Numeracy Skills
in D&T
MEASURING LENGTH & PERIMETER
1D (Single-dimension) Measurements
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Numeracy Skills
Why is this relevant to me?
Why is this relevant to me?
Before they can calculate complicated 2D areas or 3D volumes, a person needs to be able to measure 1d lengths accurately.
You will use this skill every time you have a practical making lesson in D&T.
There are different 'scales of measurement' in use across the world.
We will try to teach you the difference between them but....it is essential that you are able to read and understand the metric scale first.
You will recognise these as millimetres, mm and centimetres, cm.
Consider the following tape measure. Slide it along to see the two scales one along the top, one along the bottom.
The top scale is metric, the bottom scale is imperial (an older system based on strange and often arbitrary fractions).
Metric scales of measurement explained
Metric scales of measurement explained
Metric units are based upon constant, predictable divisions of 10 between each scale.
Imperial units are much harder to remember because they are sub-divided into un-even fractions. To remind yourself of fractions, have a look at this page here.
Comparing the magnitude (size) of different units
Comparing the magnitude (size) of different units
Sometimes it is really hard to visualise how large one unit is compared to another. This 'unit conversion tube map' might help you do this.. You can also use it to convert values directly.
Time to test your measuring skills...
Time to test your measuring skills...
What is perimeter?
What is perimeter?
Perimeter is used in all sorts of scenarios in real life from construction through to catering and onto dressmaking.
Use the following videos to help you understand the following topics.
Perimeter Explained
Circles Area/Circumference Explained
Consider a person trying to unroll a roll of chain link fencing to protect their chickens from foxes.
How do they know how much fence to buy?
They need to calculate the perimeter surrounding the chicken coup. This will be the total length of the fence needed.
How to use BODMAS correctly when using a calculator?
How to use BODMAS correctly when using a calculator?
Activity 1.2 Perimeter of simple squares & rectangles
Activity 1.2 Perimeter of simple squares & rectangles
Remember to use brackets correctly AND enter your units in the method.
Activity 1.3. Perimeter of right-angled & isosceles triangles
Activity 1.3. Perimeter of right-angled & isosceles triangles
Remember to use brackets correctly AND enter your units in the method.
Activity 1.4. Perimeter of simple squares & rectangles - mixed, decimal units
Activity 1.4. Perimeter of simple squares & rectangles - mixed, decimal units
Remember to use brackets correctly AND enter your units in the method. Watch out for the different units. The calculator will account for units automatically (as long as you enter them correctly). You may wish to convert them yourself so that they are entered into the method as the same unit.
What is Pi?
What is Pi?
Pi is a number that NEVER changes. It represents the number of times the diameter of a perfect circle can fit inside its circumference (perimeter). It pops up all over the place in mathematics and is a really useful thing to remember. But how do we PROVE that pi is 3.14? Have a look below.
How do we find circumference or diameter , knowing the π relationship and only one of the values?
How do we find circumference or diameter , knowing the π relationship and only one of the values?
Remember that
diameter = radius x 2 or
radius = diameter / 2.
In your questions, you may be given either and have to work with what you've got.
Activity 1.5. Perimeter (circumference) of circles
Activity 1.5. Perimeter (circumference) of circles
Pay attention to the questions. You will not always be given the same value. You will need to be alert for changing values between radius, r and diameter, ø. Remember to use brackets correctly.
Dish size and lining calculator
Dish size and lining calculator
This little tool will help you work out what size dish to use to fit a recipe for a jug capacity and the minimum amount of paper needed to line the dish. You can choose from what you've got available in your cupboard based on how deep the dish is. To fully understand this tool, you will need to learn about the volume of cylinders.
Printable 'Length and Perimeter' Practice Worksheets
Printable 'Length and Perimeter' Practice Worksheets
Full walkthrough lessons.
What is Pythagoras's Theorem?
What is Pythagoras's Theorem?
Named after the Greek philosopher Pythagoras (who didn't create it but popularised it), this helps us find a missing side length in a right-angled triangle as long as two other side lengths are known. BEWARE - This ONLY works for RIGHT-ANGLED TRIANGLES!
Calculate the length of an arc
Calculate the length of an arc
If you know the radius of rotation, you can calculate the length of an arc (the distance travelled by a point as it rotates about a centre).
We do this using an alternative method of calculating angle, called radians. Radians are often used by engineers and mathematicians.
What are sine, cosine and tangents?
What are sine, cosine and tangents?
'Sine' and 'Cosine' values can be thought of as the coordinates of a point that sits on a circle in relation to the centre of the circle. 'Sine' represents the X coordinate and 'Cosine' represents the Y coordinate. They are both unitless properties (they don't carry units).
A 'tangent' can be thought of as the slope of the projected line as it intersects the circle. Since it is always the sine divided by the cosine (i.e. a fraction or division) it too is unitless. If you drew a line from the circle at the end of the X axis until it 'hits' the projected line, that would be the tangent.
All three properties are essential to understanding trigonometry and the 'SOH-CAH-TOA' relationship.
Using the sine and cosine rules
Using the sine and cosine rules
Where triangles are concerned, if you know 2 values (angles or side lengths), then you can find a third. There are two 'rules' (i.e. expressions) for doing this; the 'Sine rule' and the 'Cosine rule'. Depending upon what you know (or have been 'given'), then this will determine which of the rules you will need to use.
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