Mathematics
Term 1 Week 8 Angles
Strategy
Students can:
name different angle types
construct a protractor
measure an angle using a protractor
Activities to support the strategy
Activity 1 – types of angles
1. Provide the definition:
A right angle is an internal angle which is equal to 90 degrees.
Angles can be measured using a protractor.
Using an example, point out the right angle and tell students that this square tells you that the type of angle is a right angle and the number tells you the angle size (90). Angles are measured in degrees (°). So a right angle is 90°. All the angles below are right angles.
Show students that a right angle can be in any orientation or rotation as long as the internal angle is 90°.
Make up a range of cards showing examples and non-examples of a right angle. Have students respond to each card by saying right angle or not a right angle.
Remember to start with non-examples that are quite different from a right angle and move to non-examples that are close to a right angle. Students could make a right angle tester from card to check.
Students shape parts of their body to make different types of angles, e.g
use your hand/legs to make angles that are:
a right angle
smaller than a right angle
larger than a right angle
The teacher provides a copy of this picture of a body. Students draw the arms and legs on their picture to show different types of angles.
Draw a right angle on the left arm.
Draw an angle smaller than a right angle for the right arm.
Draw an angle larger than a right angle for the left leg.
Draw a right angle for the right leg.
Ask students to find real life objects at home which have angles such as: tools, pliers, clamps, can openers, tongs, crushers, nut openers.
Identify the parts of an angle - the arms and the vertex.
2. Introduce the names for the other types of angles - acute, obtuse, reflex, straight, revolution.
Students identify and record the different types of angles found in the environment. They describe the angles they have classified, e.g. All these angles are acute because (answer). Draw each type of angle and label the arms and the vertex, or list examples in a chart.
Students could match these descriptions to the correct label by colour coding or by playing matching games with a partner.
Activity 2 – using a protractor
1. Students look for pictures of or collect different types of protractors.
Discuss and list the features of a protractor, e.g. they all have a baseline, a centre marked on the baseline, a scale beginning at 0°.
Most protractors have two scales, one on the inside of the curve and one on the outside of the curve. Each scale goes from 0° to 180°.
Students discuss how to construct a protractor using a semi-circle of cardboard without using another protractor, for example, which angles could be immediately marked on the semi-circle?
Brainstorm strategies for accurately determining where 90°, 45°, 60° and 30° would be located, e.g. folding the cardboard to find 90°, then folding again for 45°. Ask students:
Can you locate 60° and 30° by folding?
Which angles would need to be estimated to locate on the cardboard?
In pairs, students construct and compare their protractors.
Use the constructed protractors to measure and record angles within the room. Students could also measure objects where the angles can change, such as scissors or a folded card.
Students compare their construction with a real protractor.
2. Students practise measuring angles using a protractor by following these steps:
Place the protractor over the angle to be measured.
Move the protractor so the centre of the baseline is on top of the vertex of the angle.
Make sure the baseline is on top of one arm of the angle.
Hold the protractor carefully so it does not move.
Count forwards from 0° along the scale until you reach the other arm of the angle.
The number where this arm crosses the scale tells you the size of the angle in degrees.