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# Unit of speed

The SI unit of speed is metres per second $(\text{m/s})$.

Kilometres per hour ($\text{km/h}$) or miles per hour (in the US and UK) are commonly used units in everyday life.

\begin{align*}1\text{ h}&=3600\text{ s} \\1 \text{ km}&=1000\text{m}\\ 1\text{ m/s} = \frac{1/1000 \ukm}{1/3600 \text{ h}}&=3.6 \text{ km/h} \\1\text{ km/h}&\approx 0.28 \text{m/s}\end{align*}

The table shows the approximate speeds of different movements.

m/s km/h
World record for fastest snail 0.003 0.009
Average walking speed 1 3.6
Cruising speed of passenger plane 250 900
Speed of sound in air 340 1,225
Speed of light in vacuum 300,000,000 1,000,000,000
The world record for the fastest snail in a snail race is 0.003 metres per second.