3Turn-8

Outcomes

• Pupils can sketch the shape of Force verses Extension graphs for helical springs, and rubber bands.
• Pupils can identify and recall that the initial linear region of a force-extension graph is associated with Hooke's law.

Specification References

• 1.27 describe how extension varies with applied force for helical springs, metal wires and rubber bands
• 1.28 recall that the initial linear region of a force-extension graph is associated with Hooke's law
• 1.29 associate elastic behaviour with the ability of a material to recover its original shape after the forces causing deformation have been removed.

Starter

Think back to last lesson - AFL

• What did I learn?
• What did I find easy?
• What did I find difficult?
• What do I want to know now?

Gives students the chance to recall what was done last lesson and assess their learning - What were they able to complete easily? What did they find more tricky?

Main Body of Lesson

Powerpoint (Hooke's Law L2) and experimental worksheet (Hooke's Law notes 2) available in shared area

Introduce graph shapes

• Linear, non-linear and directly proportional – notes in books
• What was the spring form last class?
• What do they know about Hooke’s Law as found in homework?
• Sketch graph of this – Discuss region where Hooke’s Law applies
• Define Hooke’s Law and state F=kx

Give students one rubber band between 2

• Ask students to stretch them – GENTLY!
• What do you think the graph for this would look like if we did the same experiment?

Experiment to be done as a class

• Discuss variables – same as last time - force and extension
• Show how to measure extension using two lines on rubber band
• Don’t want the band to break – take data as you add masses and then remove them also.

Analysis

• Plot graph
• Conclusion
  • What do you notice
  • How does the rubber band behave?
  • Does it obey Hooke's law?
  • What can you say about the graph in relation to the 3 graph types discussed earlier?

Plenary

Evaluation of string model

Ask pupils what would happen if you start pulling of opposite ends of the pile of string. What will happen to the behavior of the pile when all the string is eventually pulled straight? Does this help them explain how and why rubber bands behave as they do when stretched?

Ask pupils to discuss if this is a good model? Get them to explain thier answers

Additional Information

Resources Required

String with cross links demo Class set - experiment on force vs. extension of rubber band. Students will need to support a ruler vertically and will need some sort of pointer Rubber bands, rulers, clamp stands, masses

Safety/Hazards

*Goggles should be worn during any stretching activity due to the chance of something pinging off 
*Ensure pupils do not flick elastic bands around the room! 
*Mass may fall off and fall on feet - ensure pupils stand during practical 
*Weigh down the clamp stand to prevent it tipping