S4.9.2 For the adult
Springs and elastic energy
Within its limit, a spring stretches 2 cm under a 1 N weight. How far will a 3 N weight stretch it?
What this chapter teaches
The extension of a spring is proportional to the force, F = k × e, up to the limit of proportionality. The energy stored is ½ × k × e², the area under the force extension line, so doubling the stretch gives four times the energy.
Three questions to ask
There is no one right wording. Listen for the idea.
- What is the extension of a spring, and how do you find it from two lengths?
- Why does double the stretch store four times the energy?
- What happens to the line on the graph at the limit of proportionality?
After the chapter, the learner can
- Use Hooke's law to calculate the extension of a spring
- Calculate the energy stored in a stretched spring
What they copy into their notebook
Extension e = length now − natural length. F = k × e, with e in m, up to the limit. Ee = ½ × k × e². Double e, four times the energy.