The measure of how fast motion can take place is the speed. Speed can be defined as the distance traveled by a body in unit time.

Speed = Distance traveled / time taken

Its SI unit is **metre per second** which is written as ms^{–1}. The other commonly used unit is km h^{–1}.

1 km/h = 1000/(60 × 60) m/s

= 5/18 m/s

**Example:** An object moves along a rectangular path of sides 20 m and 40 m respectively. It takes 30 minutes to complete two rounds. What is the speed of the object?

Distance traveled = 2 × 2(20 + 40) m

= 240 m

time taken = 30 minutes = 30 × 60 s

= 1800 s

Speed = 240/1800 m/s = 4/30 m/s