Speed, distance & time

Description

Speed, distance and time are linked by a single formula. Use the triangle to rearrange for whichever quantity you need.

$$\text{Speed} = \frac{\text{Distance}}{\text{Time}}, \quad \text{Distance} = \text{Speed} \times \text{Time}, \quad \text{Time} = \frac{\text{Distance}}{\text{Speed}}$$

Memory aid: cover up the quantity you want in the triangle: $$\boxed{D} \div \boxed{S \times T}$$

Example: A car travels 240 km at 60 km/h. How long does it take? $$\text{Time} = \frac{240}{60} = 4\text{ hours}$$

Units must be consistent: if speed is in km/h, time must be in hours to get distance in km. Convert minutes to hours by dividing by 60.

Average speed is total distance divided by total time — not the mean of two speeds.

Common error: calculating average speed as $\frac{v_1 + v_2}{2}$ when the two speeds are for different distances. Always use total distance ÷ total time.

Links

Compound units Speed time graphs