Happy and Sad Balls: Observational Experiment

Aim

Observe the differences between the two balls and come up with an explanation for why the result of the interaction of the "happy' ball with the plank is different from interaction of the "sad" ball does not.

Prior Knowledge

• Impulse, momentum and kinetic energy, elastic and inelastic collisions, vector addition and subtraction.

Description of the Experiment

Observe the experiment. Record the outcome of the collision of the ball and the plank.

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Questions

1. What is the difference between the happy and sad balls when they collide with the table?
2. Which ball is heavier?
3. If you choose the table and the ball as a system for the moment of collision only, what happens to the momentum of the system?
4. What is the difference between the happy and sad balls when they collide with the plank? Shouldn't the sad ball that is heavier have a bigger impact on the plank?
5. Suggest possible explanations for this difference.
6. Repeat the analysis using the ball as the system only, and having the plank as an external object. What happens to the momentum of the system? Is the momentum constant? How do you know?
7. Is the momentum conserved in the collision if the ball is the system? What is the difference between the notions of constancy and conservation?