Forces and Elasticity

• Forces don't just make objects move they can also make them change shape. Whether they change shape temporarily or permanently depends on the object and the forces applied.
• Stretching, Compressing or Bending

  1. Apply a force to an object

  2. Requires more than one force acting on the object

  3. Work is done when a force stretches or compresses an object and causes energy to be transferred to the elastic potential energy store of the object

  4. If it is elastically deformed, all this energy is transferred to the object's elastic potential energy store
• Elastic deformation


  An object has been elastically deformed if it can go back to its original shape and length after the force has been removed
• Elastic objects


  Objects that can be elastically deformed (e.g. a spring)
• Inelastic deformation


  An object has been inelastically deformed if it doesn't return to its original shape and length after the force has been removed
• Extension is directly proportional to force


  The extension of a stretched spring (or certain other elastic objects) is directly proportional to the load or force applied
• Spring constant, k


  • Depends on the material that you are stretching - a stiffer spring has a greater spring constant
• The equation also works for compression (where e is just the difference between the natural and compressed lengths -the compression)
• Limit of proportionality


  The maximum force above which the graph curves, showing that extension is no longer proportional to force
• Force increases


  Extension is no longer proportional to force
• You might see graphs with these axes the other way around-extension-force graphs. The graph still starts with a straight part, but starts to curve upwards once you go past the limit of proportionality, instead of downwards.