# 5.3.1 Changing Shape

### Forces & Changing Shape

• For stationary objects, more than one force has to be applied to change their shape
• Their shape can change by:
• Stretching (forces in opposite directions away from the object)
• Bending (forces that distort the object)
• Compressing (forces in opposite directions towards the object)
• A combination of all three shape changes can also occur

#### Compression

• 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
• The reaction force from the surface to the spring
• These two forces are towards each other

The compression or stretching of a spring requires two forces

#### Stretching

• An example of stretching is placing a mass on the bottom of a vertically hanging spring
• The two forces are:
• The weight of the mass
• The tension in the spring
• These two forces are away from each other
• These opposite forces are a result of Newton's Third Law

#### Bending

• 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
• The reaction force from the block to the dividing board
• These two forces act towards each other, but at different points on the object
• Bending can also be caused by two forces at an angle to each other

Forces on a diving board cause it to be bend when a swimmer stands on one end

More than one force on an object can cause it to bend

### Elastic & Inelastic Deformation

• When some objects, such as springs or rubber bands, are stretched they will return to their original shape and length once the forces are removed
• Other materials, such as plastic, remain permanently distorted (stretched)

Elastic materials return to their original shape and size after stretching whilst plastic materials don’t

• A change of shape is called a deformation and can either be:
• Elastic
• Inelastic

#### Elastic Deformation

• Elastic deformation occurs:

When objects return to their original shape when the stretching force is removed

• Examples of materials that undergo elastic deformation are:
• Rubber bands
• Fabrics
• Steel springs

#### Inelastic Deformation

• Inelastic deformation 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 deformation are:
• Plastic
• Clay
• Glass

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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