Kinematics
This note covers speed, velocity, acceleration, graphical analysis of motion, displacement calculations from velocity-time graphs, and free-fall motion under gravity, aligned with O-Level Physics learning outcomes.
Summary Table
| Topic | Definition | Formula | Unit | Notes |
|---|---|---|---|---|
| Speed | Scalar quantity; how fast an object moves. | Average speed = Distance travelled / Time taken | m/s | - |
| Velocity | Vector quantity - speed with direction. Velocity is the rate of change of displacement | Average velocity = Displacement / Time taken | m/s | Can be positive or negative depending on direction. |
| Acceleration | Rate of change of velocity with time. | a = Δv / Δt | m/s² | Uniform acceleration: constant change; Non-uniform: variable change |
| Displacement-Time Graphs | Graph showing displacement vs time. | Slope = Velocity | - | Here’s an explanation of velocity-time graphs:
|
| Velocity-Time Graphs | Graph showing velocity vs time. | Slope = Acceleration; Area under graph = Displacement | - | Here’s an explanation of velocity-time graphs:
|
| Displacement from Velocity-Time Graph | Displacement calculated from area under velocity-time graph | Rectangle: v × t; Triangle: 1/2 × base × height; Trapezium: 1/2 × (b1 + b2) × h | m | Here’s an explanation of velocity-time graphs:
|
| Free Fall | Motion under gravity only, ignoring air resistance. | v = u + at; s = ut + 1/2 at²; v² = u² + 2as | m/s² for a, m for s, m/s for v & u | g ≈ 10 m/s² (or g = 9.81 m/s²); u: initial velocity, v: final velocity, a: acceleration, s: displacement, t: time |
- ⚠️ Speed and velocity are the same—velocity has direction, speed does not.
- ⚠️ Acceleration only occurs when speeding up—it also occurs when slowing down.
- ⚠️ Area under velocity-time graph is not displacement—it actually represents displacement.
- ⚠️ Free fall only applies to objects dropped from rest—it applies to all objects moving under gravity.
- 👉 Always include units in calculations.
- 👉 Use the correct formula depending on the known quantities.
- 👉 Interpret graphs carefully; check slope and area meanings.
- 👉 Memorize g ≈ 10 m/s² for O-Level free fall problems.
- 👉 Practice drawing and reading displacement-time and velocity-time graphs.