24 Forces and Conservation Laws in Two Dimensions
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Date: _______________________
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Equipment
- Movie software file
- PuckCollision movie
- StandingJump movie
- LabPro interface
- Force Plate
- BigForce software file
- FrontalCrash movie
I. Two Dimensional Collision
Open Movie and select Insert/Movie. Find the movie PuckCollision and open it. Play the movie. The movie shows two pucks colliding on an air table. Return the movie to the first frame.
Scale the movie and extract position vs. time data for both pucks.
A. Momentum
To examine the collision in terms of momentum, rather than velocity, LoggerPro must be “taught” how to measure momentum.
To determine the x-momentum of puck1:
- Select Data/New Calculated Column and enter the appropriate name and units.
- In the equation box, enter the product of the mass of puck1 and its x-velocity. Use the Variables pull-down menu to select the appropriate variable for your equation. In this example, the equation should read: 0.050*”X Velocity”. (You can set both puck masses to 50 g since the error introduced by this simplification is much less than the error inherent in selecting pixel locations for the two pucks.)
Use this technique to create columns for:
- the x-momentum of each puck,
- the y-momentum of each puck,
- the total x-momentum in the system of the two pucks,
- and the total y-momentum in the system of the two pucks,
Create a graph of the x-momentum of each puck and the total x-momentum vs. time. Print, label, and attach this graph.
Extract data from this graph to complete the first row of the following table.
|
before collision |
after collision |
|
|
Total x-momentum |
± |
± |
|
Total y-momentum |
± |
± |
Create a graph of the y-momentum of each puck and the total y-momentum vs. time. Print, label, and attach this graph. Complete the above table.
Question: Which, if either, of the momentum defined above appear to be conserved in the collision? Which, if either, of the momentum should be conserved in a collision of this type? Explain.
B. Energy
Using Data/New Calculated Column create columns for:
- the kinetic energy of each puck,
- and the total kinetic energy in the system of the two pucks,
Create a graph of kinetic energy of each puck and the total kinetic energy vs. time. Print, label, and attach this graph.
Extract data to complete the following table.
|
before collision |
after collision |
|
|
Total kinetic energy |
± |
± |
Question: Does the kinetic energy defined above appear to be conserved in the collision? Should the kinetic energy be conserved in a collision of this type? Explain.
Question: Carefully watch the two pucks before and after the collision. Can you see where some of the initial kinetic energy in the system is “hiding” after the collision?
II. Vertical Leap
Open the movie StandingJump. Play the movie. The movie shows a man (5’8” tall and 160 lbs) performing a s