A New Magdeburg Sphere the Power of Pressure SCIENTIFIC

A New Magdeburg Sphere The Power of Pressure SCIENTIFIC

Introduction Use this dramatic demonstration to illustrate the force of atmospheric pressure, the “power” of a vacuum, and to compare air and water pressure. Once the suction cups or Magdeburg hemispheres are pushed together, students will be amazed at how difficult it is to pull them apart!

Concepts • Atmospheric pressure • Magdeburg hemispheres

Materials Magdeburg hemispheres or suction cups, 2

Safety Precautions Although this activity is considered nonhazardous, please follow all normal classroom or laboratory safety guidelines.

Procedure 1. Obtain two Magdeburg hemispheres or large suction cups. 2. Press the two Magdeburg hemispheres together so they “stick” to each other. 3. Challenge one or more student volunteers to try to pull the hemispheres apart. Even your strongest student won’t be able to do it!

Disposal None required—save all materials for future use.

Tips • Magdeburg hemispheres may be purchased from Flinn Scientific, although many hardware/building supply stores sell heavy-duty suction cups used for picking up panes of glass and other large, heavy objects. Using these store- bought items can make a great “real-world” connection that intrigues students. • The force of air pressure can also be demonstrated using small plastic suction cups. Because of their small area and relatively weak seal, however, these will be easier to pull apart. Using these smaller suction cups will allow students to experimentally measure with a spring scale the force required to pull them apart. • Give students a little extra incentive to try to pull the Magdeburg hemispheres apart by placing a few dollars inside the hemispheres. Challenge the students that if they are successful in separating the hemispheres, they will be able to keep the money. • The force of atmospheric pressure can even be applied to drinking straws. By creating a suction, the pressure inside the straw is lowered, allowing the force of atmospheric pressure to push water up into the straw. Atmospheric pres sure has limits, however, in that it can only push water or liquid up about 34 ft. This makes drinking from a straw longer than 34 ft impossible.

Discussion Magdeburg hemispheres were developed by the German scientist Otto von Guericke (1602–1686) in 1650. The Magdeburg hemispheres received their name from Guericke’s hometown of Magdeburg, Germany, of which he was also the mayor. On May 8, 1654, Guericke performed a famous experiment in front of Emperor Ferdinand III in which he

© 2016 Flinn Scientific, Inc. All Rights Reserved. Publication No. 91601 1 061616 A New Magdeburg Sphere continued connected two large copper hemispheres together and used his newly invented vacuum pump to evacuate air from inside the hemispheres. He then attached a team of horses to both sides of the hemispheres and had each team pull in opposite direc- tions in an effort to separate the hemispheres. No matter how hard they tried, the horses could not pull the hemispheres apart. They were held together by the surrounding atmospheric pressure. This experiment later piqued the curiosity of Robert Boyle (1627–1691), who did further research that led him to determine the volume–pressure relationship of a gas (pressure multiplied by volume equals a constant value), later known as Boyle’s law. Earth’s atmosphere exerts a pressure on everything within it (due to the force from the rapidly moving air molecules colliding with objects within the atmosphere). At sea level, atmospheric pressure is 101,325 pascals (the SI unit of pressure), where 1 Pa is equal to 1 N/m2. Equivalent units for standard atmospheric pressure also include 1 atmosphere, 760 mm of mercury (Hg), or 14.7 pounds per square inch (lb/in2). This means that for every square inch of surface at sea level, the atmospheric molecules exert a force of 14.7 pounds. When the air is extracted or squeezed out from the inside of the Magdeburg hemispheres, air pressure inside the attached hemispheres is much lower than the air surrounding the outside of the hemispheres. Separating the hemispheres thus requires a pulling force equal to the forcing acting on the hemispheres from the unbalanced atmospheric pressure.

Connecting to the National Standards This laboratory activity relates to the following National Science Education Standards (1996): Unifying Concepts and Processes: Grades K–12 Evidence, models, and explanation Content Standards: Grades 9–12 Content Standard A: Science as Inquiry Content Standard B: Physical Science, motions and forces Content Standard G: History and Nature of Science, science as a human endeavor, historical perspectives

Flinn Scientific—Teaching Chemistry™ eLearning Video Series A video of the A New Magdeburg Sphere activity, presented by Bob Becker, is available in The Power of Pressure, part of the Flinn Scientific—Teaching Chemistry eLearning Video Series.

Materials for A New Magdeburg Sphere are available from Flinn Scientific, Inc. Catalog No. Description AP4638 Magdeburg Hemisphere AP5661 Magdeburg Hemisphere, Rubber Consult your Flinn Scientific Catalog/Reference Manual for current prices.