Physics GCSE, unit one forces and motion

Physics GCSE, unit one forces and motion 

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  • Created by: jesper
  • Created on: 17-03-12 06:15

Important terms, Unit 1

Type of forces - What is it?

Push- A force.
Friction- A force that opposes motion.
Normal reaction force - The force that acts in an upwards direction.
Gravitational force/weight- The pull of the earth.
Air resistance- A force taht opposes the movement of objects in air.  
Upthrust- An upward push.
Magnetic force- used to make electric motors rotate.
Electrostatic force- To do wit the attractions and repulsions between charges.

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Vector and Scalar

Vector changes in size and direction. 

For example:

  • Velocity.
  • Force.
  • Acceleration.
  • Momentum.

Scalar only changes in size.

For example:

  • Temperature
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Newtons's law of motion

Newton's 1st law
If the forces on an object is balanced – there is no resultant force – the object will either remain at rest or carry on moving at constant speed in a straight line. If the forces on an object is unbalanced, the object will accelerate.

Newton's 2nd law 
Resultant force (N) = mass (kg) x acceleration (m/s
2) or F = ma

Newton's 2nd law 
For every action there is an equal and opposite reaction.

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Terminal velocity

Terminal velocity is when the upward force is the same as the downward force.


 When a skydiver jumps off the plane, she will accelerate until she reaches terminal velocity. When her parachute opens, it will cause a sudden increase in drag force. This means that there will be an unbalanced force acting upwards, causing her to decelerate. As she slows down, the drag force decreases and a new terminal velocity is reached.

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Thinking distance and Braking distance

Thinking distance= is the time takn for the driver to respond or react
This could be increased if the driver is tired, under the influence of alcohol or drugs/ or poor visability. 

Braking distance= is the time takenfor the vehicle to rest after the driver hits the brakes. This could be increased if the road is slipperry or the tyres are screwed up.

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The Turning effect of forces

Moment(Nm)= Force(N) x Perpendicular distance from the pivot(m)

An object will be balanced if:
Sum of anticlockwise moments = sum of clockwise movements 

Hooke's law:

load force is directly proportional to extension provided that it is within its elastic limit


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