A shape stays itself when turned
Identify shapes by their straight sides and vertices, not their colour or direction.
Start with the activity ↓Is it still a triangle when its point faces down?
Turn the shape. Its direction changes, but a triangle still has three joined straight sides.
Draw a triangle on paper and turn the paper. Its point faces sideways or down. It may look different, but no line has been added or removed.
A straight part of the boundary is a side. Where two sides meet is a vertex, or corner. Trace the boundary once: a triangle has three sides and three vertices.
A circle has no straight sides or vertices. Size and colour cannot reliably distinguish a circle from a triangle. Look at the boundary instead.
A square has four equal sides and four right-angle corners, like the corner of a sheet of paper. Turning it does not change this. An oblong rectangle also has four right angles. A square is a special rectangle with all four sides equal.
Four sides alone do not make a square. Side lengths and corners also matter. No angle calculation is needed yet: compare with a paper corner and trace the sides.
Listen one paragraph at a time
1 / 5
2 / 5
3 / 5
4 / 5
5 / 5
Now check it yourself
Choose a shape, turn it or change its size. Point to its sides and vertices before and after.
These are closed plane shapes without crossing sides. Turning a shape is different from stretching or deforming it.
Try it away from the screen
Draw shapes and turn the whole sheet. Scissors are not needed. Compare corners using the corner of a sheet of paper.
Can you explain another example?
Check your idea 1
Check your idea 2
Can you explain it in a new setting?
Explain with gestures or a drawing why a turned triangle remains a triangle.
Speak, point or draw on paper. Check whether your own explanation includes these ideas.
Continue reading, or pause here
How does a drawing differ from an object you can hold? Next, explore solids.