Physicists Can’t Jump
Instructor Notes
Set-up Notes
Force plate should be placed on a hard surface. If the floor is carpeted, place force
plate on a few whiteboards to reduce the dampening effect of carpet.
Note: Students must keep arms in a consistent orientation to keep their center of
mass constant. Try having them keep their arms at their sides.
Data Collection Notes:
LoggerPro: The CantJump.cmbl file has settings as indicated below.
• Sampling rate 500 samples/second.
• Optional: Trigger function may be turned on Trigger in Data Collection.
• Zero force scale in LoggerPro with student on it prior to activity.
Video capture:
Remember to include a scale in the plane of motion.
After capturing video, insert into LoggerPro (.avi, .mov, or any movie that can be
played by QuickTime).
Force Table Analysis
Graphically determine impulse on the Force vs. Time graph in LoggerPro.
Select the area of the jump (as shown below) and use the Integration tool.
Video Analysis
Set scale and origin. Determine the jump height from the y data by adding a point at
the bottom and top of the jump.
ATE Workshop for Physics Faculty, 2013
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Soft Landing
For the first trial, you will use the same data collection process (force plate data)
and mathematical analysis as with “Jumping Off”.
• Use jump height (10 cm) & kinematics to calculate velocity: v2 = v o 2 + 2a Δ y
• Then use the mass and impulse equation to calculate impulse: I = m Δv
Results
a. Softer landing (bent knee)
Impulse should be lower due to the increased time of collision.
b. Harder landing (straight knee)
Impulse should be higher.
Sample data:
m = 92.25 kg
h = 0.10 m
bent knee: I = 138 Ns
straight knee: I = 120.6 Ns
Hang Time
Note: Students should keep arms at their side to maintain a constant center of mass.
Students will naturally move their arms in an effort to jump higher or increase their
hang time.
Sample data:
m = 92.25 kg
Readings from LoggerPro
Before I = 322.8 Ns
After I = 299.5 Ns
hang time from logger pro t = 0.60 s
Use Impulse equation to calculate velocity before and after: I = m Δv
Use velocity & kinematics to determine time: v2 = v o 2 + 2a Δ y
Calculate hang time using kinematics: v = v o + at
Calculate height using time and kinematics: Δ y = v o t + ½ at2
Calculated:
Before v = 3.49 m/s
Δ y= 0.624 m
t = 0.356 s
Hang time = 0.71 s
(double calculated time to account for total hang time)
ATE Workshop for Physics Faculty, 2013
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