1. Motion
Motion is a change in position over time. Speed tells us how fast something moves, while velocity also includes direction. Acceleration is how quickly velocity changes.
2. Newton's three laws
- First law (inertia): an object stays at rest or keeps moving at constant velocity unless a net force acts on it.
- Second law: force equals mass times acceleration (F = ma).
- Third law: for every action there is an equal and opposite reaction.
3. Energy
Energy is the ability to do work. It exists as kinetic, potential, thermal, chemical, electrical and other forms. The law of conservation of energy says energy is never created or destroyed, only transferred or transformed.
4. Waves and light
Waves carry energy from one place to another. Sound is a mechanical wave that needs a medium. Light is an electromagnetic wave and travels through empty space at about 300,000 km per second. Light can reflect, refract (bend) and be split into colours.
5. Electricity
Electric current is the flow of charge, measured in amperes (A). Voltage is the "push" that drives the current, measured in volts (V). Resistance, measured in ohms (Ω), opposes the flow.
Key formulas
| Quantity | Formula | Unit |
|---|---|---|
| Speed | v = d / t | m/s |
| Acceleration | a = (v − u) / t | m/s² |
| Force | F = m × a | newton (N) |
| Work | W = F × d | joule (J) |
| Kinetic energy | KE = ½mv² | joule (J) |
| Potential energy | PE = mgh | joule (J) |
| Power | P = W / t | watt (W) |
| Ohm's law | V = I × R | volt (V) |