Motion, Forces and Energy
Speed, Velocity and Acceleration
Cambridge IGCSE Physics
Speed
Speed is the distance travelled per unit time.
speed = distance travelled / time takenv = s / t
| Quantity | Symbol | Unit |
|---|---|---|
| distance | s | m |
| time | t | s |
| speed, velocity | v | m/s |
Rearranged: s = v t, t = s / v.
Average speed
average speed = total distance travelled / total time taken
- Use the total distance travelled and the total time taken for the whole journey, including any time at rest.
- Rearranged: distance = average speed × time taken.
Velocity
Velocity is speed in a given direction.
Acceleration
Acceleration is the change in velocity per unit time.
acceleration = change in velocity / time takena = Δv / Δt
- Rearranged: Δv = a Δt, Δt = Δv / a.
- Change in velocity = final velocity − initial velocity.
- Unit of acceleration: m/s2.
Deceleration
- Deceleration is the decrease in velocity per unit time.
- A deceleration is a negative acceleration: in a = Δv / Δt, Δv is negative, so a is negative.
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