Units of length

1
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.
2
Units of length
What would be the best unit of length to use to
measure the following?
The length of a swimming pool
The width of a fingernail
The distance from Glasgow to London
The length of a banana
The width of an iPod
The width of a nail
The distance between Ibrox and Parkhead
The height of Big Ben
Metres
Millimetres
Kilometres
Centimetres
Centimetres
Millimetres
Kilometres
Metres
Now try question 1 in your booklet.
3
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
4
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.
5
Measuring lengths
What would be the best device to use to measure
the following?
The length of a swimming pool
The width of a fingernail
The distance from Glasgow to London
The length of a banana
The width of an iPod
The width of a nail
The distance between Ibrox and Parkhead
The height of a door
Trundle wheel
Ruler
Odometer
Tape measure
Ruler
Ruler
Odometer
Tape measure
Now try question 3 in your booklet.
6
Using a ruler
Rulers usually show centimetres and millimetres.
As you can see, 1 cm is split into 10 parts
called millimetres.
1cm 10mm
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.
7
Using a ruler
What length are these arrows pointing to in cm
and mm?
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
8
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.
Now try questions 4 to 8 in your booklet.
9
Test yourself
You are now ready to tackle the end-of-topic test
in your booklet.
GOOD LUCK!!