# Forces 3b

• Forces 3b
• 8a) Define the term, 'elastic':
• Something that will return to its original shape after being stretched.
• 8b) What happens to energy when work is done on an elastic object by a stretching force?
• Elastic potential energy is stored in the object as the object is stretched, when released the energy changes to kinetic and a little heat.
• 9) How do you calculate extension from a length?
• Extension=current length-original length.
• 10) Describe how a spring extends in terms of the forces acting upon it:
• As the force on the spring increases, the extension increases, as it is directly proportional as long as it has not exceeded its limit of proportionality, according to Hooke's Law. On a graph, the line would be straight with a positive gradient.
• 11a) What is 'Spring constant'?
• The amount of force per unit of extension to extend a spring.
• 11b) How do you calculate the extension using the Hookes law formula?
• Force(N)=Spring constant(N/m)*extension(m)
• 12) Describe the force-extension graphs for a spring, a rubber band and a polythene bag:
• Spring, straight positive gradient until limit of proportionality.
• Rubber band is curved, the force doubles, the extension more than doubles.
• Not directly proportional, stretches slowly to begin with, then very quickly (opposite to rubber band)

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