Watch carefully. I am going to stand here, then turn to face the door. How much did I turn? Was it a small turn, a quarter turn, a half turn, or all the way round?

Look at the clock on the board too. The two hands at 3:00 make a sharp square corner, just like the corner I turned through. That amount of turn is called an angle.

Watch as the orange ray on the angle-tool makes four different angles. Notice that each one is named by how MUCH the ray has turned, not by how long the rays look.

Right angle (90°)

A quarter turn. The two rays meet at a sharp square corner, just like the corner of your maths book.

Acute angle (less than 90°)

Smaller than a right angle. A narrow, sharp opening, like the hands of a clock just after one o'clock.

Obtuse angle (more than 90°, less than 180°)

Bigger than a right angle but not yet straight, like a laptop opened wider than a square corner.

Straight angle (180°)

A half turn. The two rays now point in opposite directions and make one straight line.

Today we name each angle the orange ray makes. As I drag the ray slowly, everyone calls out together: acute, right, obtuse, or straight.