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Newton’s Third Law of Motion

Newton’s Third Law of Motion. Momentum and The Conservation of Momentum. Newton’s Third law Momentum. For every action there is an equal and opposite reaction. Forces always come in pairs: Action force Reaction force. Action/reaction pairs. Identifying Action and Reaction Pairs

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Newton’s Third Law of Motion

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  1. Newton’s Third Law of Motion Momentum and The Conservation of Momentum

  2. Newton’s Third lawMomentum • For every action there is an equal and opposite reaction. • Forces always come in pairs: • Action force • Reaction force

  3. Action/reaction pairs • Identifying Action and Reaction Pairs • Both are always there when a force appears • They always have the exact same strength • They always act in opposite directions • They always act on different objects • Both are real forces and either can cause acceleration

  4. Momentum • What is momentum? • What does it mean if an object has momentum? Try to use force, speed, and acceleration in your description.

  5. Momentum • If two kids on skateboards are moving toward you and each one has a mass of 40 kg. One is moving at 10 m/sec and the other is moving at 20 m/sec, which one is harder to stop? Why?

  6. Momentum • Momentum is the mass of an object multiplied by its velocity. • This explains why faster moving objects are harder to stop. • It also explains/illustrates why objects with more mass are harder to stop.

  7. Explain how inertia is related to Newton’s Third Law and Momentum. Use complete sentences!

  8. Momentum; formula and units • Note the units for momentum are kg m/sec which is quite different that what we are used to!!

  9. Impulse

  10. Impulse • Momentum of an object can change That happens when the velocity of the object changes • Since force is what changes an object’s velocity, that means that force is ALSO responsible for changing momentum. • A change in momentum is created by a force exerted over time which is called an impulse

  11. Momentum and Impulse • Note that the momentum before she hits the ball is -3 kg m/sec • The impulse is the force applied for .1 sec • The new momentum is 3 kg m/sec because • The change in momentum is 6 N sec • The change in momentum MUST equal the impulse

  12. If a 500 kg car is traveling at 45 m/sec, what is the momentum of the car? • If a 15 N force is applied to a baseball for .3 seconds, what is the impulse applied to that ball?

  13. Impulse • Impulse is = Force x time • Impulse = Ft Units are Newton seconds

  14. Change in Momentum Change in Momentum = Final Momentum – Initial Momentum or -

  15. Impulse is equal to change in momentum

  16. How do you find the change in momentum of an object? Explain in your own words. • If an impulse of 2 N sec is applied to an object, what is its change in momentum?

  17. Solve these Problems • You throw a basketball in one direction with 20 Newtons of force. Newton’s Third Law states that there is an equal and opposite force. If there are two equal forces applied, how is it that the ball “accelerates”? • If a hockey player has a mass of 60 kg and is moving with a velocity of 3 m/sec, what is his momentum? • If the same hockey player experiences an impulse of 2 N sec, what will his “change in momentum” be?

  18. Problems continued • If there is a hockey player with a mass of 60 kg and he experiences a force of 2 N for .2 seconds, what will his change in momentum be? • Using the information from above, what is the initial velocity of the player if his final velocity is 5 m/sec?

  19. Problems continued • If a 15 N force is applied, for 10 seconds, to a 1 kg ball that is initially at rest, what is the ball’s final momentum? (hint, you need to consider the ball’s change in momentum and impulse) 2. How much time should a 100 N force be applied to increase a 10 kg car’s velocity from 10 m/sec to 100 m/sec?

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