Changing Shape (Oxford AQA IGCSE Physics)

Changing Shape

• For stationary objects, multiple forces have to be applied to change their shape

• Objects can change their shape by:

  • compressing

  • stretching

  • bending

• A combination of all three shape changes can also occur

Compression

• An object is compressed when forces act:

  • in opposite directions

  • towards the object

• An example of compression is placing a mass on top of a spring placed on a flat surface

• The two forces are:

  • the weight of the mass on the spring

  • the normal contact force of the surface on the spring

Stretching

• An object is stretched when forces act:

  • in opposite directions

  • away from the object

• An example of stretching is placing a mass on the bottom of a spring hanging vertically from a rod

• The two forces are:

  • the weight of the mass on the spring

  • the normal contact force of the rod on the spring

• These two opposing forces cause a tension force in the spring

Compressing and stretching a spring

Bending

• An object is bent when multiple forces act:

  • in opposite directions

  • at different points on the object

• An example of bending is a diving board bending when a swimmer stands at the far end

• The two forces are:

  • the weight of the swimmer on the diving board

  • the normal contact force of the block on the dividing board

Forces on a diving board

Multiple forces acting on an object

Elastic distortions

• When some objects are stretched they will return to their original shape and length once the forces are removed

• Elastic distortion occurs when:

Objects return to their original shape when the stretching force is removed

• Examples of materials that undergo elastic distortion are:

  • rubber bands

  • fabrics

  • steel springs

Inelastic distortions

• Inelastic distortion occurs when:

Objects remain stretched and do not return completely to their original shape even when the stretching force is removed

• Examples of materials that undergo inelastic distortion are:

  • plastic

  • clay

  • glass

Elastic and inelastic distortions