3Turn-7

Outcomes

• Pupils can sketch the shape of Force verses Extension graphs for helical springs

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

AFL Talk partners

• Why might it be useful to know how stretchy things are?
• Give each pupil spring to promote ideas – CARE NOT TO BREAK!
• Discuss ideas as a class – feedback from one person in pair

Main Body of Lesson

Powerpoint (Hooke's Law L1) and experimental worksheet (Hooke's Law notes) available in shared area

Investigate springiness!

• Demo experimental set up
  • Make sure ruler is clamped vertically and pointer sits nicely against the ruler.

• Highlight safety points - safety glasses and the top loop of spring should be wound with string to stop it from unwinding (only if they are taking it past the elastic limit)

The students will carry out a force extension graph for a spring.

• Discuss variables
  • What are we changing? - The mass
  • What are we measuring? - The length of the spring
  • What are the controls? - Same spring etc
  • From changing the mass and measuring length how can we calculate force (F=ma) and extension (stretched length – equilibrium length)
  • What is the equilibrium (original)length of the spring and why de we need to know this?
  • How do we take this into account when collecting data

• Discuss precision

What is it? What is the smallest scale division on our ruler? Highlight importance of measuring to this level of precision when collecting data

Students get on with collecting data

• GOGGLES NEEDED!
• Take spring up to elastic limit – approx. 0.8kg
• Beyond 0.8kg can be done as a class towards the end of the lesson

Plot graph of force against extension

• Display example axis Force - y axis, Extension - x axis
• Make a conclusion

Comment on the shape of the best fit line, try to describe the pattern which appears. Have you found any simple rule for springs? What happened to the extension when you doubled the load? And three times? Can you work out the gradient? What does this gradient mean? What happens when large loads are added to the spring? (Complete a class demo of this and allow students to write down the data)

Pack all equipment away

Plenary

Condensing the lesson - What is the most important thing you have learnt today?

Homework

Read P 60-61 and answer questions

Additional Information

Resources Required

Class set - experiment on force vs. extension of spring.

• Students will need to support a ruler vertically and will need some sort of pointer
• Springs, rulers, clamp stands, masses

Safety/Hazards

Goggles to be worn during all stretching activities due to the chance of something pinging off 
Ensure pupils do not flick elastic bands at one another or across the room! 
Mass may fall off and fall on feet - ensure pupils stand during practical 
Weigh down the clamp stand to prevent any tipping