AP Physics B
Unit 1: Lab Exercise - Freefall
A student conducts an experiment with the goal of determining the acceleration g due
to gravity from the data. The equipment includes a small steel sphere that is held by
an apparatus above a recording plate, as shown. When the ball is released, a timer
automatically begins recording the time of fall. The timer automatically stops when the
sphere strikes the recording plate. The student measures the time of fall for different
values of distance D shown above and records the data in the table below.
Distance of Fall (m) Time of Fall (s)
0.10
0.14
0.50
0.33
0.80
0.41
1.00
0.46
1.40
0.54
1.70
0.59
0.63
2.00
63 below. Be sure the label each
(a) Draw a graph of Distance D versus time t on the grid
axis with units. Sketch the smooth curve that best represents the student's data.
(b) What evidence can you cite to justify to statement that the steel ball is in fact
accelerating as it falls?
(c) Can the smooth curve be used by itself to calculate the experimental value of g? Why
or why not?
The student can use these data for distance D and time t to produce a second graph
from which the acceleration g due to gravity can be determined.
(d) If only the variables D and t are used, what quantities should the student graph in
order to produce a linear relationship between the two quantities?
On the grid below, plot the data points for the quantities you have identified in part (d),
and draw a best straight-line fit of the points. Label your axes and show the scale that
you have chosen for the graph.
(e) Using the slope of your graph in part (c), calculate the acceleration g due to gravity
in this experiment.
(f) Is the acceleration of the steel ball significantly changing for different trials (i.e., as D
changes)? Cite evidence to justify your answer.
(g) State one way in which the student could improve the accuracy of the results if the
experiment were to be performed again. Explain why this would improve the accuracy.
(h) The experiment is repeated but the steel ball is replaced with a lighter plastic ball.
Air resistance now has a greater effect on its motion. On your D vs time graph, sketch
your predicted smooth fit of the data for the second experiment. Use a different color
ink and label your curve. Justify the shape of the curve you drew qualitatively, not
with calculations or equations.
*Air drag is a force that opposes the motion of an object. The strength of drag force is
proportional to speed squared.