Lever calculations

What the Activity is for

The purpose of this activity is to engage the pupils in making calculations based on levers. These can be hard to do, particularly since they involve four variables.

What to Prepare

• two diagrams
• a simple example or two to calculate

What Happens During this Activity

Talk through what you are doing as you perform a simple calculation, following the logic of the diagram provided:

• Calculate one moment.
• Calculate the opposing moment.
• Compare these two moments.

Here is a second sequence, that reduces the algebraic demand:

• Calculate the change in one energy store.
• Calculate the change in the second energy store.
• Compare these two changes.

This sequence reduces the algebraic demand and in any case emphasises the physics – you cannot get out more than you put in – only go for a trade-off! If you reduce the force, then you'll gain in distance (we can be a bit careless here – similar triangles ensures that this can be either distance moved or length to pivot). We recommend that you are a bit inflexible here, insisting on a clear and clearly reported logic in the calculations. You might emphasise these calculations as a kind of argument. It is not only getting the right answer that matters, but how reliably the evidence supports the case. This is only obvious if you take the trouble to lay out the argument carefully.