Page 107 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

By dividing this height by the number of sheets, won't
we get the thickness of a sheet of paper?
Observe Fig.8.6 and find out how the thickness of a thin
metal wire can be found. Now try to measure the
thickness of similar objects.

Length of a curved line
Fig 8.5 Discuss how you can measure the length of the curved

line shown in Fig.8.7 using a thread and a metre scale.
Do you think you will be able to measure it by placing
the thread over the curved line? Try it. Note down the
Fig 8.6 length in the science diary.
Length of the curved line AB = .......... cm
B
Let's measure the diameter of a sphere
A
Fig 8.7
Have you ever thought of measuring the diameter of a
sphere?

Observe Figure 8.8 showing an object (for example a
ball) kept in between two wooden blocks, whose
diameter is to be measured. Measure the diameter of
the ball and write it down in the science diary.
Diameter of the ball = .......... cm

Fig 8.8

The basic unit of length is metre. Smaller units like centimetre (cm), millimetre (mm),
micrometre (micron - μm) nanometre (nm) are also used in certain situations for
convenience. We use a bigger unit like kilometre (km) to measure the distance
between two places. Units like astronomical unit (AU), light year (ly), paralytic
second known as parsec (pc) etc., are used for measuring distance to planets or
stars . One astronomical unit is the average distance from the earth to the sun. This
distance is approximately 15 crore kilometre. One light year is the distance travelled
by light in one year. In vacuum, light travels 3 lakh kilometre in one second. Parsec
is 3.26 light year.

Measurement Value in metre
3
1 km 1000 m = 10 m
1 cm 1/100 m = 1 2 m = m
10
1 mm 1/1000 m = = m

1 m 1/1000000 m = = m
1 nm 1/1000000000 m = = m

106 Basic Science VIII