P5- Action and Reaction

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  • Created by: Lauren
  • Created on: 10-03-13 14:55

Actions and Reactions.

Every action has an equal and opposite reaction. When an object collides with another or two bodies interact, they exert equal and opposite forces upon eachother; this is Newtons 3rd Law of Motion. 

For example, when you stand on solid ground: 

-you exert a force on the ground; your weight

-the ground exerts an equal and opposite force on you (contact force)

Gravity pulls you down towards the Earth and you are pulling the Earth towards you.


You can calculate momentum by using the following equation:

Momentum= Mass x Velocity 

An increase in the objects mass and/or velocity will also increase its momentum. 

Collisions, damage and injury

In a collision the velocities of the objects colliding are parallell. IF object A hits object B with a force, then object B hits object A with an equal force.

Acceleration is the rate of change of an objects velocity over time Many injuries in vehicle collisions, and sporting injuries, are caused by rapid acceleration(usually a sudden slowing down of the body). 

Safety features in vehicles reduce injury by spreading out the acceleration over a greater period of time. This means that the passengers momentum is reduced more slowly.

During a collision, two objects exert an equal and opposite force on eachother. You need to be able to calculate force, change in momentum and time taken using the following equation:

Force (N)= Change in momentum/time.

Spreading a change in momentum over a longer time reduces:

-the forces required to act

-injuries caused by the forces.

Conservation of Momentum

The total momentum of a system is the same after an event as it was before. 

Recoil- Total momentum of a gun…


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