2.1 Speed & Average Speed
Speed
Speed is how fast you are going and how far you travel in a certain time.
Distance travelled per unit of time is known as speed.
The above equation is used when the object is moving at a constant speed.
Speed is a scalar quantity because it has magnitude, but it does not have a direction.
Distance is measured in metres (m), time is measured in seconds (s), so speed is measured in metres per second (m/s).
Worked Example
If a card of length 8 cm attached on the top of a trolley passes through the light-gate in 0.2 s. Calculate the speed of the trolley.
Speed =distance travelledtime taken=8 cm0.2 s=40 cm/s
Other Units for Speed
The SI unit for speed in science is metres per second (m/s), but there are others that are used in everyday life.
- kilometres per hour (km/h)
- Miles per hour (miles/h or m.p.h.)
Average Speed
Average speed can be calculated by dividing the total distance travelled by the total time taken. It is defined as
The total distance travelled divided by the total time taken is called average speed.
The above equation is used when the speed of the object varies at different directions.
- An athlete swims from the north end to the south end of a 50.0 m pool in 20.0 s and makes the return trip to the starting position in 22.0 s. What is the average speed for the roundtrip?
