Angles – ‘Right’ and ‘Straight’
In Geography, we have dealt with the concept of directions. We know that China is to the north of India, Sri Lanka is to the south.
Or let's just take a simpler example: We know that the Sun rises in the East and sets in the West. There are
They are North (N), South (S), East (E) and West (W). Now,
Say, we have an aerial view of a man walking on an open field. If we have to direct him to start walking "North" with respective to his position, in which direction does he need to walk? Draw the line segment joining the position of the man with the appropriate point.__
Now, which direction is opposite to North ?
Say, the man has returned to his original position. He is instructed to start walking towards the "right direction"? Draw the appropriate line segment to depict this. This direction is the
Which direction is opposite to East ?
We see that all the four directions have an angle equal to
Let's continue the directions.
We can use our knowledge about directions to understand a few properties about angles.
Do this: Stand facing north. Turn clockwise to East. When you do that, we say, "You have turned through a right angle".
Follow this again, by a ‘right-angle-turn’, clockwise.
Now, you would be facing South.
If you turn by a right angle in the anti-clockwise direction, which direction will you face? It is
From facing north to facing south, you have turned by
Isn't this the same as a single turn by two right angles?
The turn from north to east is by a
The turn from north to south is by
Stand facing the South direction. Now, turn by a straight angle. Which direction do you face now? You face
To turn from north to south, you took a straight angle turn, again to turn from south to north, you took another straight angle turn in the same direction. Thus, by turning
Now think, how many right angles should you turn in the same direction to reach your original position?
Turning by two straight angles or
Such revolutions can be seen on a clock. When the hand of a clock moves from one position to another, it turns through an angle.
Let see the Angles clock.
Angles made by a clock
As seen below, when the hand of a clock moves from one position to another, it turns through an angle. Suppose the hand of a clock starts at 12 and goes round until it reaches at 12 again. Has it made one revolution?
If we observe the "hands of the clock" for say, an hour, the following cases arise:
The minute hand often makes right or straight angle with the hour hand. When a hand of the clock has completed one revolution, how many right angles has it moved?
In most of the cases, the angles aren't "right angle to each other" or directly opposite to each other. What can we do about these other cases?
In the below given clock, try to move any one of the clock hand of your choice and observe the angle being made by the hands.
Note that there is no special name for three-fourth of a revolution.