# Mass and Weight

## •    The amount of matter contained in a body is mass. •    The S.I. unit of mass is kilogram and is denoted by kg. •    The smaller unit of mass is gram and is denoted by letter small g. •    The mass of a body is measured by a beam balance. •    The weight of body is the force with which it is attracted towards the earth that is the weight of a body is the force of gravity on it. •    For a body of mass of m kg, the weight of the body, W = mg. The weight of a body at a given place depends on its mass. •    The weight of a body is not constant on the surface of the earth rather it is changing from place to place. This is due to the fact that shape of the earth is not perfect spherical, but an oblate spheroid. Thus, the value of acceleration due to gravity changes from place to place. •    SI unit of the weight is Newton and is denoted by capital letter N. •    One newton is nearly the force of attraction on a mass of 0.1 kilogram or 100 grams. •    The other unit of weight is kilogram force where 1 kg f is approximately equals to 10 N. •    The weight of a body is measured by a spring balance. It is expressed by stating both the magnitude and direction.•    Weight of a body always directs towards the center of the earth. •    The mass of a body remains constant everywhere on the surface of the earth or on any other celestial body. But the weight of the body changes from place to place due to the fact that it depends on the force of attraction of earth or other celestial body.

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• Q1

Why a person in a falling elevator feels weightlessness?

Marks:2

In a falling elevator, a person feel weightlessness because both the elevator and person are accelerating downwards at exactly at the same rate and no force is acting between the floor of the elevator and him.

• Q2

Define the SI unit of weight.

Marks:1

The SI unit of weight is Newton, which is defined as the force of earth’s gravity with which it pulls a body of mass 0.1 kg towards it.

• Q3

Where will a body weigh more- at the poles or at the equator?

Marks:2

The earth is not a perfect sphere, it is slightly flatter at the poles and bulging at equator that is it is an oblate spheroid..A body weighs more at the poles than at the equator as the acceleration due to gravity is maximum at the poles on the earth.

• Q4

How can the mass and weight of an object be measured?

Marks:2

A beam balance measures the mass of an object and a spring balance can be used to measure its weight.