1. IP2.1.5 What do forces do? © Oxford University Press 2011 What do forces do?

2. IP2.1.5 What do forces do? © Oxford University Press 2011  A resultant force changes the way something moves.  If an object is not moving (stationary), then a resultant force makes it begin to move, and if it is already moving a resultant force changes the way it moves.  A resultant force makes an object accelerate. It makes it speed up, slow down or change direction.

3. IP2.1.5 What do forces do? © Oxford University Press 2011 When this stationary snooker ball is struck by the moving cue ball it experiences a resultant force. What happens to the ball? It accelerates and moves in the direction of the resultant force.

4. IP2.1.5 What do forces do? © Oxford University Press 2011 This satellite in orbit around Earth experiences a resultant force due to gravity. It has a constant speed as it orbits and it does not crash down to the surface. What is the resultant force doing? It is making the satellite accelerate; in this case it is changing the direction of the satellite’s motion.

5. IP2.1.5 What do forces do? © Oxford University Press 2011  If there is NO resultant force acting on a body it does not accelerate.  This means it will continue travelling at the same speed in the same direction if it is moving or will remain stationary.  In deep space a moving object will continue moving at a constant speed in a straight line.

6. IP2.1.5 What do forces do? © Oxford University Press 2011 Zero resultant forceResultant force Stationary object Moving object Here is a summary of the effects of forces on objects. Remains stationaryStarts moving (accelerates) Continues moving at a steady speed in a straight line Accelerates in the direction of the resultant force (this might mean slowing down if the force is in the opposite direction to the motion of the object)