# Teaching Kids About Acute Angles

What is an acute angle?

The acute angle is small, less than 90˚ (degrees). It is one of many primary types of angles, along with a right angle (equal to 90˚), an obtuse angle (between 90˚ and 180˚), and a reflex angle, which measures more than 180˚ but less than 360˚.

You can remember the definition of an acute angle by thinking of this mnemonic: an acute angle is small.

What is an angle?

Firstly, what is an angle? We have to understand angles before we can start thinking about acute angles.

In geometry, an angle can be defined as the figure formed by two rays meeting at a common endpoint. The two rays — lines — that meet at the endpoint are called the ‘arms of the angle.’ An angle measures a turn, calculated in degrees or °. There are 360° in a complete turn. The endpoint is also known as the vertex.

You find out the size of an angle using a protractor, which is a bit like a ruler. It is a semicircular piece of flat, transparent plastic with lines marked on it. Then, you can line up the lines with an angle to measure the degrees of the angle.

What are the five types of angles?

A few different types of angles vary in size and measurement. Therefore, children need to learn about the other angles.

Acute angles are angles of measurement less than 90˚.

Obtuse angles are greater than 90° but less than 180°.

Reflex angles are greater than 180°.

Right angles are exactly 90˚ in measurement.

Straight angles are 180° exactly, so they are a straight line.

Complete angles are a whole angle, exactly 360˚ in measurement, and so are a circle.