Download Forces and Energy Summary Sheet File

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Know that forces are measured in units called the Newton (N)
Know that mass is a measured of how much matter is in an object and is measured in
kilograms (kg).
Know that weight is the force of gravity acting on an object and is measured in
Newtons (N).
The formula linking mass and weight is:
Weight = Mass x Gravity
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A Resultant force can be found by adding or subtracting forces.
If the resultant force is zero then an object will be stationary or moving with a constant
speed.
The resultant force causes the change in motion.
The amount of acceleration can be calculated using the following formula:
Resultant force = Mass x acceleration
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To every force there is an equal and opposite force.
These paired forces are called action and reaction forces.
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When an object moves through the air the air causes both a resistance and a friction
force.
When the driving force and the air resistive forces become balanced there is no
resultant force and the object moves with a terminal velocity.
Objects falling through the air fall due the force of gravity.
The acceleration of free-fall is approximately 10 m/s2.
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When a force acts on an object is transfers energy to the object.
Energy is measured in joules (J).
The amount of energy transferred is called the work done by the forces.
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The formula for work done is:
Work done = Forces x Distance
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Gravitational Potential Energy is the energy an object has due to its height above the
ground.
The formula for the change in GPE is:
Change in GPE = Mass x gravity x change in height
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Kinetic Energy is the energy an object has due to its motion.
The formula for KE is:
KE = ½ mass x (speed)2
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The overall stopping distance for a car is made up of two sections:
1. Thinking distance – this is the distance travelled by a car when the driver is
reacting.
2. Braking distance – this is the distance travelled by a car when the driver has his
foot on the brake.
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Thinking distance is affected by factors which influence the driver’s reaction time e.g.
alchol + drugs, tiredness, age.
Braking distance is affected by things which influence the forces of friction e.g.
condition of the brakes, wetness of the road surface.
Road safety has been improved by the introduction of speed limits and road side speed
cameras in order to slow down traffic.
Passenger safety has been improved by car technology such as air bags and crumple
zones.