Lab - Determining the Acceleration Due to Gravity for Rockville High School

Name ______Class Period______Date ______Lab Partners ______

Lab - Determining the Acceleration Due to Gravity for Our High School (HS1.1.2, HS1.4.2, HS1.4.3, HS1.6.2, H.S.1.7.4, H.S.5.1.1.6, H.S.5.1.2.4)

2 Purpose - To determine whether a motion equation presented in class d = vot + ½ at is valid Research - Keywords: NOAA.gov, gravimetry, “acceleration of gravity” , “g” , gravitational acceleration Value of “g ” for our location: Reference for research Testable Question : Can the acceleration due to gravity be determined by using a motion equation? 2 Discussion – We will be using a motion equation, d = vot + ½ at to determine the value of “g” (the acceleration due to gravity in free fall). Since there is some resistance to the free fall due to friction between the ticker timer needle and the tape present, we expect the rate of fall to be slightly less than the accepted value of –9.8 m/s2. We are expecting to get such a value using the motion equation above and known measured data for a falling body. The known data will be the measured total displacement of the dropped object, an initial drop velocity of zero, and a value for the time for the drop represented by the number of ticker tape spaces 2 (each representing 1/60 of a second). Using the equation d = vot + ½ at a value for the acceleration will be calculated and compared to the known value for “g”.

Hypothesis - If the calculated value for “g” found by using the motion equation given above is close to the expected value of –9.8 m/s2, then the motion equation is valid to use for accelerated motion.

Materials - lab table, meter stick, ticker tape, ticker tape timer, books for props, 200 gram mass, carbon paper wheels, c-clamp

Procedure - How to collect the data: . Up-end a lab table and prop up the legs with books so that the legs are parallel to the ground. . Clamp the ticker timer onto the side of the leg so that the tape will thread through the staples perpendicular to the ground, minimizing friction through the guiding staples on the timer. . Attach a 200 gram mass to a 150 cm length of ticker tape and thread the end through the timer UNDER the carbon paper. . Turn the timer on, and allow the mass to drop, dragging the tape through the timer . Label the tape as trial 1, and repeat this procedure for 4 more trials.

What data to collect: . Measure the total distance between the first clear dot and the last accelerating dot on each tape. . Count the number of spaces between these starting and finishing dots on each tape. . Record these measurements on your data table.

What to do with the data: . Calculate total time “t” for each tape run by multiplying the number of spaces by 1/60 second per space. . Calculate the acceleration “a” for each tape using vo = 0 m/s, the total distance “d” for the tape, and the 2 total time “t” for each tape. The equation you will use is: d = vot + ½ gt . Calculate the percent difference of your calculated value of “g” compared to your researched value for “g”. The equation you will use is: % Diff. = ( researched g – calculated g) 100 researched g Data Table

Trial d total (cm) d total (m) # spaces t total (sec) calculated researched % “g” (m/s2) “g” (m/s2) difference of “g” 1 2 3 4 5 ***** ***** ***** ***** average average % “g” difference

Sample Calculations Quantity Formula Used Substitution Answer / Units d (cm) to d (m)

t total (sec) “g” % Difference

Conclusions:

1. What is your answer to the testable question? Why?

2. Give three different reasons for and a brief explanation of the effect of each to tell why our classroom value for “g” was not the expected –9.8 m/s2 value.

4. Why is a negative value for “d” used in this experiment?

5. Why is the value for “g” negative when the object is gaining speed as it falls?

6. Calculate the final velocity of our falling body using the acceleration we obtained experimentally. Show your work!