Q1.
What is the difference between weight and mass?
Answer
Mass is the amount of matter in an object. Weight is the gravitational force with which the Earth (or another planet) pulls that object. They are different quantities and are measured in different units.
| Mass | Weight | |
|---|---|---|
| What it is | The amount of matter in an object | The gravitational force with which the Earth pulls the object |
| Is it a force? | No | Yes — weight is a force |
| Unit | gram (g) or kilogram (kg) | newton (N) |
| Measured with | A beam balance (or the mass scale of a spring balance) | A spring balance |
| Does it change from place to place? | No — its value remains the same at every place | Yes — it can change, because the gravitational force varies |
The table the book gives makes the difference concrete. The same object is carried to different worlds:
| Earth | Moon | Mars | Venus | Jupiter | |
|---|---|---|---|---|---|
| Mass of the object | 1 kg | 1 kg | 1 kg | 1 kg | 1 kg |
| Weight of the object | 10 N | 1.6 N | 3.8 N | 9 N | 25.4 N |
Why it happens: the object still contains exactly the same matter wherever you take it, so its mass cannot change. Its weight is not a property of the object alone — it is the strength of the pull between the object and the world it is on. Change the world and you change the pull. Even on the Earth the gravitational force varies very slightly from place to place, so weight varies very slightly too.
Tip: in the market we say ‘the weight of this wheat bag is 10 kg’. Scientifically that is wrong on both counts — 10 kg is a mass, and weight would have to be given in newton. What we are really interested in when we buy wheat is the amount of matter, that is, the mass. Use the correct terms with their correct units, even when everyday language is casual.