An Introduction to Angles
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Samuel A. Anoma Hyde Park Career Academy
6220 South Stony Island
Chicago, IL 60637
The students will be able to name, classify, identify and measure angles.
1) Thin wooden sticks 10" x 1/2"
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 an angle. 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 a right 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 in
degrees 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 measure
is 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 straight
angle 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 greater
than 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 angles
whose sum is 180 degrees.
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.