In today’s post, we will learn what a straight angle is, how many degrees it has, and its properties. We will also practice with some examples.

Index

## What is a Straight Angle?

An angle is a portion of the plane between two rays that are joined by a vertex.

A **straight angle** is the shared space between two rays joined by a vertex measuring **180º**.

We can also think of an angle as the amplitude of a line’s rotation over a point. Therefore a straight angle has the amplitude of **180º **of a ray over a point.

## How Many Degrees Does a Straight Angle Have?

A straight angle measures **180 degrees** (180º). The amplitude of an angle can be measured with a protractor.

The most common protractors have an amplitude of 180º, in other words, a straight angle.

## How to Measure an Angle

To refresh your memory about how the amplitude of an angle is measured with a protractor, take a look at the following video of an interactive Smartick tutorial. It briefly explains the different types of angles, including a straight angle.

## When is an Angle Straight?

An angle is straight when the two rays that make up the angle are in the same position on opposite sides of a point. That is, they form the shape of a **line**.

A straight angle is when a ray makes a half rotation around a point. This way, it ends in the same position but pointing the opposite way. In other words, if you are standing looking at a door and turn 180º, the door will end up behind you. That’s why we say a person *‘has done a 180’* when they have completely changed their mind. For example, if one day a friend tells us that cats are their favorite animal and another day they don’t like them at all we can say that they have done a 180.

## Properties of Straight Angles

- Measures exactly 180º.
- Forms a line.
- A 180º turn always ends in the opposite direction.
- It is the boundary between convex (acute, right, and obtuse angles) and concave angles.
- It is the sum of two
*right angles.* - It is half of a complete angle.
- If we look at the angles within a circumference, it would separate the circle into two equal halves and correspond to the diameter of the circumference.
- When the sum of an
*acute angle*and an*obtuse angle*is equal to a straight angle, those angles are considered*supplementary*.

Additionally, in other blog posts, you can learn more about angles and the different types.

## Straight Angles Examples

We find examples of such angles frequently in our daily lives.

- You can find it when you read the hours on an analog clock. At what times do the clock hands form a straight angle?

- When you stretch your arms or a dancer stretches their legs you can see these kinds of angles.

- These are just some examples, can you think of more?

### Practice

Look at these Smartick exercises about this type of angle and think about how to solve them. You will find the solutions at the end of this section.

### Solutions

- Yes, it is. If you look closely the exercise itself is giving you examples of angles that are straight and those that are not.
- It is not a straight angle. The angle that appears is acute and convex.
- It is an angle that measures 180º.

If you would like access to real interactive exercises, register with Smartick, the online learning method for children ages 4 to 14 to learn math, and get started today!

Learn More:

- What is an Obtuse Angle?
- What Is an Angle? How Is It Made?
- Introduction to Angles: Definition, Parts, and Types
- The Relationship between Clocks and Angles
- Learn about Angles: Obtuse, Straight, Right and Acute Angle

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