# Forces and Motion

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• Created by: JJaquiery
• Created on: 12-02-20 06:49

## Momentum

Is a vector quanitity - has size and direction

p = mv (momentum = mass*velocity)

Conservation of momentum: in a closed system,the total momentum before and after a collision are equal

You can use the conservation of momentum to work out the velocity or mass of an object before or after a collision, as long as you have the relevant information about the collision

Note: velocity can be negative too, if it is the object is going in the opposite direction

Changes in momentum

When a resultant force acts upon an object, it causes its velocity, and so momentum, to change

force = change in mometum/change in time

There are many safety features of a car that mske the duration of the collision longer, so that the force acting on the person in the crash smaller, for example: crumple zones, seat belts and airbags

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## Inertia and Newton's Laws

Newton's First Law states: if the resultant force on a stationary objects is zero, the object will remain stationary. If the reultant force of a moving object is zero, the object will continue moving at a constant velocity.

A non-zero resultant force will always produce acceleration (or deceleration) in the direction of the force, the acceleration can take 5 different forms, starting, stopping, speeding up, slowing doen and changing directions. The lager the resultant force acting on an object, the more theobject accelerates, i.e. the force and acceleration are directly proportional.

Acceleration is also inversely proportional to the mass of the object

The formula that describes Newton's Secomd Law is: F = ma

Interia is the tendancy of motion to remain unchanged

An objects inertial mass measures how difficult it is to change an objects velocity, and inertial mass can be found usinf Newton's Second Law (m = F/a)

Newton's Third Law says that when two objects interact, the forces they exert on eah other are equal and opposite

An example of Newton's First Law in an equilibrium situation is a man pusing against a wall. As the man pushes the wall there is a normal cotact force pushing against him, these two forces are the same size.

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