Physics Foundations
Every physics answer stands or falls on its units. Nail SI units and prefixes, learn to estimate sensibly, and tell scalars from vectors before it costs you marks.
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Physics Foundations ⚖️
A number in physics means nothing without its **unit**. "5" could be 5 metres, 5 seconds or 5 newtons. This short module locks down the basics that every other topic relies on: **units and prefixes**, **sensible estimates**, and the difference between a **scalar** and a **vector**.
SI units and prefixes 📏
Physics uses agreed **SI units**. The key base units are the **metre (m)** for length, the **kilogram (kg)** for mass, the **second (s)** for time and the **ampere (A)** for current. **Prefixes** scale a unit up or down: **kilo** means x1000, **centi** means divide by 100, **milli** means divide by 1000, and **micro** means divide by 1 000 000.
Match each prefix to what it does
- kilo (k)
- centi (c)
- milli (m)
- micro
- Multiply by 1000
- Divide by 100
- Divide by 1000
- Divide by 1 000 000
Convert the units
An interactive activity.
Scalars and vectors 🧭
Physical quantities come in two kinds: - A **scalar** has **size (magnitude) only**: mass, speed, distance, energy, temperature, time. - A **vector** has **size AND direction**: velocity, displacement, force, acceleration, momentum, weight. The direction is the whole point of a vector: 30 m/s means little until you say 30 m/s **north**.
Which are vectors?
Select ALL THREE quantities that are VECTORS (they have a direction as well as a size).
- Velocity
- Force
- Displacement
- Speed
- Mass
- Energy
Mass or weight?
On the Moon your mass is unchanged but your weight is less. Which statement is correct?
- Mass is a scalar (an amount of matter); weight is a vector because it is a force with a direction
- Mass and weight are both vectors
- Mass and weight are both scalars
- Mass is a vector and weight is a scalar
Foundations summary
Physics measurements need the right unit: length in metres, mass in _____, time in seconds. A prefix changes the size, so kilo means times _____. A quantity with size only is a _____, while one with size AND direction is a _____.