Physics
NAME: ________________________________________________
Unit 3
PERIOD: ____________ DATE: _________________________
Free Fall Lab
Pre-Lab Analytical Questions
Answer these questions in class with your group BEFORE performing your experiment
_____________
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1. Define acceleration. (1 pt)
2. In what three situations could an object be accelerating? (3 pts)
Part 1: Equal Spacing
3. In this lab you will listen to hex nuts tied on a string as they fall and hit a pie tin. What do
you expect to observe (hear) when you drop the equally spaced hex nuts on to the pie tin?
Explain your reasoning and be specific. (2 pts)
Part 2: Equal Timing
4. Is it possible to set up your string such that the hex nuts will hit with equal timing? If not,
why not? If so, how? Be specific. (2 pts)
Purpose: To investigate the acceleration of freely falling objects
Required Equipment and Supplies:
 5 hex nuts
 3 m of string
 meter stick/ruler
 pie tin
Discussion:
Consider a long piece of string with hex nuts tied at equally spaced intervals – say 10
centimeters apart. With the help of a balcony, hold one end of the high up, with the rest of the
string hanging vertically over the edge, directly above a pie tin on the floor below. If you drop the
string, the hex nuts will make a clanging sound as they hit the tin below. Under the influence of
gravity will the equally spaced hex nuts hit at equally spaced time intervals? A little thought
reveals that because they accelerate as they fall, the time interval between clangs decreases as the
hex nuts strike the tin.
The goal of this activity is to tie hex nuts onto a piece of string in such a way that when the
string is held vertically and dropped, the hex nuts will hit the pie tin at equal time intervals. This
experiment does not require the use of standard units of time, such as seconds or minutes. We
will simplify calculations by using the elapsed time between hex nuts hitting a tin. We call this
unit a “beat” because the sense of rhythm is used to judge whether or not the hex nuts hit the tin in
equally spaced time intervals.
Once you finish the set-up, you will be performing this experiment outside of the classroom.
PART 1: Equal Spacing
Objective: To observe the behavior of equally spaced objects in free fall.
Procedure:
1. Set Up: Use a string as long as the highest available location from which the string can be
dropped. Tie the first nut to one end of the string. Tie the remaining 5 nuts to the string
such that they are evenly spaced.
2. Take your string and pie tin out to the courtyard. Have many people carry the string to be
sure it does not tangle. This may seem simple, but you will spend about 10 minutes
untangling the string if you’re not careful!
3. Invert the pie tin on the floor so the nuts will make a clang upon impact. Hold the string so
the first nut just rests on the tin and the second is at least 10 cm above the tin. Let go and
listen to the “clangs” carefully!
PART 2: Equal Timing
Objective: to repeat the drop from part 1, but this time, manipulate your string such that you will
hear the clang of the nuts hitting the pie tin at equal time intervals.
Procedure:
1. Set Up: Use the same materials from part 1. Calculate the appropriate positions for the 4
other nuts so they strike the tin in equal time intervals.
Hint 1: The falling nuts speed up (accelerate) as they fall due to the force of gravity. Thus as
time goes on, the nuts fall a greater distance in a given time because they are going faster.
How will you compensate for this so the clangs occur at equal time intervals?
Hint 2: d = ½gt2 (for an object in free fall).
a. The distance d an object falls in time interval t is given by the equation ½gt2. The
distance is equal to a constant (½ g) multiplied by t2. The constant in your set-up is
the distance between the first two nuts. In other words, to calculate your new
spacing intervals, consider the following. Use the equation to calculate your
distances.
1. d1 = [constant] (1 s)2
2. d2 = [constant] (2 s)2
3. d3 = [constant] (3 s)2
4. d4 = [constant] (4 s)2
b. …and so on, where your constant (call it x) is the distance between the 1st and 2nd
nuts. Use this pattern to figure out what the distances between your 5 nuts should
be. Remember that d is the distance from the end of the string. Be sure to use a
constant such that all 4 intervals (between 5 nuts) will fit on your string.
2. Repeat steps 2 & 3 from part 1.
3. Show Ms. Nguyen a demonstration of your evenly-timed beats for 4 pts: ______________________
Post-Lab Questions
1. Show the calculations that allowed you to hear the beats at evenly spaced intervals for each
of the four spacings. (4 pts)
2. Regarding the motion of the hex nuts, was the velocity of the hex nuts constant throughout
their falling? Was the acceleration of the hex nuts constant throughout their falling? (2 pts)
3. At any given time (eg. t = 2.0 s), all of the nuts should have the same velocity. Why are the
time intervals between the evenly spaced nuts different? (2 pts)
4. What is the difference between the noise patterns produced by the equally-spaced nuts in
Part 1 compared to the second spacing you determined in Part 2? Explain why this
happened. (3 pts)
5. Which of the nuts had the highest velocity when hitting the pie tin? Explain. (2 pts)