This document discusses key concepts related to mass and weight in physics. It defines mass as the amount of matter in an object and kilograms as the SI unit of mass. Gravity is defined as the pull of the Earth and causes acceleration due to gravity (g), which is about 9.81 m/s^2. Weight is defined as the gravitational force on an object and is calculated using the formula w=mg. While mass is a fundamental quantity, weight depends on location and distance from Earth. A pan balance is used to compare standard masses to unknown masses.

1. Secondary or O-Level physics
~Dr Lalit kishore
The Plenum School, HP

2. Mass
 The amount of matter in an object is called mass
 Mass is a fundamental physical quantity besides
length, time, luminosity, temperature, electric
 SI unit of mass is kilogram
 The standard 1 kg mass is being kept at the
International Bureau of Standards in Paris which is
universally accepted for calibration all the National
Bureau of Standards or Standards Institutes in various
countries for calibration or marking of their mass
measures

3. Gravity
 The pull of the Earth is called gravity or
gravitational force
 Under free fall, gravity increases the velocity of the
dropped object in every successive time interval or
gravity as a downward force toward the earth
accelerates an object dropped from a height.
 The acceleration caused by gravity is called the
acceleration due to gravity denoted by ‘g’
 Galileo found that all bodies take the same time to
come to ground when dropped from same which
was verified by feather and coin experiment of free
fall in a vacuum tube

4. Weight as another name of
gravitational force
 The average value of g is 9.81 metres per second square
which is a constant value
 However, for fair approximation ‘g’ is taken as 10 metres per
second square which is a constant value
 The force caused by gravity on 1 kg mass is approximately
10 N
 Gravity/gravitational force is also called “weight”
 Gravity/gravitational force on 1 kg mass = 10 N
 Or, weight of 1 kg mass = 10 N
 Or, acceleration due to gravity = 10 N / kg or 10 m per second
square

5. Calculating weight
 The formula for calculating weight
In words
 Weight = Mass X acceleration due gravity
 Weight = Mass X gravitational force per unit mass
In symbols
 w = mg

6. Comparing mass and weight
Mass Weight
 Mass is quantity of matter in
an object– a fundamental
physical quantity
 Scalar
 Unit = kg
 Symbol = m
 Conserved
 Weight is gravitational force
of the earth on an object – a
derived physical quantity
 Vector
 Unit = N or kgf (1 kgf = 10 N)
 Symbol = mg
 Changes from place to place
and with distance from the
earth

7. Pan balance to compare standard mass with
a given mass for measurement
 The beam of pan balance is in equilibrium when mass
of the object and counter mass measures (put on the
right pan) are the same
 Pan balance is lever of first kind
 In labs the standard mass measures are kept in a
weight box
 Parts: Object pan, object arm, fulcrum, counter mass
pan, counter mass arm