Phy 101: Fundamentals of Physics I
Instructor: Tony Zable, Ph.D.
1
Laboratory: Free Fall & Projectile Motion
Introduction:
In this assignment, you will compare one- and two-dimensional falling motion using
video motion analysis.
Objectives:
 To perform video motion analysis on a one object system
 To observe the free fall motion of a basketball
 To study the projectile motion of a basketball
 To explore how free fall and projectile motions are similar
Materials:


a digital camera & tripod
a basketball

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LoggerPro Software
a meter stick
Preliminary Questions:
1. When an object is in “free fall”, by how much does its velocity change for every
second it is in the air?
2. Recalling to Newton’s 1st Law, how does an object’s state of motion (velocity) change
when there is no (net) force acting on it?
3. If a car moving at constant velocity were to suddenly run off a cliff (no grade), would
you expect its horizontal velocity to change while it is in the air? Why or why not?
4. If a car moving at constant velocity were to suddenly run off a cliff (no grade), would
you expect its vertical velocity to change while it is in the air? Why or why not?
Phy 101: Fundamentals of Physics I
Instructor: Tony Zable, Ph.D.
2
Part 1: Free Fall
1. Obtain a basketball
2. Hold the basketball about 2 m above the ground
3. While recording with a digital camera, drop the basketball. Stop recording when the
ball hits the ground. Be sure to include a “reference object” such as a meter stick in
the field of view for scaling the movie.
4. Review the movie in the camera. If it is acceptable then upload the movie file to your
assigned computer, place it on the “desktop” for easy access
5. Start the LoggerPro software and open the “PHY101-VideoFreeFallAnalysis.cmbl”
experiment file
6. Double click on the movie window then use Browse to locate your movie. Click “OK”
to insert your movie into the experiment.
7. Resize and move the movie field (if necessary) for viewability and convenience
8. Use the QuickTime buttons to review the movie
a. Select the ball position in each frame during the fall
b. Scale movie using the “reference” object
c. Set origin to the ground at the bottom of the ball drop
Graphical analysis of free fall motion
8. Scale movie to a convenient object (such as a meter stick) then set the origin point to
the bottom of the ball’s drop.
9. Select points for the ball for each frame during its descent.
10.Observe the two graphs on the right side of the computer screen. The top graph is
the “Y” position vs time graph for the falling ball. The lower graph is the “Y” velocity
vs time graph for the ball.
11.Use the software to calculate the slope of the velocity-time graph (when the ball is in
the air). Drag the mouse across the region of the graph that represents the drop of
the ball then click on the “Linear Fit” button.
12. Print both graphs (on the same page if possible)
Slope of Velocity-Time Graph:
(don’t forget the units)
Question A: Describe the position vs. time graph. Be specific.
Question B: Describe the velocity vs. time graph. Be specific.
Phy 101: Fundamentals of Physics I
Instructor: Tony Zable, Ph.D.
3
Part 2: Rolling a Ball off a Tabletop – Projectile Motion
1. In this experiment, you will roll the basketball off the counter-top and video record its
motion as it rolls off the table and then falls to the floor.
a. Place basketball on tabletop about ½ m from the edge
b. Be sure a meter stick is in the field of view of the camera
c. When the cameraman and the experimenter(s) are ready, start recording then
give the ball a push toward the edge so that the ball falls off the table
d. Stop recording when the ball hits the ground
e. Review the movie in the camera. If it is acceptable then upload the movie file
to your assigned computer, place it on the “desktop” for easy access
2. Video Motion Analysis:
a. Using LoggerPro, re-open the “PHY101-VideoFreeFallAnalysis.cmbl” experiment
file.
b. Place your new movie into the video analysis window by double clicking on the
movie window then locate it using the “Browse” feature.
c. Perform the same video analysis procedure as described above for the free fall
basketball:
o
Scale the movie
o
Set the origin
o
Select the basketball frame-by-frame.
d. Observe the vertical position-time and velocity-time graphs.
e. Use the software to calculate the slope of the velocity-time graph (when the
ball is in the air).
f. Print both graphs (on the same page if possible)
Slope of Vertical Velocity-Time Graph:
(don’t forget the units)
Question C: How does the vertical position vs. time graph compare with the vertical
position vs. time graph for free fall (above)? Be as specific as possible.
Question D: How does the vertical velocity vs. time graph compare with the vertical
velocity vs. time graph for free fall (above)? Be as specific as possible.
Phy 101: Fundamentals of Physics I
Instructor: Tony Zable, Ph.D.
4
g. Set-up and view graphs of x-component of position and velocity for the
basketball. To do this, click on the y-axis label of the upper graph and select
“X”. Then, click on the y-axis label of the lower graph and select “X Velocity”
h. Observe the horizontal position-time and velocity-time graphs.
i. Use the software to calculate the slope of the horizontal velocity-time graph
(both when the ball is on the tabletop and in the air).
Slope of Horizontal Velocity-Time Graph:
(on tabletop)
Slope of Horizontal Velocity-Time Graph:
(during the fall)
j. Print both graphs (on the same page if possible)
Question E: Describe the horizontal position vs. time graph. Be as specific as possible.
Question F: Describe the horizontal velocity vs. time graph. Be as specific as possible.
Final Questions:
1. What do you observe about the horizontal component graphs? Note differences
between when ball was on table and when ball was in the air. Be as specific as
possible.
2. Based on your velocity graph and measured slopes, does the horizontal motion of the
ball change substantially from during free fall compared to when it was on the table?
If so, how?
3. What is the significance of this observation?
4. How does the slope of the velocity vs time graph for free fall compare with the
rolling/projectile basketball (in the air)?
Phy 101: Fundamentals of Physics I
Instructor: Tony Zable, Ph.D.
5
5. Calculate the % error between the slope of the velocity vs time graph for free fall and
the rolling/projectile basketball (when it is in the air). Use the smallest value as the
“reference” value. Use the following equation:
%Error 
(Y _ Velocity  time _ slope ) free _ fall  (Y _ Velocity  time _ slope ) rolling_ ball
( Smaller _ of _ the _ Slope _ Values )
 100%
6. What is the significance of the slopes described in question 4?
7. How does the vertical motion of the rolling/projectile basketball (in the air) compare
with that of the dropped (free fall) basketball? What is the significance of this
observation?