Writing the formula
The one rung where you write, which is why it comes last. You are not asked to recall an equation: you are asked to get it out of the unit, which is what the first rung taught. If a newton is kilogram-metre per second squared, force cannot be anything but mass times acceleration; if a watt is a joule per second, power is energy over time. The unit is written on the card and the formula is not, so this is answered by understanding rather than remembering — and with no four options to choose from, which is the difference between recognising something and knowing it.
Where this sits
- Comes after
- Quantities, Energy, Circuits
Exercises from this rung
Generated by the app, from easiest to hardest
How fast an energy is being spent
Answer E/t
Why P = E / t. Joule over second, literally. A watt is not an amount of energy but a rate of spending, and mixing the two is what makes an electricity bill unreadable. It comes from “Quantities”.
easierThe speed at which a wave travels
Answer λ·f
Why v = λ · f. Each oscillation is one wavelength long and that many go by each second: the product is metres per second. In air sound always travels the same, so more frequency means less length. It comes from “Waves”.
in betweenHow much the speed changes each second
Answer Δv/t
Why a = Δv / t. Metres per second, divided by seconds again: that is where the square comes from. The delta is not decoration — what gets divided is the change in speed, not the speed. It comes from “Motion”.
harder