Hooke's Law (Edexcel IGCSE Physics)

• The relationship between the extension of an elastic object and the applied force is defined by Hooke's Law
• Hooke's Law states that:

The extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

• Directly proportional means that as more force is applied, the greater the extension (and vice versa)
• The limit of proportionality is where if more force is added, the object may extend but will not return to its original shape when the force is removed (it will be inelastically deformed)
  • This limit varies according to the material

Hooke's Law states that a force applied to a spring will cause it to extend by an amount proportional to the force

The Force-Extension Graph

• Hooke’s law is the linear relationship between force and extension
  • This is represented by a straight line on a force-extension graph

• Any material beyond its limit of proportionality will have a non-linear relationship between force and extension

Hooke's Law is associated with the linear region of a force-extension graph

• 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 deformed (stretched)

• 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