大象传媒

Deformation

When a acts on an object, the object may change shape by bending, stretching or compressing - or a combination of all three shape changes. However, to change the shape of a stationary object there must be more than one force acting to do the following.

Bend an object's ends, eg diver about to jump off a diving board.

A beam is bent.Two equal forces act inwards to support left hand end. A third force bends the right had end downwards.

Pull an object's ends apart, eg when a rubber band is stretched.

A beam is聽stretched by two equal forces. Beam聽is thinner in the middle to indicate stretching. Arrows聽at聽each end indicate direction of force.

Push an object's ends together, eg when an empty drinks can is squashed.

A beam聽is squashed by two equal forces. Beam聽is thicker in the middle to indicate compression. Arrows either end point inwards to indicate direction of force.

A change in shape is called :

  • deformation is reversed when the force is removed
  • deformation is not fully reversed when the force is removed - there is a permanent change in shape

A rubber band undergoes elastic deformation when stretched a little. A metal drinks can undergoes inelastic deformation when it is squashed.

When a material is stretched or compressed the separation between the particles is changed. In elastic deformation, the spacing will return to its original state once the force is removed. In inelastic deformation, the spacing between particles will remain changed once the force is removed.