notes: chapter 11.3 newton’s third law of motion and momentum
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Notes: Chapter 11.3 Newton’s Third Law of Motion and Momentum
Newton’s Third Law of Motion
• For every action force there is an equal and opposite reaction force.
• Called force pairs or action/reaction pairs
• Force pairs do not act on the same object, and thus don’t always have the same effect!
• Movie: Newton's third
Newton’s Third Law of Motion
• The equal forces don’t always have the same effect, though.
• According to the second law, F=ma. You will have different results depending on their masses.
Momentum• An extension of Newton’s Third
Law…tells what will happen from the action/reaction
• Is equal to mass x velocity• p = mv• units have no name, just kg . m/s
Momentum & Collisions
• In collisions, momentum is conserved for the system (both balls), that is, it is the same for all the objects before and after the collision.
• Called The Law of Conservation of Momentum
Law of Conservation of Momentum
• The system is both of the pool
balls. If they have the same mass:– the total momentum
before is mv + m0 = mv
– the total momentum after is m0 +
mv = mv
Law of Conservation of Momentum
• What if the red ball has twice the mass of the
white one? How fast will it move?
• What if the white ball has twice the mass of the red one? How fast will it move?
Momentum & Collisions
• Elastic collision: objects hit each other and don’t stick together (bounce off)
• Inelastic collision: objects hit each other and stick together
• Momentum and Collisions• Conservation of Momentum
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