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)
Purpose - To determine whether a motion equation presented in class d = vot + ½ at2 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?
Discussion – We will be using a motion equation, d = vot + ½ at2 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
(each representing 1/60 of a second). Using the equation d = vot + ½ at2 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.
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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
total time “t” for each tape. The equation you will use is: d = vot + ½ gt2
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)
1
2
3
4
5
*****
*****
*****
*****
average
“g”
Sample Calculations
Quantity
d (cm) to d (m)
t total (sec)
“g”
% Difference
Formula Used
calculated
“g” (m/s2)
Substitution
researched
“g” (m/s2)
%
difference
of “g”
average %
difference
Answer / Units
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.
a.
b.
c.
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!