Lesson Planning of PROTRACTOR AND ITS USE
Students` Learning Outcomes
- Recognize the standard unit for measuring angles as one degree (1°) which is defined as 1/360 of a complete revolution.
- Measure angles using protractor where:
- Upper scale of protractor reads the measure of angles from left to right.
- Lower scale of protractor reads the measure of angles from right to left.
Information for Teachers
- Upper scale of protractor and lower scale of protractor is depending upon the rotation of angle, as;
- The amount of turn from one arm of the angle to the other is said to be the size of an angle.
- The size of an angle is measured in degrees; and the symbol used to represent degree is “0”. There are 360° in a full turn (or circle).
- A protractor (D) is used to measure angles. In this section, we will learn the use of a protractor (D) that has the shape of a semi-circle and two scales marked from 0° to 180°.
- The two scales make it easy for us to measure angles facing different ways.
- To measure the size of angle ∠ABC, place the protractor.
- We use the inner scale to measure the angle ∠ABC, as the arm passes through the zero of the inner scale.
- Following the inner scale around the protractor, we find that the other arm passes through the inner scale at 60°. So, the size of angle ∠ABC is 60 degrees. We write this as follows;
- To measure the size of angle ∠PQR, place the protractor over the angle so that the Center of the protractor is directly over the angle`s vertex, Q; and the base line of the protractor is along the arm QP, of the angle.
- We use the outer scale to measure the angle ∠PQR, as the arm ray passes through the zero of the outer scale. Following the outer scale around the protractor, we find that the other arm, QR, passes through the outer scale at 120°. So, the size of angle ∠PQR is 120 degrees. We write this as follows:
- Some students may have trouble in handling a protractor. Let them carry on through the steps: be sure to read the measure from the correct scale. On a double scale protractor, an angle that looks to be less than 90°, the number less than 90° will be the measure. Conversely if the angle looks larger, students should read the greater number on the protractor.
- During this lesson teacher should consult textbook wherein and whenever it is applicable.
Material / Resources
Writing board, chalk/marker, duster, geometry box, textbook
- Say: “Today we will measure angles using a protractor.” Before asking them to take out your protractor, explain that a protractor is an instrument of measurement much like a ruler which measures centimetres in a straight line. While a protractor with which we measures and constructs angles. Show the wooden protractor.
- Say: “Let`s name and label the parts of a protractor”.
- Ask them to take out their protractor.
- Say, “let`s see what is on this protractor like D”.
- Ask following questions:
- How many edges does the protractor have? (Expected answer would be as; two)
- What is the shape of these edges? (Expected answer would be as; one straight and other circular)
- What is the number in middle that has a mark? (Expected answer would be as; 90 in middle)
- How many marks on circular edge?(Expected answer would be as; 180)
- Is it taking a half-circle? (Expected answer would be as; yes)
- If I have two half-circles, will it make one whole circle? (Expected answer would be as; yes)
- If 180 marks are in half-circle (one protractor), how many in whole circle (two protractors)? Let them think and reply 360.Then introduce that: there are 360 in one whole circles.
- What do these marks indicate? (Expected answer would be as; degree)
- Let them draw the D-shape with protractor on rough sheets.
- We use protractor.
- To measure given angles,
- To construct the angle of known measurement,
- To draw semi-circle,
- Each mark on protractor is called a Degree and one mark is (1/360) of the whole circle.
- Read the degrees from the side where zero and one arm coincides. If vertex is on left of the base line (Anti-clock wise) we will read from right. If vertex is on right side read from left.
- Ask the students: as;
- How should the protractor be placed while measuring an angle? (Expected answer would be as; The protractor should be placed on the ray in such a way that the end point of the ray is coinciding the center point of the protractor and arrow mark is in front of ‘0’ mark of the point).
- How are degrees counted? (Expected answer would be as; the counting of degrees is made from the direction of the ‘0’ mark)
- Where should the ‘zero’ mark of the protractor be?
- From where would be the measurement of the angle be read?
- Teacher should also involve students to solve exercise given at end of chapter of the textbook.
- Ask them to draw shapes from their own to practice the angle and a use of protractor.
- Assign activities from the textbook.