Topic 15: forces and matter

• Why does more than one force need to be applied when stretching, bending and compressing a spring

  • if one is applied the spring will move in the forces direction
  • Compression happens when both sides are forced inwards
• what are the two types of spring deformation

  elastic - where the object returns to its original shape

  plastic - the object doesn’t return to its original shape
• what is hookes law

  the extension of a spring is directly proportional to the force applied
• on a graph what is K (spring constant)

  gradient
• what is the elastic limit

  the point where the graph stops being linear and from then on does not obey hookes law
• what happens if the non linear line on a F/e graph is shallow

  • lots of extension for not much force
  • easy to stretch
• what happens if the line on a F/e graph is just linear

  • material is brittle
  • so snaps instead of stretching
• how is work done represented on a graph

  • area under the graph
• what is the equation for work done

  work done = 1/2 kx^2

  work done = 1/2 x spring constant x extension squared
• What is the difference between a linear and non linear relationship between force and extension?

  • linear - force and extension are directly proportional - straight line - obeying hookes law
  • Non linear - not directly proportional - curved line - not obeying hookes law
• what does the area under the force extension graph represent

  energy stored