Phys205A_Lecture23

Physics for Scientists & Engineers with Modern Physics (4th Edition)

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Chapter 9 Collisions
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Collisions – Characteristics z We use the term collision to represent an event during which two particles come close to each other and interact by means of forces z May involve physical contact, but must be generalized to include cases with interaction without physical contact z The time interval during which the velocity changes from its initial to final values is assumed to be short z The interaction forces are assumed to be much greater than any external forces present z This means the impulse approximation can be used
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Collisions – Example 1 z Collisions may be the result of direct contact z The impulsive forces may vary in time in complicated ways z This force is internal to the system z Observe the variations in the active figure z Momentum is conserved
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Collisions – Example 2 z The collision need not include physical contact between the objects z There are still forces between the particles z This type of collision can be analyzed in the same way as those that include physical contact
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Types of Collisions z In an elastic collision, momentum and kinetic energy are conserved z Perfectly elastic collisions occur on a microscopic level z In macroscopic collisions, only approximately elastic collisions actually occur z Generally some energy is lost to deformation, sound, etc. z In an inelastic collision, kinetic energy is not conserved, although momentum is still conserved z If the objects stick together after the collision, it is a perfectly inelastic collision
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Collisions, cont z In an inelastic collision, some kinetic energy is lost, but the objects do not stick together z Elastic and perfectly inelastic collisions are limiting cases, most actual collisions fall in between these two types z Momentum is conserved in all collisions
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Phys205A_Lecture23 - Chapter 9 Collisions Collisions...

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