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Measuring length and perimeter | Length
measurement facts |
| Summary of perimeter formulae of some special
shapes| Quick quiz |
Measuring length
and perimeter
Length
is a one-dimensional measure. It can be referred to as length, width,
height, thickness, depth, distance, diameter etc. We can measure the
length of curved as well as straight lines.
The
distance around a region, such as a block of land or a lake is its
perimeter. To measure perimeter we can just add the lengths
of the sides or we use formulae that make use of length measurements
relating to the shapes being measured.
Length
measurement facts
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LENGTH
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SI
Base unit: metre (m)
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10
millimetres (mm)
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= 1 centimetre (cm) |
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10
centimetres (cm)
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=
1 decimetre (dm) |
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10
decimetre (dm)
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=
1 metre (m) |
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1000
millimetres (mm)
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=
1 metre (m) |
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100
centimetres (cm)
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=
1 metre (m) |
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1000
metres (m)
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=
1 kilometre (km) |
Summary
of perimeter formulae of some special shapes
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Perimeter
of a square = 4 x l
where 'l' is the side length of the square
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Perimeter
of a rectangle = 2 x (L + W)
where 'L' is the 'length' and 'W' is the width of the rectangle
The
perimeter is equal to L + W + L + W, which is twice (L + W)
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Example
1: Measuring the perimeter of an object.
Due to complaints of wayward tennis balls from neighbours, the local
tennis court needs its fence replaced. If the court and surrounds
is 55 metres long and 23 metres wide, what is the perimeter which
needs to be fenced?
| Setting
Out |
Thinking |
Perimeter
= 2 x (l + w)
= 2 x (55m + 23m)
= 156 metres |
To
find the perimeter of a rectangular object I just need to add
each side length. This is equivalent to taking 2 times the length
and width of the object.
I need to make sure my answer is complete by including the measurement
units, which in this case are metres.
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Circumference of a circle |
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We usually call the perimeter of a circle the circumference
of a circle.
'r' is the radius of
the circle which is the distance from the centre of the
circle to the edge of the circle.
 ,pronounced
as 'pi', is a special number which is approximately equal
to 3.142. Because pi is often used in calculation of circular
measurements there is often a
button on a calculator. |
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Example
2: movie - measuring an odd shaped perimeter.
Stan wants to install an L-shaped pond in his inner city courtyard
garden. He has seen a suitable pond (which is pictured) and wants
to know its perimeter. Find the perimeter of the pond.
Quick
quiz
| 1. |
Express
each measurement in the units indicated: |
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a)
Convert 39 cm to mm |
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b)
Convert 543 m to cm |
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c)
Convert 16790 mm to m |
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d)
Convert 1.44 km to mm |
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| 2. |
Which
measurement is longer: |
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a)
340 mm or 45 cm |
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b)
5009 m or 12 km |
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c)
8.5 m or 7000 mm |
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d)
13000 mm or 1.3 km |
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| 3. |
Calculate
the perimeter of the following shapes: |
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 |
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| 4. |
Calculate
the perimeter of a circular swimming pool if its radius is 1.5
metres. |
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| 5. |
I
have seen a dining room table that I like in a shop and I want
to estimate its length and width to see if it will fit in our
home. Not having a tape measure on hand, I use my palm and work
out that the length is about 18 palms long and 12 palms wide.
If my palm is approximately 10 cm in width, how long and how
wide is the table?
After
I got home I measured the space where the table needed to fit
and realised that the table was slightly too big. To check the
accuracy of my estimate I measured the width of my palm and
found that it is only about 8.5 cms wide, what is a more accurate
measure of the length and width of the table?
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| 6. |
If
the length of a small rectangular suburban house block is 36.5
m and the width is 15.9 m, what is the perimeter of the block?
If
the block is being subdivided by dividing the width of the block
equally in 2, what is the perimeter of each new block?
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To
view the quiz answers, click here.
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©
University of Melbourne
2003 |
is the first letter of the Greek word perimetron which
means 'the measurement around'. It has been used since the times
of the ancient Egyptians. 