Changing speed
Motion
There are four types of motion:
- rotary
- linear
- oscillating
- reciprocating
Rotary
Rotary motion moves in a complete circle, eg a wheel turning.
Rotary motion can be measured by counting how many times a circle is fully completed over a set period of time, commonly measured in revolutions per minute (rpm).
Example
A cyclist pedals, rotating the bike wheel 18 times in 15 seconds. Calculate the rotational speed.
Rotational speed = number of revolutions ÷ time
= 18 ÷ 15 = 1.2 revolutions per second
Question
A cyclist in a spinning class rotates their bike wheel 12 times in 5 seconds. Calculate the rotational speed.
Rotational speed = number of revolutions ÷ time
= 12 ÷ 5 = 2.4 revolutions per second
Linear
Linear motion moves in a straight line, eg a train moving down a track.
The speed in which an object travels is measured by dividing the distance travelled by the time it takes.
Oscillating
Oscillating motion moves backwards and forwards in part of a circle, eg a pendulum of a mechanical clock. For a motion to be classed as oscillating, the motion must be repetitive.
This motion is measured in oscillations per second or minute.
Reciprocating
Reciprocating motion moves backwards and forwards in a straight line, eg a piston or pump.
This motion is also measured in oscillations per second or minute.
