Topic 15 force and matter

• To change the shape of an object, two forces need to act together. Two forces can bend, stretch or compress an object.
• an elastic band stretches if it is pulled at both ends
• A spring compresses if it is pushed at both ends.
• One force will pull, push or rotate an object.
• Elastic distortion is


  A temporary change in the shape of an object
• Elastic distortion means that when the forces are removed from the object, it goes back to its original shape.
• Inelastic distortion?


  permanent change in the shape of an object.
• linear relationship between force and extension example?

  If an object is elastic (like a spring), the extension is directly proportional to the force applied.
• Linear relationship will only work until object reaches limit of proportionality(wont return to original length)
• non-linear relationship between force and extension.


  Beyond the limit of proportionality, the graph of force against extension is no longer a straight line.
• Linear relationship has straight line on graph between force and extension
• An equation to describe linear elastic distortion works for compression and extention of elastic objects
• Force(N) = spring constant(N/m) × extension/compression(m)
• To find the extension of a spring, subtract the original length of the spring from the final length.
• The greater the spring constant(measure of stiffness of spring)of a spring, the stiffer the spring.
• Spring constant is found using equation and...

  gradient of the graph of force against extension.

  
• The work done in stretching a spring can be calculated with equation which only works if you don't go beyond the limit of proportionality.
• Work done in stretching a string

  Energy transferred in stretching(J)= 0.5 × string constant(N/m) × extension^2 (m)