Physical quantities and units
Section: Physical Quantities and Units | Syllabus: Cambridge AS Level Physics (9702)
Physical Quantities
A physical quantity is a property of an object or phenomenon that can be measured.
Every physical quantity consists of two parts: a numerical magnitude and a unit.
A number without a unit has no physical meaning in this context. For example, saying a length is "5" doesn't tell us if it's 5 meters or 5 kilometers.
Common Estimates
Candidates are expected to make reasonable estimates of physical quantities. Here are some common reference values:
| Quantity | Reasonable Estimate |
|---|---|
| Mass of an adult | 70 kg |
| Height of an adult | 1.7 m |
| Mass of an apple | 100 g (0.1 kg) |
| Thickness of a sheet of paper | 0.1 mm |
| Speed of sound in air | 330 m s^-1 |
| Weight of an adult | 700 N |
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