Memory Anchor:

• Super Challenge:

  Stretch:

  Challenge:

Key Questions:

1. What forces are involved in stretching, bending or compressing an object?
   • Forces may change the shape of an object. An elastic object such as a spring stores elastic potential Energy when stretched or squashed. The extension of an elastic object is directly proportional to the Force applied.
2. Why, to change the shape of an object (by stretching, bending or compressing), does more than one force have to be applied?
   • If one Force only is applied to an object, for example a car, then the object will change speed or direction. If we want to change the shape of an object, we have to apply more than one Force to it.
3. What is the relationship between the work done on the spring and the elastic potential energy stores?
   • Provided the spring is not inelastically deformed, the work done on the spring and the elastic potential Energy stored are equal.
4. What is the difference between elastic deformation and inelastic deformation caused by stretching forces?
   • Elastic deformation is where a material changes in shape at low stress that is recoverable after the stress is removed. Inelastic deformation is caused a material is stretched beyond its limit of proportionality.
5. What is the relationship between extension and force for an elastic object, such as a spring?
   • The extension of an elastic object, such as a spring, is directly proportional to the Force applied, provided that the limit of proportionality is not exceeded.
6. What is the equation that links force, spring constant and extension? Include SI units.
   • (MS) Force = spring constant ? extension F = k e Force, F, in newtons, N spring constant, k, in newtons per metre, N/m extension, e, in metres, m This relationship also applies to the compression of an elastic object, where ?e? would be the compression of the object.
7. What is the difference between a linear and non-linear relationship between force and extension?
   • A linear relationship between Force and extension is a directly proportional one, where a non-linear relationship shows that an elastic object has exceeded its limit of proportionality.