# ProtractorHTML5

## Summary

This animation illustrates how to use a protractor to measure an angle.

Click and drag the protractor and its blue handles to make some measurements.

A plan angle defines the space on the plan delimited by two crossing lines. The intersection of the lines is the tip of the angle.

The tool used to measure angles is the protractor. The most popular version is the half disc split into 180 equal parts that each correspond to one degree. The protractor is graduated from 0 to 180 degrees (°). Another form of protractors available would be the full disc graduated from 0 to 360°. To facilitate its usage, the protractor often possesses two graduations going in both directions.

The most common units of measures for angles are the degree (°) and the radian (rad).

Handling the protractor:

• Position the origin of the protractor on the tip of the angle to measure.
• Align the 0° graduation of the protractor with one of the side of the angle.
• Read the graduation that follows the second side of the angle

Click and drag the protractor and its blue handles to make some measurements.

## Learning goals

• To teach how to place a protractor in order to properly measure an angle.
• To be able to establish the measure of an angle by using its complementary (example of the javelin and of the inclined road).