Speed - Think Metric!

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Want to know how fast something is? How quickly it moves and how long it will take to get somewhere? If you know the speed then you can.

speedlimits — Ireland switched to km/h speed limits in 2005

In metric, speed is usually measured in kilometres per hour. The kilometre is a unit of length. Another unit of length, the metre, can be also be used as the basis for speed, as in metres per second. The symbol for kilometres per hour is km/h, and the symbol for metres per second is m/s. Metres per second are mostly used for more scientific usage, and we really only need to worry about km/h here, although it is interesting to note that average human walking speed is around 1 metre per second, which makes it very easy to remember, equivalent to 3.6 km/h — multiply metres per second by 3.6 to get kilometres per hour, or divide km/h by 3.6 to get m/s.

Here are some example speeds:

Speed	Typically found
0 km/h	Stationary objects, not moving, parked car
1 m/s, 3.6 km/h	Average human walking speed
20 km/h	Easy cycling speed on a bicycle
50 km/h	Typical car speed on residential roads or busy city roads
80–90 km/h	Vehicle on main road, travelling reasonably fast
100–120 km/h	Fast car on motorway, typical speed of a cheetah running, freight trains
200–300 km/h	High speed train
360 km/h	Racing car
800-1000 km/h	Airliner cruising speed
340 m/s, 1224 km/h	The speed of sound at sea level on Earth (it varies according to altitude, air pressure, and in space the speed is zero), also known as Mach 1
1228 km/h	Current world land speed record, held by the ThrustSSC car (Mach 1.016)
2012 km/h	The fastest speed recorded by the Concorde aircraft in 1996
1000 m/s, 3600 km/h	Speed of a bullet from a rifle
26 000 km/h	Re-entry speed of the space shuttle
40 320 km/h	Earth’s escape velocity
299 792 458 m/s, 1 079 252 849 km/h	The speed of light, which we can approximate to 300 million metres per second, or 1 billion kilometres per hour