Study of motion
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6. Instantaneous speed

Units of speed:


If we look at the equation for average speed, we can deduce that speed is always given in units of length divided by units of time.

According to the SI, the unit of length is the metre and the unit of time is the second. So, the SI unit of speed is metre per second (m/s), although speed is also given in other units, like km/h or cm/s.

Instantaneous speed
Figure 8.6

During a typical trip, your car will undergo a series of changes in its speed. If you were to inspect the speedometer readings at regular intervals, you would notice that it changes often.

The speedometer of a car reveals information about the instantaneous speed of your car. It shows your speed at a particular instant in time.

Instantaneous speed, v, or just speed, is the speed of an object at a particular moment.

The instantaneous speed of an object is not to be confused with the average speed.

Average speed is a measure of the total distance travelled in a given period of time; it is sometimes referred to as the distance per time ratio.

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