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