Chapter 6 - Momentum and Collisions

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Chapter 6 - Momentum and Collisions

• 6.1 - Momentum and Impulse

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Review

• Energy cannot be created or destroyed, but only
  changed from one form to another
• Newtons 3 laws
• Kinetic energy is the energy of motion KE1/2
  mv2

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Momentum and Impulse

• Momentum is a vector quantity defined as the
  product of an objects mass and velocity
• SI units are kilogram-meters per second

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Momentum and Impulse

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

or
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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

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Momentum and Impulse

• A change in momentum over a longer time requires
  less force
• Example
• The egg fall

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HW Assignment

• Page 209 Practice 6A
• Page 211 Practice 6B
• Page 213 Practice 6C

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Chapter 6 - Momentum and Collisions

• 6.2 - Conservation of momentum

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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

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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
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Chapter 6 - Momentum and Impulse

• 6.3 - Elastic and inelastic collisions

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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

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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?

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Perfectly Inelastic Collisions

• Consider the following Situation
• m1 1kg v1 5 m/s
• m2 2kg v2 3 m/s

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Conservation of Momentum

• Video Demonstration

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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?

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Elastic Collision

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

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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

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HW Assignment

• Page 224, Practice 6E 1, 3, 5
• Page 226, Practice 6F
• Page 229, Practice 6G 1, 3, 4