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 the force is increased, the extension increases 
  • If the force is doubled, then the extension will double
  • If the force is halved, then the extension will also halve
• The limit of proportionality is the point beyond which the relationship between force and extension is no longer directly proportional 
  • 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. Beyond the limit of proportionality, Hooke's law no longer applies

• Elastic behaviour is the ability of a material to recover its original shape after the forces causing the deformation have been removed
• Deformation is a change in the original shape of an object
• Deformation can be either: 
  • elastic
  • inelastic

Elastic Deformation

• Elastic deformation is when the object does return to its original shape after the deforming forces are removed
• Elastic deformation results in a change in the object's shape that is not permanent

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

Inelastic Deformation

• Inelastic deformation is when the object does not return to its original shape after the deforming forces are removed
• Inelastic deformation results in a change in the object's shape that is permanent

• Examples of materials that undergo inelastic deformation are:
  • Plastic
  • Clay
  • Glass

Elastic behaviour of a spring

The spring on the right has undergone inelastic deformation, it's shape has been permanently deformed