# Newtons Laws of motion and momentum

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Equation of momentum? scalar or vector?
Momentum (kg ms^-1) = mass (kg) x velocity (ms^-1). Vector
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Momentum is always conserved. How can you solve 2D collision problems?
Resolving vectors
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What's the difference between Elastic and Inelastic collisions?
In elastic collisions, momentum and kinetic energy are both conserved, whereas in inelastic collisions momentum is conserved but some kinetic energy is converted into other forms
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Give the two ways of stating impulse
average force x time. so impulse = change of momentum (Ns)
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State Newtons 1st Law
the velocity of an object will not change (remain at rest or moving in a straight line at a constant speed) unless a net force acts on it
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State Newtons 2nd Law
the rate of chnage of momentum of an object is directly proportional to the net force which acts on the object. F = change in p / change in t. F = ma
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Anddddd State Newtons 3rd Law
If an object A exerts a force on object B, then object B exerts an equal but opposite force on object A. (NOT if both forces act on the same object, e.g. book on table)
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Why are forces so high in a car crash?
F = change in p / change in t. Change in momentum is great and change in time in very little.
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What do crumple zones do?
absorb some of the car kinetic energy which would have been transferred to the passengers and increase time taken for the car to slow down - reducing force of passengers
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What other features increase the time in the collision?
Air bags and Seat belts (they stretch which also helps by absorbing some of the wearers kinetic energy)
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Risks to Seat belts and air bags?
Seat belts - bruising and dangerous for small children - may not secure them and cause injury to the neck. Air bags - dangerous without seat belts because they inflate rapidly with a lot of force, and rear-facing car seats
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## Other cards in this set

### Card 2

#### Front

Momentum is always conserved. How can you solve 2D collision problems?

#### Back

Resolving vectors

### Card 3

#### Front

What's the difference between Elastic and Inelastic collisions?

### Card 4

#### Front

Give the two ways of stating impulse

### Card 5

#### Front

State Newtons 1st Law