of the adults and 50% of acted on all the objects. A common mis- questions about what would happen to students at a scientifi c high school. Most conception was that gravity only acts on an astronaut on the moon were that they of those who indicated that objects on the falling objects (where force is in the di- would fl oat away since there is no grav- moon would fl oat said that air is neces- rection of motion), but not on stationary ity on the moon, unless they were suffi - sary for gravity to act, and, since there is objects “since they are not moving.” This ciently heavy to stay down—even without no air on the moon, there is no gravity ei- fi nding is consistent with Gunstone and gravity. For example, Watts (1982) ther. This fi nding was confi rmed by Bar, Watts (1985), who found that a common quoted Louis, age 12, who said, “No, Zinn, and Goldmuntz (1994) who found misconception that force implies motion, he wouldn’t fl oat off into space because that even children who can successfully and the direction of the force is parallel most of the have… they’ve explain that weight is the force of grav- to the direction of the motion. Palmer got those sorts of heavy boots, haven’t ity on an object, and that mass does not change when an object is transported to the moon, nonetheless believe that gravity only acts on “heavy” objects. Investigations of the ideas of high school students and adults (including col- lege students and teachers) about weight, mass, and gravity found that adults have many of the same misconceptions as younger children (Tural, Akdeniz, & Alev, 2010; Gonen, 2008; Galili & Lehavi, 2003, 2006). Ashgar and Librakin’s study (2010), for example, found very little dif- ference between their college students’ ideas and those reported in the literature for young children, despite the fact that many of their subjects were geology majors.

Weight, Mass, Gravity, as Threshold Concepts Figure 1. The reasons for given by children from age 5 to age 13. (from Bar, Zinn, & The video mentioned previously, show- Goldmuntz, 1994) ing that not even graduates of Harvard

SUMMER 2016 VOL. 25, NO. 1 25 and MIT understood that plants draw and an additional 8% believed that there most of their mass from carbon in the air, is gravity “near the .” Interviews illustrates how failure to understand cer- with the same ten students after the class tain concepts in physical science can act showed that eight of the ten had consid- as a barrier to understanding concepts in erably advanced their understanding of chemistry and . But it is not the gravity. only example. Driver (1985) noted that Sneider and Ohadi (1998) conducted children’s diffi culty in conserving weight a learning study involving 539 students acted as a barrier to understanding what in grades four through eight from 18 occurs when a nail rusts or a candle burns. classrooms in 10 states, aimed at helping In a study of children’s understanding of children unravel their misconceptions the water cycle, Bar (1989) found that it about the Earth’s shape and gravity. In- was not until age 13 that children had a struction involved several sessions using suffi cient grasp of a constructivist-historical teaching strat- during a phase change to fully understand Figure 2. Illustration from Isaac Newton’s The the water cycle. egy in which students learned about how ancient philosophers thought about pat- System of the World (1728) Results of Instruction terns they observed in the sky, such as Despite the diffi culties mentioned the daily motion of the sun, moon, and Only 40% of the less advanced students above, there have been some successful , as well as phases and eclipses, and and 50% of the more advanced students efforts to teach these threshold concepts. discussed alternative models of the Earth responded “yes” to both questions. Many Bar, Sneider, and Martimbeau (1987) in space to explain these phenomena. of the students explained that weight and developed a 90-minute instructional unit They also discussed various thought ex- gravity were considerably reduced due about for sixth graders (12 years periments, such as what would happen to to the great from earth. (In fact, old) by borrowing ideas directly from a rock that fell through a hole dug all the gravity would only be reduced by about the history of science. Subjects were way through the Earth from pole to pole. 2% at the altitude of an orbiting space shut- 48 students in two classes who had pre- The fi ndings showed signifi cant gains tle.) The second most common answer ex- viously studied the and for all students on the Earth’s shape con- plained a “no” response to both questions expressed no confusion about how the cept and a basic gravity concept (down is because gravity would be far less at that planets stayed in their orbits. Interviews towards the center of the Earth.) distance, while others said there would be with ten of the students at the start of Galili (1995) and Galili and Kaplan no gravity in space. None of the students, the unit showed that 8 of the 10 believed (1996) reported the results of a written including the college students, applied the that gravity needed air to act, so there was assessment about weight and gravity pre- two weight concepts (true and apparent) no gravity in space. The unit followed sented to 34 high school students (ages that are taught in high school physics to ex- Newton’s famous illustration of a cannon 14-15), who had just studied weight and plain the situation of the astronaut in . In a recent learning study, Stein and fi ring cannonballs from a mountaintop, as gravity in elementary and middle school, illustrated in fi gure 2. Each successive Galili (2014) taught concepts of weight and 141 high school and college students shot went further and faster until one and gravitation to 141 ninth grade stu- (ages 16-22) who had taken high school cannonball fi nally achieved orbit. The dents (age 14) in an Israeli middle physics where they learned two defi ni- students began by observing the trajectory school. The instructional method was to of balls rolling off a table, then did the tions of weight: an object’s true weight, defi ne weight operationally as the force of successively faster which is the gravitational force acting on exerted by a body on a spring scale. The balls going further and faster until one the object, and apparent weight to ac- majority of students not only improved goes into orbit. The researchers helped count for situations such as an astronaut their understanding of the nature of gravi- them extend their reasoning to the Space in orbit who appears to be “weightless,” tation, and recognized that there is gravi- Shuttle and fi nally the . even though the astronaut is subject to tation in space, but also succeeded in The teacher then explained that that if Earth’s gravitational fi eld. Questions that explaining the phenomenon of free fall, there were no gravity in space, the moon students were asked included: including what happens to astronauts in- would not stay in its orbit. Therefore, An astronaut is inside a cabin of a sat- side an orbiting space station. The middle gravity cannot depend on air. ellite coasting around the earth. school students provided more accu- A written pre-test of all of the students rate qualitative responses to questions showed that prior to instruction only a. Does the gravitational force act on about weight than high school students 27% of the students believed that grav- the astronaut? who were taught using the traditional ity acted in space. After instruction 48% b. Does the astronaut have weight? method, that weight is the force due to believed that there is gravity in space, Explain your answers. gravitation.

26 SCIENCE EDUCATOR Taken together, these studies show Table 1. Schemas about gravity, weight, and mass that some progress can be made in help- ing students develop a consistent model Schema taught by science teachers Common and persistent schemas of how and where gravity acts by en- Gravity Gravity There is gravity in space. Gravity only exists on or near Earth. gaging them in observations and dis- Gravity acts on bodies whether they are Gravity needs air, thus it is missing on the cussions about what happens to objects stationery or in motion, going up or moon or in space. that fall into holes in the Earth, or that free falling. Gravity acts on falling bodies. Gravity are launched into orbit. A teacher can Gravity acts at a distance and does does not act on bodies thrown not need air. upwards or resting bodies. rely on the human capacity to develop The force of gravity diminishes gradually The strength of gravity diminishes consistent modes of thinking in help- with increases in altitude. rapidly with distance from Earth.. ing students develop an intuitive under- Weight Weight standing of how gravity acts. However, Weight is the force of gravity exerted Weight is heaviness. attempting to persuade students to give on a body. Weight is the property of a body. up the idea of weight as the property of A body has weight if it is at rest or if it is A body does not have weight if it is falling. moving, as long as it is affected A body in space is weightless. an object and instead conceptualize it as by gravity. A body does not have weight if it is at rest. a force between two objects is not only For a falling body its true weight is not the On the moon, an object will “fl oat” if it is diffi cult, it is counterproductive since the same as its apparent weight. not heavy. vision of an astronaut fl oating in a space Light matter, like gasses, have no weight. cabin reinforces the misconception that Mass Mass since the astronaut is weightless there is Mass is the amount of matter in an object, Mass is the same as weight. measured by comparing the object with no gravity in space. a known mass using a balance scale. Common Schemas that Persist over Time Purpose of the Current Study 90% said the astronaut is not affected by Piaget’s original work continues to be In order to be effective it is important gravity but that the astronaut does have a useful way to summarize a large body for teachers to have a clear understand- weight. The main justifi cation given by of work concerning children’s ideas ing of their students’ pre-instructional the students was that there is no gravity about the physical world. By interview- ideas (Bybee et. al, 2006). Consequently, in space, but that astronauts (everybody) ing children he identifi ed common ideas, they need to know what their students’ always have weight. That is, the students which he called “schemas.” The research ideas might be and what questions to indicated their that weight is the literature described above can be sum- ask. Curriculum developers must have a property of an object and is not defi ned marized by listing the schemas that re- deeper knowledge of how students’ ideas by the force of gravity. searchers have found to be common typically develop over time, since stu- In reviewing the large body of re- among children and adults. Table 1 com- dents sometimes revert to earlier ideas search on this topic (Kavanagh & Sneider, pares the schemas about gravity, weight, when confronted with novel situations 2007a, 2007b), it has occurred to us that and mass that science teachers attempt to (National Research Council, 2007). The this pair of questions (“Is it affected by teach middle students, with the schemas purpose of this study is to provide that gravity? Does it have weight?”) could that are found to be common and persist background. provide a means for probing students’ despite instruction. We have found this changing schemas for weight and grav- table to be helpful in summarizing the Method ity over a considerable age range, and fi ndings described above, and in inter- Following a well-established tradition that the same question could be varied to preting the results of the present study. of educational researchers (e.g., Piaget, provide information on how those sche- Despite the best efforts of educators to 1929, 1972), our method is to infer chil- mas changed when students were asked teach students about the important con- dren’s understanding of a concept by to consider what would happen in differ- cepts of weight and mass, few are able to asking them questions about what might ent locations (e.g., on a table, in a fall- overcome their initial idea that weight is occur in a given situation, ranging from ing elevator, in space, or on the moon) a property of an object, not a force that common everyday examples, such as an and in different conditions (i.e., falling may change as an object is transported object resting on a table, to hypothetical or stationary). to the moon or placed in orbit. Because situations, such as an object transported students tend to maintain their miscon- to the moon. Participants ceptions even after instruction, science In the 1980s, we interviewed a group Subjects in the current study were 491 teachers—not just in physics, but in all of 40 ten-year-old pupils about whether students in Israreli schools, from age 10 fi elds of science—are faced with the or not an astronaut in a satellite (Space to age 14, organized in three groups. challenge of building a deeper under- Shuttle) is affected by gravity and if the Group 1. We will consider the group standing of on shaky ground. astronaut has weight. Approximately of forty 10 year-olds interviewed in the

SUMMER 2016 VOL. 25, NO. 1 27 1980s to be Group 1. We will not analyze derived from earlier studies in which inferential statistics. We rely primarily their comments in detail here, since it was students were interviewed about their un- on percentages of students at various a small sample. We mention this group derstanding of weight and gravity. The re- ages so that it is easy to compare with primarily because they gave intriguing searcher asked the students to mark their the fi ndings of previous researchers. responses, which led to the current study. answers on the questionnaire and to ex- Concepts of Weight, Mass, and Group 2. 265 pupils in Israeli schools plain their reasoning in writing. After the Gravity Across Ages 10-14 participated: 29 5th graders (age 10) students completed the questionnaire and Findings for questions 1, 2, and 3, and 24 6th graders (age 11) in elementary their papers were collected, the researcher are shown in Table 2. Notice that the school; and 66 seventh graders (age 12), 73 led a class discussion so that students percentage of responses for the 14 year- eighth graders (age 13), and 73 ninth grad- could hear how others answered the ques- olds in Group 2 are very similar to the re- ers (age 14) in middle school. Students tions. By asking students at each grade sponses of 14 year-olds in group 3. Thus, were tested at the beginning of the school level these questions we were able to de- group 3 provides a check of reliability— year, before any additional instruction termine how students’ ideas about weight that these questions are likely to elicit about the concepts of weight and gravity. and gravity typically change over time. similar responses from students of the Students were asked to complete a written The questionnaire for Group 3 in- same age, who have been exposed to the questionnaire. This group was included cluded the same three questions, as a same curriculum. to determine how students’ understand- check on reliability. Students in Group Q1. What is the meaning of weight? ing develops over a broad age range. 3 were asked additional questions to de- At all age levels the most common an- Group 3. 186 pupils, of age 14 (ninth velop a fi ner-grained understanding of swer to the fi rst question, by a large grade) learning in Israeli schools, com- their ideas about weight and gravity in margin, was: b. “If the object is heavy pleted a questionnaire with the same various situations. or light” (average 56%). During the class questions as group 2, and with extra The questions, selected response op- discussion that followed administration questions to check the signifi cance of tions, and data from groups 2 and 3 are of the questionnaire students in all of the the answers of group 2 (of the same age), shown in Tables 2 and 3. classes gave examples of heavy objects and to expand our understanding of the and said that they are hard to hold and concepts. Findings Given the nature of the data, and our lift, in order to illustrate the meaning Instrument goal of confi rming and refi ning the re- that they attached to the word “weight.” The questionnaire for Group 2 in- sults of prior research, we use a descrip- Thus, their ideas of weight included both cluded three multiple-choice questions tive approach, rather than computing the idea of “heaviness” related to tactile

Table 2. Distribution of responses to the fi rst three questions by Groups 2 and 3*

Q1 What is the meaning of weight? 10 years 11 years 12 years 13 years 14 years 14 years** Group 2 2 2 2 2 3 N = 29 24 66 73 73 186 a. Object is big or small 0% 0% 0% 0% 0% 0% b. Object is heavy or light 72% 54% 65% 40% 49% 46% c. Force of gravity exerted on the body 10% 21% 3% 25% 29% 26% d. of matter the body contains 7% 13% 15% 16% 4% 4% e. Force exerted on the support 10% 13% 15% 19% 18% 23% Q2 If a 5 kg object is taken to the moon: 10 years 11 years 12 years 13 years 14 years 14 years a. Both weight and mass will increase 0% 3% 3% 0% 2% 1% b. Mass will not change, weight will increase 3% 3% 15% 0% 2% 2% c. Mass will not change, weight will decrease 35% 25% 46% 62% 77% 72% d. Mass and weight will decrease 62% 70% 38% 33% 19% 17% Q3. An astronaut is in a space shuttle revolving around the Earth. 10 years 11 years 12 years 13 years 14 years 14 years a. The astronaut IS infl uenced by gravity and DOES have weight. 21% 17% 24% 14% 12% 12% b. The astronaut IS infl uenced by gravity and does NOT have weight. 7% 4% 15% 21% 27% 23% c. The astronaut is NOT infl uenced by gravity and DOES have weight. 64% 48% 32% 49% 40% 41% d. The astronaut is NOT infl uenced by gravity and does NOT have weight. 0% 0% 2% 0% 2% 0% * The table does not include students who did not answer the questions. ** Data reported in the last column is from Group 3.

28 SCIENCE EDUCATOR forces—the feeling of a heavy or light Q3. An astronaut is in a space shut- The second most common choice among object. tle revolving around the Earth… First 14 year-olds, selected by 27% in Group We note that the most common re- consider the students who answer a. or 2 and 23% in Group 3, is b. that the as- sponse b. “If the object is heavy or light” b., indicating their understanding that tronaut IS infl uenced by gravity, but does is ambiguous. That is, “heaviness” could there IS gravity in space (acting on the NOT have weight. Students who made be considered a naïve notion of weight as astronaut). Only a minority of students this selection very likely hold the follow- a property of a body, somewhat similar believe that is the case. At 10 years old, ing schemas: to the more formal concept of mass, or 28% of students believe that the as- There is gravity in space (Or may be as a force exerted on a support, such as tronaut IS infl uenced by gravity. Even near the earth). the felt weight of an object when held in among the two groups of 14 year olds, the hand. This answer is consistent with only a minority believe there is gravity A body in space is weightless. the response of a substantial minority at the altitude of the space shuttle (39% Notice that very few of the youngest of students who explain that things fall and 35%). Regarding weight, the fi nd- children choose this option (7% of 10 year- “because they are heavy” (Bar, Zinn, and ings are reversed. Among students who olds and 4% of 11 year-olds). It is quite Goldmuntz,1994). It is also consistent answer a. or c., that the astronaut DOES possible that over time the students have with the commonly expressed idea that have weight, 85% of 10 year-olds believe additional opportunities to see astro- astronauts are able to walk on the moon that the astronaut has weight, in agree- nauts apparently weightless in the Space where there is no gravity because they ment with our fi ndings from Group 1. Shuttle. The more informed older stu- wear heavy shoes (Watts 1982). Without That percentage declines somewhat among dents may also have heard that gravity interviewing students it is diffi cult to tell older students, so that by age 14, only keeps the shuttle in orbit, which would which of these schemas are guiding their half of the students believe that the as- explain this response. We doubt if this responses. tronaut has weight (52% and 53%). answer relates to an operational defi ni- Q2. If a 5kg object is taken to the This is a remarkable fi nding. The idea tion of weight. The third most common moon. . . The scenario is aimed at fi nd- that a body has weight even in space is response by the 14 year-olds is choice a. ing out whether or not the participants popular among 10 year-olds, from which that the astronaut IS infl uenced by grav- recognize that weight can change but we can infer the schema “Weight is the ity and DOES have weight. Schemas that mass does not change in a world with property of a body,” which does not we can attribute to these children are: weaker gravity. The great majority of change when it goes into space. However, pupils in grades fi ve and six (ages 10 and over the next few years students learn Gravity exists in space. 11) indicated that both mass and weight that astronauts are “weightless” in space. will decrease, showing that they do not That is likely the reason why relatively Weight is the property of a body. distinguish between these two terms in few 14 year-olds believe that astronauts OR Weight is the force of gravity ex- the particular context. However, some have weight. erted on a body. students in each of these groups (35% Further information from this ques- and 25%) responded correctly that mass tion can be gathered by looking at the A science teacher who wanted stu- would stay constant while weight would specifi c responses, which combine the dents to understand that there is gravity decrease. These children may have students’ understanding of weight and in space and that weight has the New- learned the defi nition of mass at school, gravity. Of the four choices, the most tonian meaning of the force of gravity since it is included in the school curricu- common across all ages is choice c. that on an object would probably be pleased lum. They may also have learned it from the astronaut is NOT infl uenced by grav- with this answer. However, it is important television or other informal sources. ity, but DOES have weight. This was the that such answers be interpreted cautiously Students in grade seven and older (ages response given also by approximately since it is likely that at least some 12, 13, 14, 14) were more likely to an- 90% of 10 year-olds in the 1980s. In this of the students take the fi rst meaning— swer this question correctly (46%, 62%, study it was given by 64% of 10 year- that weight is the property of a body and 77% and 72% respectively). This olds and 40% of 14 year-olds in Group 2 rather than the force of gravity on a fi nding is consistent with DePierro and and 41% of the 14 year-olds in Group 3. body—since whether an object is “heavy Grafalo (2003), who used the students’ In terms of schemas, we can infer that or light” is the most common defi nition knowledge of this distinction in Socratic the students who made this selection hold given by students at all ages. dialog as a means for advancing their un- the following schema: Almost no students gave choice d. as derstanding. The conservation of mass is their answer that gravity does NOT act based on the operational defi nition that Gravity only exists on or near Earth. in space and weight is NOT infl uenced compares the two masses on the balance It does not exist on a satellite, or in by gravity. The of responses scale. For these age levels, students have space. a., b., and c., are shown in Figure 3. learned the formal distinction between The similarity in responses between mass and weight. Weight is the property of a body. the 10 year-olds in the 1980s to the

SUMMER 2016 VOL. 25, NO. 1 29 gravity to act on an object falling to the moon’s surface (50%) or in orbit (35%). These fi ndings suggest that the sche- mas “Gravity only exists on or near Earth” and “Earth is unique” are too simplistic to describe the great majority of students’ ideas. Some students may hold the schema: “Gravity exists near all large bodies in space (also the moon)” but, “Gravity does not affect bodies in orbit.” Other students may hold the schema, noted by Stein (2010) that: The moon has gravity, but it acts only on bodies that are in contact with it. In contrast, we do not fi nd the same re- lationship between location and weight for falling objects or objects at rest on a table. Combining the data in columns a. and c., we observe the pattern shown in Figure 3. Frequency of responses from Groups 2 and 3 to the question: “An astronaut is in a space Figure 5. shuttle revolving around the Earth. Does the astronaut have weight? Is the astronaut infl uenced by There is very little difference in stu- gravity?” (Data are from Table 2.) dents’ responses to whether or not an ob- ject has weight, wherever it may be. The percentage of students who said that the 10 year-olds in the current study, and the two involve stationary objects. Q8 is object has weight was 53% in orbit, 71% similarity in responses between the 14 year- about an object on the moon. on the moon, 67% in a falling elevator, olds in Groups 2 and 3 give us confi - Combing the data from the fi rst two and 86% on Earth’s surface. These fi nd- dence that these fi ndings are consistent columns for falling objects (Q3, Q4, ings suggest that nearly all 14 year-olds across grades and over time. Q5, and Q6) reveals a major difference hold the schema: “Weight is a property Where does gravity act? Further in- in where students believe such objects of a body.” This idea, which is similar formation about how students envision are acted on by gravity. This is shown in to the more formal concept of mass, and weight and gravity can be gathered from Figure 4. applies to objects in various locations the written responses to the other ques- This fi nding is not surprising in light and states of motion, seems to persist tions presented to Group 3 that consists of the many studies that have shown from about age of 8 or 9 years old, when of 186 students, all approximately 14 years most students believe there is no grav- students fi rst learn that a scale can be old. The questions and frequency of re- ity in space. However, it does show more used to compare the (or masses) sponses are shown in Table 3 and Fig- detail than prior studies. Although the of different objects, and persists through ure 4. Notice that the fi rst row of data is great majority of students (91%) under- years of schooling during which they are also displayed in Table 1. It is repeated stand that objects falling near Earth’s told that the “real” defi nition of weight is here so it can be compared with the other surface are affected by gravity, fewer the gravitational force on a body. answers from this group. The fi rst four believe that gravity acts inside a falling We asked the last two questions, to questions involve falling bodies; the last elevator (68%), and even fewer expect test Palmer’s (2001) fi nding that 34% of

Table 3. Distribution of answers to questions 3-8 by students in Group 3 (N = 186, age 14 years old)

a. Yes Gravity Yes Weight b. Yes Gravity No Weight c. No Gravity Yes Weight d. No Gravity No Weight Q3. An astronaut is in a space shuttle 12% 23% 41% 0% revolving around the Earth. Q4. An object is falling to the moon’s surface. 38% 12% 23% 22% Q5. An object is in a free falling elevator. 49% 19% 18% 5% Q6. An object is falling from a table. 63% 28% 2% 2% Q7 An object is resting on a table. 70% 5% 16% 5% Q8. An object is resting on the moon’s surface. 45% 5% 26% 17%

30 SCIENCE EDUCATOR the problem. That has been the purpose of this paper. We did not make new discoveries about students’ under- standing of these three concepts. We have shown that the problems identifi ed by previous researchers persist. We now need to turn to the question of what to do about it.

The Concept of Weight As we mentioned in the introduction to this paper, the history of science can offer insight. It is not diffi cult to see a parallel with the development of the con- cept of weight in children and the devel- opment of the weight concept in history. The fi rst ideas about weight concern how heavy something feels. For children age 5-6, a ball feels heavier than the same Figure 4. Where does gravity exist? Responses from Group 3 (age 14, N = 186) object pushed into a different shape be- cause they perceive it to be heavier on the hand. Children who are a little more students in grade 6 and 28% of students gravity, about which most students have mature can learn to conserve weight in grade 10 believed that gravity did not deeply seated misconceptions. by experimenting with a balance, fi nd- act on stationary objects. Our fi ndings ing that two lumps of clay on a balance were consistent, in that 21% of the 14 year- Discussion have the same weight, no matter how olds in our sample (9th grade) did not The educational community in the their shapes may be changed. This is the believe that gravity acted on an object United States is now faced with a new set concept of “heaviness” that is measure- resting on a table, while only 4% thought of standards that require students to think able and represents an early notion of that gravity did not act on an object fall- deeply about scientifi c issues, and to be mass. Developing the formal concepts ing from a table. However, we did not able to apply learned concepts to new of mass and gravity was a struggle for see such a difference when asking stu- situations, and in many cases, to solve Isaac Newton and his contemporaries. dents about objects on the moon—45% engineering challenges. That means it So it should not be surprising that it is a percent believed that an object falling on will no longer be suffi cient for students struggle for our students. the moon would not be acted on by grav- to parrot back learned defi nitions, such Objects that appear to weigh noth- ity, while 43% believed that an object as “weight is the force of gravity on an ing. The question of what objects have resting on the moon’s surface would not object.” They must develop a conceptu- weight and which do not is exceptionally be acted on by gravity. ally deep understanding of core ideas. important in understanding many other To sum up these fi ndings: Miscon- In this paper we have summarized a ideas in science, as suggested in the in- ceptions about gravity are widespread, considerable body of research, including troduction concerning a bright seventh and most students enter high school the fi ndings of many researchers and our grader who did not believe that the mass with the pre-Newtonian idea that grav- own recent additions, about student’s ideas of a tree could come from carbon in the ity is a special property of Earth concerning three threshold concepts— air, since air “doesn’t weigh anything.” (and in some cases only to its soil, not weight, mass, and gravity. These three Although children do not typically men- water). And, at least on Earth, whether concepts provide the intellectual un- tion lightness in the of levity as or not gravity infl uences the motion of a derpinning of many of the performance described by Plato and Aristotle, they do body depends on how that body is mov- expectations in the Next Generation Sci- have an idea that a light object has little ing. Very few students succeed in learn- ence Standards. Failure to understand or no weight at all, an idea that persists ing that weight is the force of gravity on these concepts is likely to impede stu- into high school and for many adults an object. Instead, the idea of weight as dents’ abilities to achieve performance regarding certain objects (hair, dust) “heaviness” of a body remains for most expectations. As we have shown, very and substances (water vapor, air). There students the central idea of weight. Sepa- few students have developed a deep con- are many different activities, videos, rating the concepts of mass and weight ceptual understanding of these concepts. and other instructional resources that is also challenging, especially since both The fi rst step in determining what to have been developed to help students terms are closely bound to the idea of do about the situation is to understand learn that even air has weight, and it is

SUMMER 2016 VOL. 25, NO. 1 31 students could see the light move, con- fi rming that the table acted like a spring, to oppose the force of the object. Simi- larly when students weigh an object with a spring scale they observe the effect of the object on the spring. Mass. Regarding the concept of mass, the fi ndings reported here do support the distinction between weight and mass as typically presented in middle school. We found that the percentage of students who correctly separate the two concepts when considering what happens when an object is transported to the moon, increases from 35% at age 10 to 77% at age 14. Keeping in mind common misconceptions about gravity, it is important that when present- ing the idea of mass, it is essential to also address the gravity concept at the same Figure 5. Does an object have weight? Responses from Group 3 (age 14, N = 186) time. We do not claim that students will fully understand the distinction between the two concepts by age 14, but it’s a start, essential that some collection of these and is poorly understood by students, and it’s a distinction worth making for become part of the curriculum at the up- even at the college level. learning of additional concepts at a later per elementary level, once students have Although we advocate defi ning weight time, such as the idea of density. a solid grasp of weight as the property operationally, we caution that this alone Gravity. Regarding instruction in grav- of an object that can be weighed with a will not solve the problem that many stu- ity, recall the instructional unit cited in the scale. dents have diffi culty believing that air has literature review about a 90-minute in- A proposed defi nition of weight. weight, since it is impossible to weigh structional unit concerning orbits. Based Given the widespread fi nding that across air with a spring scale. However, certain on Newton’s description of how a cannon the age spectrum it is extremely diffi - demonstrations may help students grasp could fi re a cannonball into orbit, the unit cult to change people’s that this idea. For example, the teacher can succeeded in at least doubling the number weight is anything but felt “heaviness,” “pour” carbon dioxide gas onto a burning of sixth grade children who understood we support the recommendation by oth- candle to extinguish the fl ame. Students that there is gravity in space. Such his- ers that science curricula no longer try can blow bubbles and them fl oat torical examples can be especially rich in to convince students that weight is not a on a layer of carbon dioxide gas in a bowl. suggesting instructional methods. property of an object, but rather a force Defi nitions alone do not substitute for a In the long term it will be important to due to gravity. Instead, we believe that variety of experiences with phenomena conduct further learning studies in order to weight should be defi ned operationally, and conversations in which students de- determine how best to help students learn as the result of weighing with a spring velop a rich and nuanced understanding that Earth’s gravity extends to the Moon scale (Galili, 1995; Galili & Kaplan, of these threshold concepts. and beyond, and that the Moon and planets 1996; Galili, 2012; Morrison, 1999). This Weight and Newton’s Third Law. exert their own gravitational pull on other recommendation is consistent with chil- This concept of weight can also help bodies. Students should be able to envision dren’s earlier conception of weight as students better understand Newton’s weighing an object on different planets, felt “heaviness.” With this defi nition stu- third law—that pairs of interacting ob- noting how the weight is proportional to dents will have no diffi culty understanding jects exert equal and opposite forces on the mass of the planet, and comparing the the “weightless” condition of astronauts each other. An object on a spring scale mass of two objects on different planets us- in orbit, while still being acted on by is an excellent example of such a reac- ing a balance, fi nding that mass does not gravitation. Since objects in orbit can- tion pair. In a classical example of good change, but weight does. Understanding not be weighed—that is, they cannot be physics teaching, Minstrell (1982) de- these foundational concepts is necessary weighed by a spring scale—they are in- vised a means for demonstrating that a if students are to eventually build a deep deed weightless. Thus there is no need table exerts a force on an object that rests and consistent understanding of free fall, for the distinction between true and ap- on it. He bounced a beam of light off the , and orbits— concepts that are parent weight, which is currently taught surface of a lab table so that it shone on important for all citizens to understand in in advanced high school physics courses, a wall. When he jumped on the table the the modern age.

32 SCIENCE EDUCATOR References Driver, R. (1985). Beyond appearance: The and gravity. Journal of Science Educa- Agan, L., and Sneider, C. (2004). Learning conservation of matter. In R. Driver, E. tion and Technology, 17, 70-81. about the Earth’s shape and gravity: A Guesne, and A. Tiberghien (Eds), Chil- Gunstone, R., & Watts, M. (1985). Force guide for teachers and curriculum devel- dren’s ideas in science. Milton Keynes: and motion. In R. Driver, E. Guesne, & opers. Education Review, 2, 2. Open University Press. A. Tiberghien (Eds.), Children’s ideas Ameh, C. (1987). An analysis of teachers’ Einstein, A. & Infeld, L. (1938). The evo- in science. (pp. 85-104). Milton Keynes, and their students’ views of the concept lution of physics. The University Press, UK: Open University Press. of “gravity.” Research in Science Educa- Cambridge, UK, 226-235. Iona, M. (1988). and mi- tion, 17(2), 212-219. Einstein, A. (1916/1923). The Foundation crogravity, The Physics Teacher, 26(2), Archimedes (1978). On fl oating bodies. of the general of relativity in the 72. . New York: Dover, Book II, 540, 543. Chicago: Encyclope- Kavanagh, C. & Sneider, C. (2007a). 111-164. dia Britannica. Learning about gravity I. Free fall: A Aristotle (1952). On the heavens. Book II, Euclid (1957). The book of balance. In M. guide for teachers and curriculum de- Ch. 13, 295a, b, 296a. Chicago: Ency- Clagett (Ed.), The science of mechanics velopers. The Astronomy Education Re- clopedia Britannica. in the middle ages. Oxford, UK: Oxford view, 5(2), 21-52. University Press. Asghar, A.A., Libarkin, J.C. (2010). Gravity, Kavanagh, C. & Sneider, C. (2007b). magnetism, and “down:” Non-physics Fleischman, H. L., Hopstock, P. J., Pelczar, Learning about gravity II. Trajectories college students’ conceptions of gravity. M. P., & Shelley, B. E. (2010). High- and orbits: A guide for teachers and The Science Educator, 19(1), 42-55. from PISA 2009: Performance curriculum developers. The Astronomy Bar, V. (1989). Children’s ideas about the of US 15-year-old students in reading, Education Review, 5(2), 53-102. mathematics, and science literacy in an water cycle. Science Education, 73(4), Klopfer, L.E., Champagne, A.B. & Chaiklin, 481-500. international context. National Center for Education Statistics. Retrieved from S.D. (1992). The ubiquitous quanti- Bar, V., Sneider, C., & Martimbeau, N. https://nces.ed.gov/pubsearch/pubsinfo. ties: Explorations that inform the design (1987). What research says: Is there asp?pubid=2011004 of instruction on the physical proper- gravity in space? Science and Children, ties of matter. Science Education, 76, 34(7), 38-43. Galileo, G. (1953). Dialogue concerning 597–614. the two chief world systems. Translated Bar, V., & Zinn, B. (1998). Similar frame- by Drake, S. Chicago: University of Chi- Kruger, C.J., Summers, M.K., & Palacio, works of -at-a-distance: Early cago Press. D.J. (1990). An investigation of some scientists’ and pupil’s ideas. Science English primary school teachers’ under- Education, 7(5), 471-491. Galili, I. & Kaplan, D. (1996). Students’ standing. British Educational Research operations with the concept of weight. Journal, 16(4), 383-397. Bar, V., Zinn, B., Goldmuntz, R., & Sneider, Science Education, 80(4), 457-487. C. (1994). Children’s concepts about Martin, M. O., Mullis, V.S., Foy, P, & weight and free fall. Science Education, Galili, I. & Lehavi, Y. (2003). The im- Stanco, G.M. (2012). TIMSS 2011 inter- 78(2), 149-169. portance of weightlessness and in national results in science. International teaching gravitation. American Journal Association for the Evaluation of Edu- Bybee, R.W., Taylor, J.A., Gardner, A., of Physics, 71(11), 1127-1135. Van Scotter, P., Powell, J.C., Westbrook, cational Achievement. Amsterdam: The A., & Landes, N. (2006). The BSCS 5E Galili, I. (1995). Interpretation of chil- Netherlands. Retrieved from http://tims- Instructional Model: Origins and Ef- dren’s understanding of weightlessness. sandpirls.bc.edu/timss2011/international- fectiveness: A Report Prepared for the Research in Science Education, 25(1), results-science.html 51-74. Offi ce of Science Education, National Minstrell, J. (1982). Explaining the “at Institutes of Health. Colorado Springs, Galili, I. (2012). Promotion of cultural rest” condition of an object. The Physics CO: BSCS. content knowledge through the use of Teacher, 20, 10-14. the history and philosophy of science. Cheeseman, J., & McDonough, A. (2013). National Research Council. (2007). Tak- Science & Education, 21(9), 1283-1316. Testing young children’s ideas of mass ing science to school: Learning and and . International Jour- Galili, I., & Bar, V. (1997). Children’s teaching science in grades K-8. Com- nal for Mathematics and Learning, operational knowledge about weight. mittee on Science Learning, Kinder- May, 2013. Retrieved from http://eric. International Journal of Science Educa- garten Through Eighth Grade. Duschl, ed.gov/?id=EJ1005132 tion, 19(3), 317-340. R.A., Schweingruber, H.A., and Shouse, Copernicus, N. (1543). De revolutionibus Galili, I. & Lehavi, Y. (2006). Defi nitions A.W., (Eds.). Board on Science Educa- orbium coelestium, or On the revolu- of physical concepts: A study of physics tion, Center for Education. Division of tions. Nuremberg: Johann Petreius. teachers’ knowledge and views. Inter- Behavioral and Social and Ed- DePierro, E., & Grafalo, F. (2003). Using national Journal of Science Education, ucation. Washington, DC: The National a Socratic dialog to help students con- 28(5), 521-541. Academies Press. struct fundamental concepts. Journal Gőnen, S. (2008). A study on student Morrison, R. C. (1999). Weight and grav- of Chemical Education, 80(12), 1408- teachers’ ,misconceptions and scientifi - ity: The need for consistent defi nition. 1416. cally acceptable conceptions about mass The Physics Teacher, 37, 51-52.

SUMMER 2016 VOL. 25, NO. 1 33 Newton, I. (1687/1999). Mathematical prin- Posner, J., Strike, K., Hewson, P., & Gertzog., ness. Journal of Science Education and ciples of natural philosophy. Translation W. (1982). Accommodation of a sci- Technology 19(5), 470-488. by B. Cohen & A. Whitman. Berkeley, entifi c conception: Toward a theory of United States and National Commission on CA: University of California Press. conceptual change. Science Education, Excellence in Education (1983) A nation NGSS Lead States. (2013). Next generation 66(2), 211-227. at risk: The imperative for educational science standards: For states, by states, Ruggiero, S. Cartelli, A., Dupre, F., & reform: a report to the Nation and the Volume 1 The standards. Washington, Vincentini-Missoni, M. (1985). Weight, Secretary of Education, United States DC: The National Academies Press. gravity, and air : Mental rep- Department of Education, Washington, D.C.: National Commission on Excel- Noce, G., Toroscantucci, G., & Vincentini, resentations by Italian middle school lence in Education : Supt. of Docs., U.S. M. (1988). The fl oating of objects on the pupils. European Journal of Science G.P.O. distributor. moon: from a theory or ex- Education, 7(12), 181. perimental facts? International Journal Schneps, M.H., & Sadler, P.M. (1997). Watts, D. (1982) Gravity–don’t take it for of Science Education, 10(1), 61-70. Lessons from thin air. In the series granted! , 17(4), 116. Palmer, D. (2001). Students’ alternative Minds of our Own. Cambridge: Harvard- Wolf, A. (1968). A history of science, tech- conceptions and scientifi cally accept- Smithsonian Center for Astrophysics nology, and philosophy in the 16th and able conceptions about gravity. Inter- and Annenberg/CPB. 17th centuries. Gloucester, MA: Smith. national Journal of Science Education, Sneider, C., & Ohadi, M. (1998). Unravel- Varda Bar, Professor Emeritus, The He- 23(7), 691-706. ing students’ misconceptions about the brew University, Jerusalem, Israel Earth’s shape and gravity. Science Edu- Piaget, J. (1929). The child’s conception of Yaffa Brosh, PhD, The Hebrew Univer- cation, 82(2), 265-84. the world. New York: Harcourt Brace. sity, Jerusalem, Israel Stein, H. (2010). Instruction of weight and Piaget, J. (1972). The child’s conception of Cary Sneider, PhD, Associate Research gravity, PhD Thesis, Hebrew University physical . London: Routledge Professor, Portland State University, Port- & Kegan. of Jerusalem, Jerusalem, Israel. land, Oregon. Correspondence concern- Plato (1952). The dialogues of Plato. Tural, G., Akdeniz, A.R. & Alev, N. (2010). ing this article should be sent to: Dr. Cary Timaeus (Chicago: Encyclopedia Effect of 5E teaching model on student Sneider, 3834 SE Steele St., Portland, OR Britannica) 63, 463. teachers’ understanding of weightless- 97202. Email: [email protected]

34 SCIENCE EDUCATOR