# SPEED / VELOCITY

#### branchMECHANICS (MOTION)

==Speed== Speed is simply how fast something is moving. To measure the speed of an object we need to know... *The '''distance''' travelled * The '''time''' taken ==Velocity== Velocity is also a measure of how fast something is moving, in a particular direction. Velocity is a '''vector''' meaning it has both a magnitude (size) and direction. The difference is very subtle, but if you were traveling at a constant speed and changing direction, your velocity would technically be changing. The formula for '''average''' speed is: [image:http://i.imgur.com/upt4TR4.png] For instance, if you ran a 100m sprint you could work out your average speed by dividing 100m by the time taken to reach the finish line. The reason this gives us the ''''average speed'''' is because you would have been travelling more slowly at the start of the race and would have been going faster toward the end. Your speed at any given moment in time is the ''''instantaneous speed''''. ===The formula can also be re-arranged to calculate '''distance''' or '''time'''=== [image:http://i.imgur.com/QdXM6KL.png?1] ===If you are given a speed in kmh^-1^ (kilometres per hour) you may have to convert it to ms^-1^ (meters per second) E.g.=== [image:http://i.imgur.com/AYnpklC.png?1] kilometres can be converted to metres by multiplying by 1000. Hours can be converted into minutes by multiplying by 60 and then into seconds by multiplying by 60 again.
Credit: Tristan O'Hanlon, Ben Himme