Return to Mathematics IndexAn Introduction to Angles

Samuel A. Anoma Hyde Park Career Academy

6220 South Stony Island

Chicago, IL 60637

312-535-0880Objectives:

The students will be able to name, classify, identify and measure angles.Materials Needed:

1) Thin wooden sticks 10" x 1/2"

2) Protractors

3) Papers

4) PencilsRecommended Strategy:

1) Give each student three sticks, a protractor, a paper and a pencil. Let

each student put the paper on his or her desk. Then take one of the sticks and

put it on the paper horizontally. Take a second stick and join it to the first

stick vertically at the left endpoint. The two sticks join together to form

a pattern. The two sticks represent two rays having the same endpoint. The

stick put horizontally represents a ray going indefinitely to the right while

the stick joined to it vertically represents a ray going upward indefinitely.

The two rays with the same endpoint form anangle. The rays are the sides of

the angle. The common endpoint is the vertex of the angle. The angle formed

in this pattern is known as aright angle.

Protractors are used to measure angles. The units used in measuring

angles are degrees, minutes and seconds. In geometry, we usually use degrees;

in the above case,the degree measure of a right angle is 90.

2) Let the stick that is horizontal remain in the same position. Now rotate the

other stick clockwise. Another pattern is formed. Let the students draw it and

measure the angle formed.The sticks form an acute angle whose measure indegrees is greater than 0 and less than 90.

3) With the horizontal stick in the same position, rotate the second stick to

the left passing through the vertical position. Let the students draw the

pattern and measure the angle.The sticks form an obtuse angle whose measureis greater than 90 and less than 180 degrees.

4) With the horizontal stick still unmoved, rotate the second stick to the left

until it is in the same straight line with the horizontal stick. Let the

students draw the pattern formed and measure it.The sticks form a straightangle whose measure is 180 degrees.

5) Now that the two sticks are in the same straight line, let the first stick

remain in its position but move the other stick further in a counter-clockwise

direction towards the horizontal stick. This forms another pattern. Let the

students draw and measure it.This is a reflex angle whose measure is greaterthan 180 and less than 360 degrees.

6) Join the two sticks together in a straight line. Then join the third stick

to them at the endpoint where the two sticks meet. Let the students draw the

pattern and measure the angles formed.The three sticks form adjacent angleswhose sum is 180 degrees.Conclusion:

Discuss with the students the fact that angles are a part of their daily

lives. Streets and buildings are constructed using angles. Airplanes take off

on angles. Installation of revolving doors involve the use of angles. The

military bombers fire at angles. This experiment gives students a visual

appreciation of geometric vocabulary. They can experiment at home with pieces

of spaghetti. As homework, let the students classify the different angles in

their classroom and environment.