Outcomes

Pupils can sketch the shape of Force verses Extension graphs for helical springs, metal wires and rubber bands.
Pupils can identify and recall that the initial linear region of a force-extension graph is associated with Hooke's law.
Pupils associate elastic behavior with the ability of a material to recover its original shape after the forces causing deformation have been removed.

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.

Pupils recapping ideas from previous two lessons

Powerpoint (Hooke's Law L3) and experimental worksheet (Hooke's Law notes 3) available in shared area

Hand out wire to pupils

GOGGLES NEEDED!

Pupils wrap the thin wire several times around one of their pencils, then take the other end of the wire and wrap it several times around another pencil leaving at least 5 cm of wire between the two pencils.
Pupils pull carefully and slowly on the two pencils to try and stretch the wire.
The wire should be difficult to stretch and then with additional force it should yield a bit and then break.

Demo force extension experiment for a wire using vernier scale GOGGLES NEEDED!

Collect class data - PASCO plots this quite nicely
Students to sketch graph of force vs extension for a wire from PASCO data
Discuss ideas + come to a conclusion
- Comment on the shape of the best fit line, try to describe the pattern which appears.

Does the wire obey Hooke’s Law?

Summary page in classwork books

Students to look at 3 graph types made over the past 3 lessons
On 1 A4 page – mini sketch of each one with description as to what each shows
- Spring, Elastic band, Wire
- Notes to include discussion on the shape of the graph, if the material obeys Hooke’s Law and if so label the region on the graph
- Use key words – Elastic limit, Hooke’s law, linear, non-linear, directly proportional

- Springs
  - Obey Hooke's law up to point y
  - Beyond this point, the spring is permanently deformed.
  - It will not return to its original length when the force is removed.
  - The graph is directly proportional up to point y

- Elastic bands
  - Do not obey Hooke's law.
  - The graph shows a non-linear relationship as it is curved.

- Metal wires
  - Obey Hooke's law up to the elastic limit.
  - Beyond this point, the wire is permanently deformed.
  - It will not return to its original length when the force is removed.
  - The graph is directly proportional up to the elastic limit

Show how energy is equal to the area under the graph line of a force vs extension graph

Quiz Quiz Trade

Write 3 different questions about the last 3 lessons on 3 different post–it-notes
Write the answers on the reverse side
Circulate the room and find a partner
Ask them one of your questions and let them ask you one of theirs
If you answer correctly you take the post–it-note
The person with the most post–it-notes after 5 minutes wins!