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# Definition of speed

Speed is the distance travelled per unit of time. It is a scalar quantity.

If you run at 12 km/h, you will cover 12 km in one hour, 6km in half an hour, 24 km in two hours, etc.

Speed is written $S$ or $v$. It is the ratio

$$\Tgreen{\text{speed}} =\frac{\Tred{\text{distance}}}{\Tblue{\text{time}}}.$$
• A car drove 20 km in 20 minutes (1/3 hour). Its speed was $$\frac{\Tred{20\ukm}}{\Tblue{20\umin}} =\frac{\Tred{20\ukm}}{\Tblue{1/3\uh}} = \Tgreen{60\ukmph}.$$
• A plane flew at 1000 km/h for 3 hours. It covered $$\Tgreen{1000\ukmph}\times \Tblue{3\uh} = \Tred{3000\ukm}.$$
• Paul ran 1 km at a speed of 10 km/h. The run took him $$\frac{\Tred{1\ukm}}{\Tgreen{10\ukmph}} = \frac{\Tred{1}}{\Tgreen{10}}\Tblue{\uh} = \frac{\Tred{1}}{\Tgreen{10}} \Tblue{60} \Tblue{\umin} = \Tblue{6\umin}.$$
The ThrustSSC holds the record for the fastest speed ever recorded by a car $(1228 \ukmph)$