Physics
Kinematics & equations of motion — quick study summary
Kinematics is the description of motion without worrying about its cause. The big four 'SUVAT' equations connect displacement (s), initial velocity (u), final velocity (v), acceleration (a), and time (t). They only apply under constant acceleration. Velocity is displacement per second (a vector); speed is its magnitude. Acceleration is rate of change of velocity. Free fall near Earth's surface has a ≈ 9.81 m/s² downward.
Key points
- v = u + at
- s = ut + ½at²
- v² = u² + 2as
- s = ½(u+v)t
- Free fall: a = g ≈ 9.81 m/s²; air resistance ignored in basic problems
Practice quiz
Click each question to reveal the answer.
1. A car accelerates from 5 m/s to 25 m/s in 4 seconds. What's its acceleration?
- 2 m/s²
- 5 m/s²
- 10 m/s²
- 20 m/s²
Answer: 5 m/s²
a = (v − u) ÷ t = (25 − 5) ÷ 4 = 5 m/s².
2. An object falls from rest. How far has it fallen after 2 seconds (g = 10 m/s²)?
Answer: 20 m
s = ut + ½at² = 0 + ½(10)(2²) = 20 m.
3. What's the difference between speed and velocity?
Answer: Speed is a scalar (magnitude only); velocity is a vector (magnitude + direction)
A car going 30 mph round a circular track has constant speed but changing velocity (because direction keeps changing).
Last reviewed: May 2026