Protractors and Angles
Lesson

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A protractor is a clear plastic device used to
measure angles from 0 to 180 degrees.  

protractor image

There are two sets of numbers on a protractor, so you can measure angles from either side of the protractor.

 

protractor image

Steps to using a protractor

1. Look at the angle you are measuring.
2.  If the angles are greater than 90 degrees (an obtuse angle) use the scale that is greater than 90.
3.  If the angles are less than 90 degrees (an acute angle) use the scale that is less than 90.
4.  Place the protractor on the angle so that the center point is on the vertex and the zero line is along one side of the angle.
5. Follow the scale beginning at zero and find the number where the other side of the angle intersects the scale on the protractor.
6.  The number where the line intersects is the degree of the angle.

 

Example One: Right Angle

Right Angles

A right angle measures actually 90 degrees.

protractor image measuring 90 degreesprotractor image measuring 90 degrees

 

Example Two: Obtuse Angle

Obtuse Angles

An obtuse angle measures greater than 90 degrees.

protractor image measuring 120 degreesprotractor image measuring 140 degrees

 

Example Three: Acute Angle

Acute Angles

An acute angle measures less than 90 degrees.

protractor image measuring 40 degreesprotractor image measuring 60 degrees

 

worm image

Remember:
A protractor is a clear plastic device used to measure angles from 0 to 180 degrees.


Let's Practice!

 
Topic Index| Grade 5 Math | Intermediate Test Prep | StudyZone

Created by Nicole Freebern 
Updated by:
  Julie Burger and Carrie Plasse
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