LSS: GROUP 2 LENGTH & AREA.

Conversion of Area:

LENGTH

Length is a measure of distance between two points.

Length can be measured with many different units, the most common being:
a) Kilometre (Unit: km)
b) Metre (Unit: m) [SI unit for Length]
c) Centimetre (Unit: cm)
d) Millimetre (Unit: mm)

Conversions for the various units of length:

Most common instruments that are used to meaure length:

a) Measuring Tape

b) Metre Rule

c) External & Internal Calipers

d) Vernier Calipers

Measuring Tape

Accuracy: 0.1cm

Uses: Measures length of straight lines and curves, circumference of round objects.

A measuring tape can be used to measure lengths greater than 1m in length.
Measuring tapes come in different lengths - some can be as long as 60m.
There are two types of neasuring tapes, the ones used by tailors are soft and flexible while the ones used by contractors are stiff.
We can measure an object by having the zero mark at where you want to start and when you reached the object that you want to measure, that is the length of the object.
How to use a measuring tape?
1. Hold the front of the tape at the pointyou wish to start the measurement from, and extend it to the point you want to stop.
2. Read the first large number befroe your stop point
3. Read the smaller lines of various sizes and add the large number and the smaller number together.

Metre Rule

Accuracy: 0.1cm

Uses: Measures straight lines.

The metre rule is commonly used in the classroom or laboratory.

To measure the length of an object, simply place one end of the object against the zero mark and read off the mark rule at the other end of the object at the correct eye position.
When your eye is in the wrong positon for viewing,you may get what is called parallax error.

Vernier Calipers

Accuracy: 0.01cm

Uses: Measures external and internal diameters, depth of tube or hole.

Inside jaws- Used to measure the internal diameter of an object.
Outside jaws-Used to measure the extenal diameter or width of an object.

Main scale reading-The main scale gives measurements of up to one decimal place.
Vernier scale reading- The vernier scale gives measurements of up to two decimal places.
Tail extension- Used to measure the depth of an object or hole.

How to use the vernier caliper?

1.Close the jaws of the vernier calipers. Ensure that the zero marking on the vernier scale is in line with the zero marking on the main scale.

2. Place the object within the jaws of the vernier calipers and clamp it in place.

3.Read the length.

Zero Error

When the jaws of the vernier calipers are fully closed and the zero marking on the vernier scale does not coincide with the zero marking in the main scale, we have what is called a zero error.

> Positive zero error.

When the jaws of the vernier calipers are closed and the zero marking on the vernier scale fls on the rightnof the zero marking on the main scale, we have a positive zero error.

To determine the value of the positive zero error,close the jaws and look at the vernier to see which marks forms a straight line with a mark on the main scale.

For example,the third vernier mark coincides with a mark on the main scale. Hence ,the zero error is +0.03cm.

To find the correct reading, take the reading on the vernier scale and minus the zero error.

> Negative Zero Error

When the jaws of the vernier calipers are closed and the zero marking on the vernier scale falls on the left of the zero marking on the main scale, we would have a negative zero error.

Similarly, to determine the value of the negative zero error, close the jaws and look for the mark on the vernier scale that coincides with a mark on the main scale.

For example, the eighth vernier mark coincides. In this case, the zero error is two divisions from the tenth division. Hence, the zero error is -o.o2cm.

Area
Area is a measure of the size of a plane surface.

When we measure the space occupied by the surface of a figure, we are trying to find the area. The derived S.I unit for area is the square metre (m²).

Other commonly used units for area are square millimetre (mm²), square centimetre (cm²) and square kilometre (km²).

We can calculate the area of regular shapes by using the right formulae.

However, how can we measure the area of a irregular shape when it has no formula? We can estimate the area with the help of the grid paper.

Formulas: