Sectieoverzicht
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In this course you will learn about:
- The difference between the metric and imperial systems.
- The different units of length.
- How to convert from one metric unit of length to another.
- How to compare various metric lengths.
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Introducing the metric system
Can you define what the metric system is?
Simply put, the metric system measures distance, volume (capacity) and mass based on the decimal systems and using powers of 10. The base units of the metric system are as follows:
- Distance: metres (m)
- Volume: litres (l)
- Mass: grams (g)
However, for very large, or small measurements, there are larger or smaller units of measure which are derived from the base units. We will cover more on this shortly! -
Did you know?
The metric system is used world-wide with the exception of three countries! Can you identify the three countries by their flags below?
The USA, Liberia and Myanmar are the only countries not to use the metric system of measurement. They make use of the imperial system. Countries like the United Kingdom and Canada use both the metric and imperial systems.
The image below reflects the different units of measure used in the metric and imperial systems respectively.
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Now that you have an understanding of what the metric system is, let's explore the units of length.
What is length?
Length measures how long something is from one end to the other end. Here are the common metric units of length from smallest to largest (these should be familiar to you having watched the previous video!):- Millimetre (mm): a millimetre is the smallest unit and will be used to measure the length of very small objects, for example beads and screws. Most rulers will display millimetres
- Centrimetre (cm): centimetres are the next smallest unit and can also be found on a ruler
- Metre (m): metres are the base unit. Common examples of a measurement using metres include the 100 m sprint, 400 m hurdles and the 800 m track race
- Kilometre: kilometres are used to measure longer distances, for example the distance from Dar es Salaam to Blantyre is 1772 km (rounded up)
Earlier you read that the metric system is based on decimals and the power of 10. But what does that mean?
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What is the relationship between the different units?
Let's unpack this.
Now, let's take this a step further! Sometimes you will need to convert a unit measurement that you have been given, into another unit. How would you go about that?
To convert from larger to smaller units you will multiply by the relevant power of 10:
To convert from smaller to larger units, you will divide by the relevant power of 10:
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Converting units
Mustafa is planning to run a 5 km race. In order to prepare for the race, he has been running each day. At the end of the first week, he runs 575 m without stopping. He tries to figure out how that translates in kilometres so he converts 575 metres to kilometres. How many kilometres are equal to 575 metres?Sometimes when you convert metric units you don’t have a whole number answer. When this happens, you end up with an answer that is a decimal.
We said earlier that:
But what happens if we aren't working in numbers rounded like the above? Let's explain this by way of example:
- 1 mm = ? cm
- Since you are converting a smaller unit to a larger unit, you are going to divide. There are 10 mm in one centimetre, so you are going to divide 1 by 10. You are dividing 1 whole into 10 parts
- 1 mm = (1 ÷ 10) cm
- 1 mm = 0.1 cm
The same principle will apply when converting cm to m:- 1 cm = (1 ÷ 100) m
- 1 cm = 0.01 m
...and m to km:- 1 m = (1 ÷ 1000) km
- 1 m = 0.001 km
Let's now go back to the word problem about Mustafa and his race preparation!- What is 575 m in km?
- 575 m ÷ 1000 = 0.575 km
- Mustafa can run 0.575 km without stopping. He has a way to go before he can run the full 5 km without stopping!
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Metric length comparisons
Rehema wants to build a doghouse. She has a few long pieces of wood. Her instructions say that she needs to cut one of the boards in to a piece that is 200 centimetres long, but she only has a metre stick. She wants to figure out if she can measure the entire length using only the metre stick. How can she compare the 200 cm to the metre stick?
The first step in tackling this problem is to decide what unit of measure you would like to use? Metres or centimetres? For this example we will use m.
- Convert cm to m: 200 cm ÷ 100 = 2 m
- Compare the measurements: 2 m > 1 m measurement stick
- Rehema can measure 200 cm with the metre stick, but she would need to use the metre stick twice.
Now complete the following online activities. Be sure to click on the 'Challenge me' button once you've completed the first activity!
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Summary
[edit: the other courses don't have summaries, but I feel it works fine here]
In this course you were introduced to the metric system, which is the most common form of measurement used worldwide.
Attention was then focused on the different units of length i.e. kilometres, metres, centimetres and millimetres. Comparisons between these units of measure were explained and how to convert between these different units was explored.
In closing, watch the video below which sums up what was covered in this unit of study.
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