1. E-Learning
Rate & Speed

2. Rate
A comparison of physical quantities with
time is called rate.
 Rate
describes how one quantity
changes with respect to time.

3. 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.

4. 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.

5. Speed
 The
SI unit for speed is metre per second
(m/s).
 Othercommon units are kilometres per
hour (km/h) and centimetres per second
(cm/s).

6. Speed
 Typical speeds of different moving objects

7. 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.

8. Speed equation
 Formula triangle for speed:
 Average speed: