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Chapter 6 - Momentum and Collisions

Chapter 6 - Momentum and Collisions. 6.1 - Momentum and Impulse. Review. Energy cannot be created or destroyed, but only changed from one form to another Newton’s 3 laws Kinetic energy is the energy of motion: KE=1/2 mv 2. Momentum and Impulse.

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Chapter 6 - Momentum and Collisions

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  1. Chapter 6 - Momentum and Collisions 6.1 - Momentum and Impulse

  2. Review • Energy cannot be created or destroyed, but only changed from one form to another • Newton’s 3 laws • Kinetic energy is the energy of motion: KE=1/2 mv2

  3. Momentum and Impulse • Momentum is a vector quantity defined as the product of an object’s mass and velocity • SI units are kilogram-meters per second

  4. Momentum and Impulse • A change in momentum takes force and time • Impulse-Momentum Theorem or

  5. Momentum and Impulse • Explains why follow-through is important in many sports • Impulse is the product of the force and the time over which it acts on an object • Determines stopping times and distances

  6. Momentum and Impulse • A change in momentum over a longer time requires less force • Example • The egg fall

  7. HW Assignment • Page 209: Practice 6A • Page 211: Practice 6B • Page 213: Practice 6C

  8. Chapter 6 - Momentum and Collisions 6.2 - Conservation of momentum

  9. Conservation of momentum • We have looked at the momentum of one object • If two or more objects are interacting with each other then the total momentum of all objects remains constant regardless of the nature of the forces between the objects

  10. Conservation of momentum • Momentum is conserved in collisions • Momentum is also conserved for objects pushing away from each other total initial momentum = total final momentum

  11. Chapter 6 - Momentum and Impulse 6.3 - Elastic and inelastic collisions

  12. Perfectly inelastic collisions • A collision in which two objects stick together and move with a common velocity after colliding • After the collision, the two objects become essentially one object

  13. Perfectly Inelastic Collisions • In this case, we get a simplified version of the equation for conservation of momentum • using this equation, pay attention to the signs indicating direction • What happens in terms of Kinetic Energy?

  14. Perfectly Inelastic Collisions • Consider the following Situation: • m1 = 1kg v1 = 5 m/s • m2 = 2kg v2 = 3 m/s

  15. Conservation of Momentum • Video Demonstration

  16. Practice Problem • A clay ball with a mass of 0.35 kg hits another 0.35 kg ball at rest, and the two stick together. The first ball has an initial speed of 4.2 m/s. • What is the final speed of the balls? • Calculate the decrease in kinetic energy that occurs during the collision • What percentage of the kinetic energy is converted to other forms of energy?

  17. Elastic Collision • When two objects collide and return to their original shapes with no change in momentum and no change in total kinetic energy

  18. Collisions • Most collisions are neither elastic nor perfectly inelastic • Even in nearly elastic collisions, there is some deformation and loss of kinetic energy as a result • In most collisions, some kinetic energy is converted into sound

  19. HW Assignment • Page 224, Practice 6E: 1, 3, 5 • Page 226, Practice 6F • Page 229, Practice 6G: 1, 3, 4

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