HOOKE'S LAW

3 marks · Normal

Rubber bands are often used to hold objects together. When you stretch a rubber band, you notice that the extension does not increase evenly as you add more force.

(a)

Explain how the force-extension graph for a rubber band would look different to the graph for a metal spring.

[2 marks]

(b)

Give one reason why a rubber band does not obey Hooke’s law.

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) The force-extension graph for a rubber band is a curve, not a straight line. The extension does not increase proportionally with force. For a spring, the graph is straight with a constant slope at first. · must show Curve for rubber band, Straight line for spring, States difference is proportionality/linearity

(b) The rubber band does not have proportional extension; it is not directly proportional to force, so does not obey Hooke’s law. · must show States extension is not proportional to force

Common mistakes: Thinking rubber behaves same as metal spring

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Mentions that rubber band graph is a curve/not straight line, not directly proportional.

B2 (a) · 1 mark · States spring graph is a straight line/proportional at first (for comparison).

B3 (b) · 1 mark · Gives reason: extension is not proportional to force for a rubber band.

Worked solution

(a) The force-extension graph for a rubber band is a curve that is not a straight line. This means the extension does not increase evenly as more force is applied.

For a metal spring obeying Hooke's law, the force-extension graph is a straight line at first, showing proportion.

(b) A rubber band does not obey Hooke's law because the extension is not directly proportional to the force.