Physics Demo Number: 001

Approximate Run Time: 5 min

3 to 1 Mass Ratio Energy and Momentum; and Spin Angular Momentum

Demo Description

Two demos are possible with this apparatus:

  1. Drop basketball with softball on top of it.

  2. Spin angular momentum (football)

 

Scientific Principles

  • Conservation of Momentum

  • Spin Angular Momentum

  • Conservation of Energy



Equipment

  • Football

  • Softball

  • Basketball

Equipment Location

  • Column [E-4-5] Kit (001) Parts One and Two

Instructions

Demo 1: Vertical 3:1 mass ratio (LEMON IMPACT APPARATUS) with a basketball and a softball.

Hold the  basketball at about waist level and place the softball on top of the basketball.

When released the two should fall to floor with the ensuing motion being the softball flying upwards with greatly enhanced speed and the basketball nearly dead still on the floor.

Suggested Explanation:

Gravity arranges the speeds of the two objects to be equal, just as they hit floor traveling together.

The floor then arranges for their velocities to be negatives of each other (assuming no interaction between the two during the (instantaneous) velocity-reversing interaction of the basketball with the floor)).

So now the two collide with equal and opposite velocities and hence, since 3 m=M, m moves off with all the energy and momentum.

Demo 2: Assume one possesses the ability to throw the football with spin about its long axis (and also without that spin).

Then if a suitable volunteer student assistant can catch the ball and return it, one should be able to show more precision in the ability to pinpoint a target with the stability lent to the trajectory of the ball when the ball has spin angular momentum.

Short of great athletic skills in throwing the football, it is probably best to just mention the concepts involved , while simply tossing the ball straight up with a spin along its long axis, and then with a tumbling motion about a horizontal direction.

Even if you are pro football quarterback material , the casual straight upward tosses and catches probably will make the point more convincingly to the students , since they don't have to make value judgments as to the validity of the results obtained in actual passes.

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Miscellaneous Parts List:

1. Tinker Toy Parts,   a Sand Pendulum, and An Inertial Balance are  in a  Kit on  [C--3-4].
 
Writeup created by David A. Burba
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