forces and elasticity

• Why are elastic materials different to inelastic materials?

  inelastic materials do not return to their original length when the forces are remove, whereas elastic materials do return to their original length and shape
• Give 6 examples of elastic materials

  
  

  - slinky

  - rubber bands

  - rubber gloves

  - eraser

  - playground surface

  - tennis ball
• How is work done in relation to forces and elasticity?

  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

  
  

  If it is elastically deformed

  All this energy is transferred to the elastic potential energy store
• What is elastic deformation?


  - a temporary change in shape

  that is self-reversing after the force is removed, so that the object returns to its original shape

  
  

  - e.g. stretching, compressing, bending
• What is inelastic deformation?

  - inelastic deformation occurs when an object is stretched beyond its elastic limit

  - when the applied force is removed the object does not return to its original size/shape
• What is the equation for the force needed to stretch an elastic object?


  
  

  Force = spring constant x extension

  F (N) = k (N/m) x e (m)

  F = ke

  
• What can 'e' in the equation 'F = ke' also represent?

  - compression instead of extension
• Describe a method to investigate the relationship between force and extension for a spring.

  1) Place a heavy weight on the clamp stand to stop it from falling over.

  2) Attach a metre ruler and a spring to the clamp stand, using two clamps and two bosses.

  3) Make sure the top of the spring is at the zero point on the metre ruler.

  4) Also make sure the meter ruler is vertical.

  5) Attach a wooden splint to the bottom of the spring as a pointer, making sure this pointer is horizontal or else the readings will be inaccurate.

  6) Read this initial point on the meter ruler (unstretched length of the spring).

  7) Hang a 1N weight on the spring using a hook.

  8) Read the new position of the pointer on the meter ruler.

  9) Continue adding 1N weights to the spring and reading the position of the pointer.

  10) Calculate the extension produced by adding each weight (subtract the length of the initial unstretched spring from each reading on the meter ruler.

  11) Plot the extension (m) to the weight (N) on a graph => linear, directly proportional relationship
• What happens if we add too much weight to the spring?

  - we have exceeded the limit of proportionality
• What is the limit of proportionality?


  The point at which extension is no longer directly proportional to force
• How can we calculate the force required to extend the spring from the graph?

  F = ke

  1. Workout the spring constant of the spring by dividing the weight by the extension.

  2. Multiply the spring constant by any extension (m) to calculate the force required to extend the spring by that same number of meters.
• what are elastic materials 


  materials that will always return to their original length and shape if we remove the forces acting on them
• Example of inelastic material 


  certain polymers
• what is the relationship between the force and the extension

  they are directionally proportional
• how is the limit of proportionality identified 


  graph will start to curve upwards