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Impulse-Change in Momentum

Impulse-Change in Momentum. 3.1 Change in Momentum (2 days) Mr. Richter. Agenda. Warm-Up Intro to Change in Momentum Notes: Impulse-Change in Momentum Calculating Impulse Conservation of Momentum Objects Pushing Off of Each Other (Recoil) Problem Solving Practice

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Impulse-Change in Momentum

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  1. Impulse-Change in Momentum 3.1 Change in Momentum (2 days) Mr. Richter

  2. Agenda • Warm-Up • Intro to Change in Momentum • Notes: • Impulse-Change in Momentum • Calculating Impulse • Conservation of Momentum • Objects Pushing Off of Each Other (Recoil) • Problem Solving Practice • Momentum and Impulse Quiz Friday

  3. Objectives: We Will Be Able To… • Understand the relationship between the time interval for which a force is applied and the change in an object’s momentum. • Solve problems with changes in momentum. • Understand the relationship between Newton’s Third Law and the Law of Conservation of Momentum. • Calculate speeds of object’s pushing off of each other (recoil problems).

  4. Warm-Up: • If you were falling from a second floor window, would you be safer if you fell onto a concrete sidewalk or a mattress? Why? (Do not just say the mattress is softer.) • Discuss at your table, and we will discuss as a class in a few minutes.

  5. Impulse – The Change in Momentum

  6. Impulse – The Change in Momentum • To change the momentum of an object, assuming that it doesn’t lose any mass, you must change its speed. • It will either get faster or slower. • What is the difference between a car that gradually comes to a stop, and a car that slams into a wall? • Hint, the change in momentum is the same because the change in speed is the same.

  7. Impulse – The Change in Momentum • The difference between gradually coming to a stop and slamming into a wall is how long it takes. • Gradually coming to a stop: • it takes a long time • a small force is applied • Slamming into a wall • takes very little time • a large (dangerous) force is applied

  8. Impulse – The Change in Momentum • Impulse is the change in an object’s momentum. • Impulse depends on how much force is applied, and for how long. This determines by how much the speed of an object changes. Units: kgm/s (same as momentum)

  9. Practice Problems • A 1200-kg car traveling at 15 m/s comes to a stop. • What is its starting momentum? • What is its final momentum? • What is its change in momentum? • A 140-N force is applied to a 10-kg bowling ball for 3 seconds. What is the bowling ball’s change in momentum?

  10. Homework: • Impulse-Change in Momentum Worksheet • #1-4 Due Thursday • Separate Sheet of Paper!

  11. Warm Up: • What do we mean when we say that something is conserved? • Write 1-2 sentences in your notebook, then discuss at your table.

  12. The Law of Conservation of Momentum

  13. The Law of Conservation of Momentum • What does the word “conservation” mean? • You probably said “save” “don’t waste” maybe “preserve” • In physics, conservation means that nothing is lost or gained. Nothing is created or destroyed. • THE LAW OF CONSERVATION OF MOMENTUM: when we say that momentum is conserved, we mean:

  14. The Law of Conservation of Momentum • In other words: the total momentum that exists in a system does not change. Momentum just transfers from one object to another.

  15. The Law of Conservation of Momentum • Where does this law come from? • When two objects interact with each other: • they interact for the same amount of time • N3L says that the forces on the objects must be equal and opposite • If the forces are equal and opposite, then the momentums are equal and opposite! The man and the ball have equal momentum in opposite directions.

  16. Recoil

  17. Recoil • When two objects push off of each other from a stationary position, this is called recoil. • A skateboarder throwing a ball. • A person jumping off the Earth. • A rifle shooting a bullet. • Conservation of Momentum in Recoil: Momentum of Object 1 = Opposite of Momentum of Object 2

  18. Recoil Practice • An 80-kg astronaut floating (stationary) in space throws a 5-kg moon rock at 8 m/s forward. What is the astronaut’s speed after he throws the rock? • -0.5 m/s

  19. Wrap-Up: Did we meet our objectives? • Understand the relationship between the time interval for which a force is applied and the change in an object’s momentum. • Solve problems with changes in momentum. • Understand the relationship between Newton’s Third Law and the conservation of momentum. • Calculate speeds of object’s pushing off of each other (recoil problems).

  20. Homework • p. 81 -82 #6-9 • Study for your quiz!

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