Forces and elasticity

• Forces are responsible for changing the motion of objects.
• If more than one force is present, the shape of an object can also be changed.
• The unit of force is the newton (N).
• When a force acts on an object, the object may change shape by bending, stretching or compressing - or a combination of all three shape changes.
• Pull an object's ends apart, eg when a rubber band is stretched.
• Push an object's ends together, eg when an empty drinks can is squashed.
• A change in shape is called deformation.
• Elastic materials return to their original shape and size after being stretched or squashed.
• Inelastic materials do not return to their original shape and size after being stretched or squashed.
• A rubber band undergoes elastic deformation when stretched a little.
• A metal drinks can undergoes inelastic deformation when it is squashed.