# Shared Flashcard Set

## Details

Lecture 4
19
Physics
06/17/2011

Term
 What is momentum
Definition
 is measure of an objects tendancy to continue on it's present path
Term
 how can the momentum of an object increase
Definition
 increase the velocity, or increase the mass
Term
 what is the equation for momentum and what are it's units
Definition
 p=mv   momentum's units are: kg m/s
Term
 in an isolated system, what is the number one inviolable rule of momentum
Definition
 that momentum is always conserved
Term
 momentum is also a vector, what does this mean in terms of initial momentum and final momentum
Definition
 the initial momentum of the center of mass is equal to the final momentum in both direction and magnitude
Term
 Describe what an elastic collision is
Definition
 When two bodies come into contact with one another, the force generated by the deformed bodies is proportional tothe degree of the deformity.  If Hooke's Law is followed, the energy is conserved, and all the energy is transferred back into the motion of the bodies
Term
 Why are elastic equations easy
Definition
 Because the sum of the initial mechanical energies is equal to the final sum of mechanical energies
Term
 what are inelastic collisions
Definition
 These are collisions in which some of the mechanical energy is lost to internal energy
Term
 If any mechanical energy is lost, what type of collision is this
Definition
 This is an inelastic collision
Term
 What is a completely inelastic collision
Definition
 When two objects stick to each other
Term
 What is a reverse collision
Definition
 In a completely inelastic collison, two bodies will stick together and their final momentum equals zero.  Therefore, the initial momentum equals zero.  To understand a reverse collision mechanism, think of these objects as intially being stuck together and then exploding.  The initial momentum is zero, so therefore the final momentum is zero.
Term
 What is the equation for a reverse equation, and give an exmaple of it.
Definition
 A cat is standing on a frictionless board on a frictionless frozen lake, when it jumps to the right, the board must be pushed to the left to conserve energy.     M1V1=M2V2
Term
 When does a partially inelastic collision occur
Definition
 When a object moving at velocity strikes another object that is stationary but of equal mass to the first object.
Term
 The context is: this is a partially inelastic mechanism.  Describe how to find the final velocity of the stationary object and the moving object
Definition
 The stationary object will be less than the initial velocity of the moving object, but greater than the initial velocity divided by 2.   The moving object will be greater than zero, but less than  the initial velocity divided by 2.
Term
 In a partially inelastic mechanism, is it possible that a moving object could strike a stationary object and bounce backwards
Definition
 Yes.  If the stationary object has a large enough mass, it could potentially send that moving object backwards after the collision.
Term
 what is impulse and give its equation
Definition
 The change in momentum, J= delta P
Term
 Context: If a collision approximately follows Hooke's Law, the force during the time of collision is not constant.  How can we find the average force from that change in momentum
Definition
 delta MV= F avg * delta t
Term
 Explain how air bags work
Definition
 If the change in time is increased, we know that the average F exerted on a person is decreased.  therefore, air bags simply increase the amount of time it takes for the change in momentum to occur, thus lowering the overall force exerted
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