Speed is everywhere - from the speed restriction on the road to the time taken for a snail to cross a path!
The word speed is descended of the old english word sped, originally meant "prosperity, successful outcome, ability, or quickness."
Speed is the rate of motion, or equivalently the rate of change in position, many times expressed as distance d travelled per unit of time t.
The average speed v of an object may be calculated by dividing the distance s it has travelled by the time t taken to do so, and may be expressed as:
v = s/t
Speed is a scalar quantity with dimensions distance/time and in which direction of motion is unimportant.
The SI derived unit for speed is meters per second (symbol m/s).
A common derived unit for speed is Kilometres per hour (American : kilometers per hour).
The km/h is the worldwide most commonly used speed unit on car speedometers and road signs. It is far more common than the proper SI derived unit of speed, m/s.
In the United Kingdom, United States and various other nations a common unit used for speed is Miles per hour(MPH).
In nautical and aeronautical applications it is usually user the knot as a unit of speed: one knot is one nautical mile (or nautimil) per hour.
The speed is measured with speedometers.Vehicles often have a speedometer to measure the speed.
Examples of different speeds
- Speed of a common snail = 0.0036 km/h (0.0023 mph)
- speed of sound in air is 343 m/s ( MACH ) , and 1500 m/s in water
- speed of light in vacuum (symbol c): c=299,792,458 m/s