# Forces, Motions and Energy

• Created by: Saira147
• Created on: 20-04-15 09:33

## Resultant Force

When the resultant force has equal amount of force on both sides of an object the object is stationary.

If there is a bigger force on one side you can find the newton by subtracting one side from the other force you are trying to find. So if there was 10N force on the left side and 20N force on the right then the overall force would be 10N to the right.

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## Moving object-resultant force

If an object is moving, a car for example there is air resistance and friction pulling the car back and the acceleration force infront.Work out the resultant force in the same way. For a MOVING object

If the Resultant force = 0 than the car is a steady speed.

If the resultant for is NOT 0 than the object accelerates in the given direction.

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## velocity and acceleration

velocity- how far something is moving in a certain direction

speed= distance/time

acceleration= final velocity - initail velocity/ time (a= u-v/t)

acceleration unit is m/s2 (metres per second squared)

negative acceleration is the same as slowing down. aka deceleration

velocity time graph - distance = area under the graph

a = f/m acceleration= force (resultant)/ mass

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## Terminal Velocity

Terminal velocity is to do with objects falling through fluids. (liquid or gas)

1. weight pulling down and air resistance in the opposite direciton, so the acceleration is downwards.

2. accelerating less

3. forces become balance so the object is falling at a steady speed this is know as terminal velocity.

4. when a parachute opens the upward force increaser causing the object to slow down

5. force balance out again, slower terminal velocity.

also should know how to interpret this on a graph

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## Forces and Elasticity

Streching the spring means work has been done. Work means that energy has been transferred, giving the spring elastic potential energy.

Hooke's Law-

The extention of an elastic object is directionally proportional to the force applied, given that the limit of proprtionality is not exceeded. (over streched)

mass and force are not the same

f = k x e   force = spring constant x extention

work is measured in joules

work= force x distance

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## Power and Work

power = work done / time taken

power is measures in watts

kinetic and gravational potentioal is a type of energy. Kinetic is movement. Gravitational potentional the amont something is about the ground.

kinetic energy = 1/2 x mass x velocity2 squared.

change in gravitational potentional energy= mass x gravitational field strength x height

gravitational field strength of earth is 10N/kg

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## weight

Wieght is a force measured in Newtons, weight is measured downwards towards the centre of the earch.

Mass is measures in kg, weight in Newtons

Weight = mass x gravitational field strength      (w =m x g)

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