Units of length
When measuring the length of something or the distance between
places, you have to choose an appropriate unit of length.
There are four units of length that are used in the metric system.
Metres (m)
Metres are the standard unit of length.
You would measure the length of a floor in metres.
Centimetres (cm) A centimetre is used to measure smaller lengths such as
the height of your school table.
Metres are divided into 100 cm.
Millimetres (mm)
Millimetres are used to measure very small lengths such
as the length of an insect.
Centimetres are divided into 10 mm.
Kilometres (km)
Kilometres are used to measure large distances such as
the distance between two countries.
There are 1000 metres in 1 kilometre.
There are other units of length out with the metric system that are commonly used,
including miles.
Miles are also used to measure long distances. 1 mile is roughly equal to
1600 metres or 1.6 km.
Units of length
What would be the best unit of length to use to measure the following?
The length of a swimming pool
Metres
The width of a fingernail
Millimetres
The distance from Glasgow to
London
Kilometres
The length of a banana
Centimetres
The width of an iPod
Centimetres
The width of a nail
Millimetres
The distance between Ibrox
and Parkhead
Kilometres
The height of Big Ben
Metres
Now try question 1 in your booklet.
Units of length
Each of the units of length that we looked at in the first slide can be
broken down and described using alternative units of length.
We have already seen that there are 1000 metres in a kilometre, and roughly
1600 metres in a mile so we will look at centimetres and metres now.
Metres (m)
There are 100 centimetres in 1 metre.
Centimetres (cm) There are 10 millimetres in 1 centimetre.
How many centimetres are there in 2 metres?
200 centimetres
How many millimetres are there in 50 cm?
500 millimetres
How metres are there in 6 kilometres?
6000 metres
Measuring lengths
There are a number of devices that you can use to measure lengths.
A ruler allows you to measure small lengths in both centimetres (cm) and
millimetres (mm).
The longer lines on a ruler show centimetres.
The smaller lines on a ruler show millimetres.
To measure in metres you can use a tape measure,
a metre stick or a trundle wheel.
To measure in kilometres you can use a car odometer
These are just a few devices that you can use.
Now try question 2 in your booklet.
Measuring lengths
What would be the best device to use to measure the following?
The length of a swimming pool
Trundle wheel
The width of a fingernail
Ruler
The distance from Glasgow to
London
Odometer
The length of a banana
Tape measure
The width of an iPod
Ruler
The width of a nail
Ruler
The distance between Ibrox
and Parkhead
Odometer
The height of a door
Tape measure
Now try question 3 in your booklet.
Using a ruler
Rulers usually show centimetres and millimetres.
As you can see, 1 cm is split into 10 parts called millimetres.
1cm = 10mm
0 cm
1
2
3
4
0 mm
10
20
30
40
This line is 3.5 cm or 35 mm or 3 cm 5 mm.
This line is 4.1 cm or 41 mm or 4 cm 1 mm.
It is vital when measuring something with a ruler that you start at 0.
Using a ruler
What length are these arrows pointing to in cm and mm?
a
b
c
d
e
f
g
h
0 cm
1
2
3
4
0 mm
10
20
30
40
a
0.4 cm, 4 mm, 0 cm 4 mm
e
2.4 cm, 24 mm, 2 cm 4 mm
b
0.8 cm, 8 mm, 0 cm 8 mm
f
2.9 cm, 29 mm, 2 cm 9 mm
c
1.5 cm, 15 mm, 1 cm 5 mm
g
3.6 cm, 36 mm, 3 cm 6 mm
d
2 cm, 20 mm, 2 cm 0 mm
h
4.3 cm, 43 mm, 4 cm 3 mm
Millimetres
In industrial settings, even large objects are measured in millimetres.
This is to ensure that measurements are made very accurately, which
is vital in construction.
Sometimes the success of a project might rely on an object being
123 mm rather than 125 mm.
All car parts are measured
in mm rather than cm.
450 mm
205 mm
Now try questions 4 to 8 in your booklet.
Test yourself
You are now ready to tackle the end-of-topic test in your booklet.
GOOD LUCK!!