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24. Momentum (Paul, a former boxer, investigates the physics of riding with a punch, and other situations related to momentum.) End Question: When you are lucky enough to catch a fly ball with your bare hand while watching a baseball game, your hand will be best off if you catch the ball with your hand extended toward the ball, then while contact is being made, pulling your hand back, gradually stopping the ball. In terms of impulse-momentum, explain why this is so. |
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25. Conservation
of Momentum (Paul shows how Newton’s laws lead to the impulse-momentum relationship, which then leads to the conservation of momentum.) End Question: Suppose a freight-train car rolls along a track at 10 m/s and collides with an identical freight car at rest. The two cars couple together and move as one along the track. How fast do the coupled-cars move? |
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26. Fish-Lunch
Momentum Problem (Paul illustrates momentum conservation with a two-fish system.) End Question: How fast would the small fish have to swim before lunch to halt the large fish in its tracks? |
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27. Freddy-Frog
Momentum Problem (Paul explains two ways that Freddy the Frog slows a horizontally-moving skateboard by vertically falling on it.) End Question: Suppose the situation is the same, but Freddy’s mass is 2 kg. What is the speed of the skateboard when Freddy lands on it and takes a ride? |