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# 4. Gravitation

#### Mass & Weight

Mass Weight
1. Mass of a body is defined as the quantity of matter contained in it. Weight of a body is the force with which it is attracted towards the centre of the earth.
W = mg
2. Mass of a body  remains constant and does not change from place to place. Weight of a body changes from place to place. It depends upon the value of g. Weight of a body on another planet will be different.
3. Mass is measured by a pan balance. Weight is measured by a spring balance.
4. Unit of mass is kg. Unit of weight is newton or kg-wt.
5. Mass of a body cannot be zero. Weight of a body can be zero.
Ex. astronauts experience weightlessness in
spaceships.
6. Mass is a scalar quantity. Weight is a vector quantity.

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#### NTSE Physics (Class X)

• Electricity
• Magnetic Effect of Curent
• Light Reflection
• Light Refraction
• Human Eye & Colourful World
• Source of Energy
• Motion

#### NTSE Physics (Class IX)

• Force & laws of motion
• Work and Energy
• Gravitation
• Sound

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