E-LearningRate & Speed

Rate A comparison of physical quantities with

time is called rate.

Rate describes how one quantity changes with respect to time.

Rate Examples of rate are number of words

typed per minute, number of heartbeats per minute and number of babies born per hour.

An important rate that you will be studying in this chapter is speed.

It is a comparison length with time.

Speed Speed is defined as the rate of change of

distance travelled.

The speed of an object depends on two quantities:

1. distance (length) moved and;2. time taken

Therefore, speed is a derived quantity.

Speed The SI unit for speed is metre per

second (m/s).

Other common units are kilometres per hour (km/h) and centimetres per second (cm/s).

Speed Typical speeds of different moving

objects

Average Speed An object does not always move at the same speed.

Sometimes it moves faster and sometimes slower.

For example, a bus starts from rest and moves faster. Then it slows down to a stop at a traffic light.

Therefore, it is more useful to measure the average speed than the speed at a particular instant.

Speed equation

Formula triangle for speed:

Average speed: