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Mass
- The amount of matter in a body
- It tells how much matter is present
- Its value is the same everywhere
- SI unit is the kilogram (kg)
- Measured with a balance
- has a fixed amount of matter
- mass stays the same anywhere
- measured in kilograms
- use a beam or physical balance
- compare with a known mass
- gives the object's mass
- Mass of an object is constant and can never be zero.
- Other units of mass include gram, milligram and quintal.
- Mass is measured by comparing with a known standard mass.
Weight
- The force pulling a body to Earth's centre
- It is the force of Earth's gravity on it
- SI unit is the newton (N)
- Its value can vary from place to place
- Measured with a spring balance
- Moon's gravity is weaker
- weight becomes one-sixth
- but mass stays the same
- hang an object on the hook
- the spring stretches
- the stretch shows the weight
- Weight depends on the mass and the acceleration due to gravity at a place.
- Weight varies with place and can be zero, while mass cannot be zero.
- The smallest value a spring balance can measure is found from its smallest division.
Hang each object one by one on the free end and watch the stretch.
- Less mass: small stretch.
- More mass: bigger stretch.
- Weight varies with mass.
Fill in the blank: ________ is the amount of matter present in a body.
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Explanation
- Mass tells how much matter is in a body and stays the same everywhere.
Fill in the blank: Weight of a body is measured using a ________.
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Explanation
- A spring balance measures weight from the stretch of its spring.
State whether true or false: An electroscope is used to measure the weight of an object.
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Explanation
- An electroscope detects electric charge, not weight; weight is measured by a spring balance.
Compare mass and weight.
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Explanation
- Mass is the amount of matter in a body; weight is the force with which it is attracted towards the Earth's centre.
- The SI unit of mass is kilogram (kg); the SI unit of weight is newton (N).
- Mass is constant; weight varies from place to place.
- Mass can never be zero; weight can be zero.
The weight of an object on the Moon becomes one-sixth of its weight on the Earth. What causes this change? Does the mass of the object also become one-sixth of its mass on the Earth? (NCERT Book Question)
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Explanation
- The Moon's gravitational force is one-sixth that of the Earth.
- Since weight depends on gravity, the weight on the Moon becomes one-sixth.
- Mass is the amount of matter and does not change with place, so the mass stays the same.
You go to the market to buy vegetables and fruits. Which physical quantity are you measuring — mass or weight? Explain your choice.
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Explanation
- When buying fruits or vegetables, it is the amount of matter — the mass — that we pay for.
- The quantity is measured in kilograms, which is the unit of mass.
- We loosely say "weight", but the actual physical quantity is mass.
The SI unit of mass is:
- (a) newton
- (b) kilogram
- (c) newton/kg
- (d) gram
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Explanation
- The SI unit of mass is the kilogram (kg).
The SI unit of weight is:
- (a) kilogram
- (b) newton
- (c) newton metre
- (d) kilometre
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Explanation
- Weight is a force, so its SI unit is the newton (N).
Weight of an object is measured by:
- (a) physical balance
- (b) measuring cylinder
- (c) spring balance
- (d) electronic balance
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Explanation
- A spring balance measures weight from the stretch of its spring.
If a person weighs 60 kg on Earth, what will be his weight on Moon?
- (a) 60 kg
- (b) 6 kg
- (c) 10 kg
- (d) 50 kg
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Explanation
- Weight on the Moon is one-sixth of that on Earth: 60 ÷ 6 = 10.
