Page 49 - Physics

Measurement

Measurement of mass Table 2.7: A comparison of the units of mass
Mass is among the fundamental physical Mass Comparison
quantities of measurement. It is defi ned with SI unit
as the quantity of matter in an object. It 1 tonne (t) 1 000 kg
measures the amount of matter in an object. 1 gramme (g) 1
The SI unit of mass is the kilogramme, 1 000 kg
abbreviated as kg. Other units of mass based 1 milligramme (mg)
1
on kilogramme are tonne (t), gramme (g) 1 000 000 kg
and milligramme (mg). Their equivalences
are as given below and in Table 2.7. Mass should not be confused with weight as
is evidenced in day-to-day discussions and
1 tonne = 1 000 kg. conversations. Weight is defi ned as a measure

1 kilogramme = 1 000 g. of the gravitational force acting on an object,
1 gramme = 1 000 mg. or is the measure of how heavy an object is.

Measurement of mass using different instruments
The equipment commonly used to measure mass of an objects in the laboratory include
a digital (electronic) balance, shown in Figure 2.21 (a), and a triple beam balance shown
in Figure 2.21 (b).

(a) Digital balance (b) Triple beam balance

Figure 2.21: Balances used to measure mass in the laboratory

A triple beam balance
A triple beam balance is used to measure the mass of an object. Its unit of measurement
is the gramme. It is called triple beam balance because it contains three beams, each with
specifi ed standard mass graduations or markings. The fi rst beam has 100 g graduations, the
second has 10 g graduations and the third beam has 1 g graduations with 0.1 g graduations
in between. To measure the mass of an object, the weights which are normally attached
to each beam, are moved along the beams.

How to use a triple beam balance

With the pan empty, move the three weights to the left of the beams, so that the balance
reads zero, shown in Figure 2.22. The balance pointer should be straight and aligned with

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