# Forces

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• Created by: mohap023
• Created on: 01-03-14 09:38

## Resultant Force

• When 2 objects interact, they always exert equal and opposite forces on eachother.
• Force is measured in Newtons using a Newtonmeter.

Context: when a car moves forward:

• the force of friction on the ground on the tyre is in the forward direction
• The force of friction on the ground is in the reverse direction

The resultant force is a single force that has the same effect as all the forces acting on the object.

When the resultant force on an object is zero, the object:

• remains stationary
• continues to move at the same speed and in the same direction as it was already moving
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For any car travelling at constant velocity the resultant force is on zero.

The braking force needed to stop a vehicle depends  on:

• the velocity of the vehicle when the brakes are first applied
• The mass of the vehicle
• The greater the velocity, the greater the deceleration needed to stop it in a certain distance.
• The greater the mass, the greater the braking force needed for a give deceleration.

Thinking distance = the distance travelled by a vehicle in the time it takes the driver to react

Braking Distance= the distance travelled by vehicle during the time the braking force acts

The stopping distance = thinking distance + braking distance

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## Stopping Distances

Factors Affecting Stopping Distances:

• tiredness, alcohol and drugs all increase reaction times and thinking distance
• The faster the vehicle is travelling, the further it travels before it stops
• In adverse road conditions (e.g-ice) drivers break with less force to avoid skidding. Stopping distances are therefore greater in poor road conditions.
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