A unit of measurement describes one unit of a quantity. Units of measurement can be imperial or metric. They can be converted using conversion factors.
Part of MathsGeometry and measure
Speed is a measure of how fast something is travelling, or how fast something can be done.
The speed of an object is how far the object travels in one unit of time. The formula for speed is:
\(\text{speed} = \frac{\text{distance}}{\text{time}}\)
The most common units of speed are metres per second (m/s), kilometres per hour (km/h) and miles per hour (mph).
These are examples of compound units – an amount that is measured using two or more other measures.
In a typical car journey the speed of the car will change. The distance divided by the time will calculate the average speed of the car.
A car travels 120 miles in 2 hours and 30 minutes. Calculate the average speed of the car in mph.
\(\text{Average speed} = \frac{\text{distance}}{\text{time}}\)
The units of speed are miles per hour so the time must be in hours.
There are 60 minutes in one hour. 30 minutes is half an hour.
Overall time for the journey is 2.5 hours.
\(\text{Average speed} = \frac{120}{2.5}\)
The average speed is 48 mph.
The formula for speed can be rearranged to calculate the time taken or the distance travelled.
\(\text{Distance} = \text{speed} \times \text{time}\)
\(\text{Time} = \frac{\text{distance}}{\text{speed}}\)
Laura walks 17 km at an average speed of 4.25 km/h. Calculate how long it took her to complete the journey.
\(\text{Time} = \frac{\text{distance}}{\text{average speed}}\)
\(\text{Time} = \frac{17}{4.25}\)
Time = 4 hours (the units of speed are km/h so the time is measured in hours)