CBSE Class 6 Mathematics Understanding Elementary Shapes Chapter Notes

CBSE Class 6 Understanding Elementary Shapes Chapter Concepts. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

Understanding Elementary Shapes

Line Segment
A line segment is a part of a line that is bounded by two end points, and contains every point on the line between its end points. To compare any two line segments, we find a relation between their lengths. This can be done in several ways.
i) Comparison by observation
ii) Comparison by Tracing
iii) Comparison using Ruler and a Divider

Disadvantage of Comparison by observation
When two line segments of almost same length are to be compared, then by mere observation we cannot be certain about the line segment of greater length. Therefore, mere observation is not an proper method to compare lengths of line segments having slight difference between their lengths.

Advantage of Comparison using Ruler and a Divider
It is better to use a divider than a ruler in order to measure the length of a line segment because while using a ruler positioning mistake may happen due to inaccurate positioning of the eye.

Revolution
Turning by two straight angles (or four right angles) in the same direction makes a full turn. This one complete turn is called one revolution. The angle for one revolution is a complete angle.

We can see such revolutions on clock-faces. When the hand of a clock moves from one position to
another, it turns through an angle.

To Find the Angle between the Hands of a Clock
If “H” is the hours and “M” is the minutes then angle can be directly obtained by ANGLE = 30 H – (11/2) M
Example: When the time is 9. 30 the angle between the hands of the clock is

Measuring angle using Protractor
Angles are most commonly measured by degrees, but for those of you who are sticklers for accuracy, even smaller units of measure can be used: minutes and seconds. These kinds of minutes and seconds are like the ones on a clock — a minute is bigger than a second. So think of a degree like an hour, and you've got it down: One degree equals 60 minutes. One minute equals 60 seconds.

Before measuring an angle, spec it out and estimate which type you think it is. Is it a right angle? A straight angle? Acute or obtuse? After you estimate it, then measure the angle. Follow these steps:
1. Place the notch or center point of your protractor at the point where the sides of the angle meet (the vertex).
2. Place the protractor so that one of the lines of the angle you want to measure reads zero (that's actually 0°).

Using the zero line isn't necessary because you can measure an angle by getting the difference in the degree measures of one line to the other. It's easier, however, to measure the angle when one side of it is on the zero line. Having one line on the zero line allows you to read the measurement directly off
the protractor without having to do more maths.

3. Read the number off the protractor where the second side of the angle meets the protractor.

Some more advice:
· Make sure that your measure is close to your estimate. Doing so tells you whether you chose the proper scale. If you were expecting an acute angle measure but got a seriously obtuse measure, you need to rethink the scale you used. Try the other one.
· If the sides of your angle don't reach the scale of your protractor, extend them so that they do. Doing so increases the accuracy of your measure.
· Remember that the measure of an angle is always a positive number.

So what do you do if your angle doesn't quite fit on the protractor's scale? Look at Figure given below for an example. The angle in this figure has a measure of greater than 180°. Now what? Sorry, but in this case, you're going to have to expend a little extra energy. Yes, you have to do some math. These angles are known as reflex angles and they have a measure of greater than 180°.

Draw a line so that you have a straight line (see the extended dots on the Figure). The measure of this portion of the angle is 180° because it's a straight angle. Now measure the angle that is formed by the extension line you just made and the second side of the original angle you want to measure. Once you
have the measure of the second angle, add that number to 180. The result is the total number of degrees of the angle. In the above figure , 180° + 45° = 225°.
Perpendicular Lines
Perpendicular simply means 'at right angles'. A line is perpendicular to another if they meet at 90 degrees.

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