1 - FORCES AND MOTION 

The 3 laws of motion - 

1 - Balanced forces mean no change in velocity

• If the forces are balanced, on a non-moving object, it will just stay still 
• If the object is already moving, it will continue at the same velocity 

- a train going at a constant velocity has all the forces acting on it balanced - steady speed = no resultant force 

2 - A resultant force means acceleration 

• Unbalanced force = object accelerates in that direction 

- acceleration =starting, speeding up, stopping, slowing down, changing direction - on a force diagram the arrows will be unequal 
- the bigger the force, the greater the acceleration/deceleration 
- the bigger the mass, the smaller the acceleration 

Unbalanced force (resultant force) - 
Resultant force = mass x acceleration (F = ma)
Acceleration = resultant force/mass (a = F/m)


3 - Reaction forces 

•  If object A exerts a force on object B, object B exerts the exact opposite force on object 

- same sized forces in opposite directions 
- movement depends on mass etc. 
- eg: swimming