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6.2 Conservation of Momentum

6.2 Conservation of Momentum. pp. 215 - 221 Mr. Richter. Agenda. Warm-Up Check HW Return Lab Notebooks Intro to Conservation of Momentum Notes: N3L and Conservation of Momentum Conservation of Momentum Recoil Lab Wednesday. Objectives: We Will Be Able To….

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6.2 Conservation of Momentum

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  1. 6.2 Conservation of Momentum pp. 215 - 221 Mr. Richter

  2. Agenda • Warm-Up • Check HW • Return Lab Notebooks • Intro to Conservation of Momentum • Notes: • N3L and Conservation of Momentum • Conservation of Momentum • Recoil • Lab Wednesday

  3. Objectives: We Will Be Able To… • Describe the interaction between two objects in terms of the change in momentum of each object. • Compare the total momentum of two objects before and after they interact. • State the law of conservation of momentum. • Predict the final velocities of objects after collisions, given the initial velocities.

  4. Warm-Up: • A man and an elephant standing on skateboards push off of each other. • Which, if either, pushes with more force? • Which, if either, pushes for a longer amount of time?

  5. Newton’s Third Law and Conservation of Momentum

  6. N3L and Conservation of Momentum • When two objects collide they push off of each other. • According to Newton’s Third Law, they push with equal and opposite forces. • Also, they must push for the same amount of time. One cannot push the other without being pushed as well. • This means that their impulses (FΔt) are equal and opposite, which means their change in momentum must be equal and opposite as well.

  7. N3L and Conservation of Momentum • Algebraically:

  8. The Law of Conservation of Momentum • In words: the total momentum of all objects interacting with one another remains constant, regardless of the nature of the forces between the objects. • Momentum is conserved whenever two or more objects collide (more on specific types of collisions in the next section) • This is only true in the absence of friction.

  9. Momentum Conservation Example Before the Collision After the Collision

  10. Conservation of Momentum: Problem Solving • A 20 kg Object A traveling to the right at 5.0 m/s collides with a stationary 15 kg Object B initially at rest. After the collision, object A continues moving to the right at 4.0 m/s. What is Object B’s velocity after the collision? • 1.3 m/s to the right

  11. Recoil When objects push off of each other.

  12. Recoil • Recoil scenarios are special types of collisions when two objects push off of each other when both are initially at rest. • Some examples (all are assumed frictionless): • Our warm up, with the man and the elephant. • Shooting a rifle • Two ice skaters pushing away

  13. Recoil • The conservation of momentum equation changes when both initial velocities are zero. • The momentum of one object is equal and opposite the momentum of the other object in recoil scenarios.

  14. Recoil Problem Solving • An 80.0 kg man and a 400 kg elephant stand next to each other on skateboards. If they pushed off of each other, the man would move to the left at 12.0 m/s. What would the elephant’s velocity be? • 2.40 m/s to the right

  15. Wrap-Up: Did we meet our objectives? • Describe the interaction between two objects in terms of the change in momentum of each object. • Compare the total momentum of two objects before and after they interact. • State the law of conservation of momentum. • Predict the final velocities of objects after collisions, given the initial velocities.

  16. Homework • Due Thursday • p. 219 #1, 2, and 4 • p. 221 #1-3

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