The building blocks of geometry. Read a little, then play. Clear all six games!
What it is
A point marks a position. A line goes on for ever both ways. A ray starts at a point and goes on for ever one way. A line segment has two end points.
Why it works
We show this with arrows and dots: an arrow means it goes on for ever, a dot means it stops here. So a line has arrows at both ends, a ray has one arrow, and a segment has two dots.
Why it matters
These are the building blocks of all of geometry. Every shape you meet is made from points, lines and segments.
A few examples
The edge of your ruler is like a line segment. A torch beam is like a ray. A dot on paper is a point.
What it is
An angle is made when two rays start from the same point. That point is the vertex, and the two rays are the arms.
Why it works
When we name an angle with three letters, like angle QPR, the middle letter is always the vertex, the point where the two arms meet.
Why it matters
Angles are everywhere: in clock hands, in an open door, and at the corner of every shape.
A few examples
In angle QPR, P is the vertex. The corner of this page is an angle. Open scissors make an angle at the joint.
What it is
Angles are named by how open they are: acute (small), right (a square corner), obtuse (wide), straight (a flat line) and reflex (bigger than a straight line).
Why it works
A right angle is a quarter turn. Anything smaller is acute; anything between a right angle and a straight line is obtuse; a straight angle is a half turn; bigger still is reflex.
Why it matters
Naming angles at a glance helps you draw, build and describe shapes quickly.
A few examples
A pizza slice is an acute angle. A book corner is a right angle. An open laptop is often obtuse.
What it is
We measure how open an angle is in degrees, written with a small circle like 90°. A full turn all the way round is 360°.
Why it works
The full turn is split into 360 equal parts called degrees, and we read an angle using a protractor placed at the vertex.
Why it matters
Degrees let us say exactly how big an angle is, not just small or wide.
A few examples
A right angle is 90°. A straight angle is 180°. A quarter of a full turn is 90°.
What it is
To compare two angles we see which one is more open. The more open angle is the bigger one.
Why it works
The size of an angle depends only on the turn between the arms, not on how long the arms are drawn. Long arms do not make a bigger angle.
Why it matters
This stops a very common mistake, thinking a wider or longer drawing means a bigger angle.
A few examples
A 30° angle with long arms is still smaller than a 100° angle with short arms.
What it is
Some angles have exact sizes: a right angle is 90°, a straight angle is 180°, and a complete turn is 360°. A reflex angle is more than 180°.
Why it works
Turning all the way round brings you back to the start, one complete angle of 360°. Half of that is a straight angle, and a quarter is a right angle.
Why it matters
Knowing these key numbers lets you check and describe any angle at a glance.
A few examples
Two right angles make a straight angle: 90 + 90 = 180. Four right angles make a full turn of 360°.
Have a go on paper first, then tap to see the clear steps.
Q1. A figure has arrows at both ends. What is it?
Q2. In angle QPR, which point is the vertex?
Q3. An angle measures 130°. What type is it?
Q4. Which is bigger, a 45° angle or a 120° angle?
Q5. How many degrees are in a complete turn?
Q6. Two right angles are joined together. What angle do they make?