IGCSE §1: Forces and Motion · IGCSE
Units
Revision notes on Units for the OCR A-level Physics specification (H556). Free to read, with 3 practice questions in the app.
Physical quantity — something that can be measured, written as a number with a unit. The number on its own means nothing: 5 what?
The units you are expected to know for this specification, and to use without being reminded:
| Quantity | Unit | Symbol |
|---|---|---|
| Length, distance | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Speed, velocity | metre per second | m/s |
| Acceleration | metre per second squared | m/s² |
| Force, weight | newton | N |
| Energy, work | joule | J |
| Power | watt | W |
| Momentum | kilogram metre per second | kg m/s |
| Moment | newton metre | N m |
Unit symbols are case-sensitive. A unit named after a person takes a capital: N for Newton, J for Joule, W for Watt. Written in full it stays lower case — "ten newtons", not "ten Newtons". Writing n for newtons or S for seconds costs marks.
Converting before you substitute — the equations only work in these units. A distance in kilometres, a time in minutes or a mass in grams has to be converted first:
1 km = 1000 m
1 minute = 60 s
1 kg = 1000 g
Example: a car travels 3 km in 2 minutes. Substituting 3 and 2 gives 1.5, which is not the speed in m/s. Converting first gives 3000 m in 120 s, so the speed is 25 m/s. The same arithmetic, a very different answer.
Standard form is worth being comfortable with, because some of these quantities are very large or very small. 3 × 10⁸ is 300 000 000, and 5 × 10⁻³ is 0.005.
3 questions on Units
Reading is not revising. This topic has 3 questions in the app — multiple choice, calculations, and written answers marked against the mark scheme, point by point. Miss one and it comes back later with its options reshuffled, so you have to know it rather than remember where the answer sat.
- Every topic of Edexcel International GCSE Physics (4PH1)
- Flashcards and every equation, linked to the topic it comes from
- Full mock papers in the real paper structure
20 minutes a day is free. No card, nothing to cancel — and the paid version never renews itself either.
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