Angle activity with online protractor

This activity allows manipulation and investigation of various types of angles. The online protractor tool can be used to practice measuring angles. It can be used at a variety of different grade levels. At its most basic for teaching about types of angles, acute, obtuse or reflex. For more advanced use to create angle problems in which the missing letter angle values have to be found. You can click and drag the handles to change the angles and the values will updated.

The controls

In all the modes individual angles can be shown or hidden for example click the angle (a). Notice when the value is hidden the angle value next to the angle arc is replaced by the corresponding letter.

The handles at the end of each line can be clicked and dragged to change the angle.

Mode 'one' Identifying angle types.

The initial mode is unique in that there is only one angle. This mode is great for identifying various types of angles. Click the angle type ctrl to either show or hide the type. So now you can change the angle by dragging a handle or clicking dice for a random value. The angle types definitions are listed in the glossary below.

Complementary Angles mode

In this mode a complementary angle is shown, complementary angles add up to 90° Initially the 90° is split by just one line but this can be changed by selecting a different number of lines. A standard school problem is to have one missing angle that needs to be calculated. You can produce infinite such problems by selecting calculate from angles display, now press dice for a new problem.

Supplementary Angles mode

Supplementary angles are angles that add up to 180°. This mode behaves exactly the same as the previous.

Angles at a point mode

The angles at a point add up to 360°. In this mode press = button to make all the angles equal. This can be good way to start a problem followed by small adjustments to the lines by dragging.

Angles at intersecting lines mode

The final mode deals with angles produced by an intersection of two lines. If you have selected calculate you will notice that only one angle is given and all the other 3 can be worked out using the vertically opposite rule, or spotting the supplementary angles.

Angles Glossary

Acute Angle
Any angle that is less than 90°
Right Angle
An angle that is 90°
Obtuse Angle
An angle greater than 90° but less than 180°
Straight Angle
An angle of 180° which makes a straight line
Reflex Angle
An angle greater than 180°

Related activities

The interactive clock angles activity can also be used in explaining angles.

Select the mode, each option is a different angle type.
Change this number to add or remove lines/angles to the current problem
Toggle to show/hide the type of angle currently displayed.
Click to set all the values to random values.
Click to automatically set angles so they are all equal.
Toggle the display of the protractor.
Select the paper background style
Press the random button and this is the initial display state for the angles