Angles – protractor and midpoint
MathematicsPlane GeometryAges 11–12
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Plane Geometry
Two rays Ox and Oy pivot around vertex O to form angle xOy; a semicircular protractor lines up with ray Ox so you can read the measure. The simulation classifies the angle as acute, right, obtuse or straight from its measure, and draws segment AB joining a point on each ray together with its midpoint M, where MA = MB.
Lesson: Angles and angle measure; midpoint of a segment
What it shows
An angle is formed by two rays from a common vertex, and its size is measured in degrees with a protractor: the centre of the protractor sits on the vertex and its 0° mark lies along one ray, so the other ray points to the measure. Angles are classified by size: acute (less than 90°), right (exactly 90°), obtuse (between 90° and 180°) and straight (180°, with the two rays pointing in opposite directions). The simulation also joins a point A on one ray to a point B on the other and marks the midpoint M of segment AB, the point between A and B with MA = MB.
How to use
Set the Initial angle measure and the Drag snap step, then drag the end of ray Ox or Oy and have students read the measure on the protractor and name the type of angle. For estimation practice, hide the protractor with the Protractor button, ask for a guess, then show it again to check. Use the Midpoint button to display segment AB, then drag A or B and check that MA and MB stay equal.
Parameters you can change
- Initial angle measure 0–180 °
- Show protractor
- Show segment AB and midpoint M
- Drag snap step 1°, 5°, 10°
Questions to explore
- Why must the 0° mark of the protractor lie along one side of the angle?
- How are the two rays positioned in a right angle compared with a straight angle?
- As you drag A or B, does the midpoint M always stay between A and B? Why?
