Speed
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.
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.
Kilometres per hour is abbreviated to km/h, and metres per second to 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 

360 km/h 

800–1000 km/h 

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 
Reentry speed of the space shuttle 


40 320 km/h 

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 


Wind Speeds
We can measure wind speeds in kilometres per hour. The chart
below shows us what various wind speeds relate to in terms of calm, hurricane,
etc.