What it shows
Two plates joined at the centre open like a fan to show any angle from 0 to 360 degrees. The scale shows that a right angle is 90 degrees, a straight angle 180 degrees and a full turn 360 degrees, and the arm names each angle as acute, right, obtuse or reflex.
The science
An angle measures the amount of turn between two arms meeting at a point. A full turn is divided into 360 equal degrees. When the coloured sector is opened, the number of degrees swept by the arm is the angle, so the plate works like a protractor you can see turn. Angles less than 90 are acute, exactly 90 is right, between 90 and 180 is obtuse and more than 180 is reflex.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Two paper plates of the same size in two colours
- A protractor
- A sketch pen
- Scissors
- A split pin (optional)
Safety
For this project: An adult must help with scissors for younger children.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut a straight slit from the edge of each plate to its exact centre.
Slide the two plates into each other through the slits so they sit face to face and can rotate.
With the protractor, mark 0, 30, 45, 60, 90, 120, 135, 150 and 180 round half of the rim of the back plate, then turn the protractor over and carry on round the other half to 270 and back to 360.
Turn the front plate so a sliver of the second colour shows: a small acute angle. Turn until the colours split the plate in half: 180 degrees.
Turn to 90 degrees and check with the corner of a book that it is a right angle.
Write the four angle names on the rim in the zones where they apply.
Challenge a friend to set 45 degrees without looking at the scale, then check.
What you should see
The plate shows any angle at a glance and the scale confirms it: a book corner matches 90 degrees and a half-open plate reads 180 degrees.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01How many degrees are in a full turn?
360.
02What do we call an angle of 120 degrees?
Obtuse, because it is more than 90 but less than 180.
03What angle do the clock hands make at 3 o'clock?
90 degrees, a right angle.
04Is 200 degrees acute, obtuse or reflex?
Reflex, because it is more than 180.
Take it further
Use the plate to measure the angles of a triangle cut from card and show they add to 180 degrees.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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