6 – Measurement of Physical Quantities
Q 1 Who is my companion?
Answer
(1) Velocity - metre/second
(2)
Area - square metre
(3)
Volume - litre
(4)
Mass - kilogram
(5)
Density – kilogram cubic metre
Q. 2.
Explain giving examples:
(1)
Scalar quantity : Scalar quantity is completely expressed by its magnitude
alone e.g., length, breadth, area, mass, temperature, density, time, work, etc.
In scalar quantity only magnitude, i.e. a value with a unit, is used to express
it.
(2)
Vector quantity : Vector quantity is expressed completely only when megnitude
and direction are both given, e.g.
(1)
(i) The displacement of 20 kilometres to the North and (ii) Displacement of 20 kilometres
to the East is different from each other. Here the distance is same but the direction
of the displacement is different from each other.
(2) (i)
The aeroplane travelling at the speed of 500 km/hour to the North and another aeroplane
travelling 500 km /hour to the East are different from each other. Here speed
is the same but in (ii) the direction of velocity is different.
Q. 3.
Write answers to the following questions in your own words:
(1)
Why is the weight of the same object different on different planets?
Ans.
The gravitational force that acts on this mass is called its weight. When any
object on the earth is pulled by the gravitational force, it gets attracted to
the centre of the earth.This is called its weight on the earth. But on different
planets the gravitational force may be of different magnitude. Therefore, the
weight of the same object will be different on different planets
(2)
What precautions will you take to make accurate measurements in day-to-day
affairs?
Ans
(1) Proper instruments should be used while taking any measurement (2) These
instruments should be used by proper and scientific procedure. (3) We must check
that the things which we buy have been weighed properly by standardized weights
and balance.(4) The shopkeepers and the hawkers use balances. We must confirm
that these balances
carry
the stamp of standardization (5) The balance should be stable. With its pointer
in upright position (6) The underside of the balance should be checked for any
tampering done (7) The weights used should be of proper metals
(3) What is the difference between mass and
weight?
1. The
amount of matter present in
1. The gravitational force that acts on this substance is called mass: mass is called its
weight.
Mass
is a scalar quantity. 2. Weight
is a vector quantity
3.
Mass remains the same everywhere.
3. Weight may differ in different places
and in different conditions.
(4) Explain, giving examples, the errors that
occur while making measurements.
Ans. The major causes of errors in the
measurement are as follows:
1. Not using the appropriate device at the
time of measurement: (1) The hawkers and shop-keepers may not use standardized
weights at the time of business. They may use stone pieces or some other
matter. This results in inaccuracy of measurements. (2) The balance may not be
working properly. (3) Sometimes while buying petrol or diesel, the indicators
on the machines may not work properly.
2. Not
using the deice properly : (1) In daily life we come across many equipments of
measurements such as weighing balance, spring balance, ruler, measuring tape,
different weight of specific value. Measuring vessels for milk etc. (2) While
weighing on balance, the jerk given causes pointer to fluctuate and give
improper reading. (3) While measuring the cloth from the bundle, the shop
keeper may not measure the cloth with accuracy. Customers should pay keen
attention to the measurements while buying things.
(5) Explain the need for accurate measurement
and the devices to be used for that.
Ans.
The need for accurate measurement is dependent on the following factors:
(1)
The measurement of anything should be absolutely accurate in our daily life. If
measurements are not done properly, it may have long-lasting bad effects. (2)
Measurement of precious substances is extremely important. Also the substances
used in very small quantities have to be measured meticulously and accurately,
e.g. precious metals of gold and silver should be accurately measured. (3)
Proper instruments are now available due to advancement in science and technology.
Devices that measure very small magnitudes of quantities like distance, mass,
time and temperature, are now available These devices and instruments should be
used with precision. (4) Digital thermometers are not used for the measurement
of body temperature accurately. (5) The sports competitions like Olympics need
extremely accurate clocks for measuring distances and time.
(6)
How is 'second' standardised?
Ans.
(1) The time required for one revolution of the earth is measured by means of
an accurate device. (2) This time is taken as 24 hours. (3) This is then
standardized (4) One hour is considered to have 60 minutes and one minute to
have 60 seconds. (5) By appropriate methods the item period of 1 second is then
standardized.
Q. 4.
Give reasons :
(1) It
is not proper to measure quantities by using body parts as units.
Ans.
The measurement of body parts for every person will be different. There is no
standardization of any kind. Therefore, it is not proper to measure quantities
by using body parts.
(2) It
is necessary to get the weights and measures standardized at regular intervals.
Ans.
Due to constant use, the weights and the weighing apparatus may lose their
standardization. Using such devices may result into mal practice. Therefore, it
is necessary to get the weights and measures standardized at regular intervals.
