Question

1 kilogram of cotton and 1 kilogram of iron are weighed in a vacuum then which one of them will be more.

Answer 1

"Which will weigh higher - 1 Kg Cotton or 1 Kg iron? "

Some will fall in trap (supposedly) and say that 1 kg iron weighs higher and then the questioner will smilingly say no, both will weigh the same as they are both 1 Kg.

Well if you go for a bit more accuracy and practical experience, it is not true!
1kg of cotton will weigh slightly less than 1kg Iron.

How???

I know it may sound baffling a bit. Here is the explanation.

1. Density of cotton is much less than iron.

2. Hence the total volume of 1 kg cotton will be much higher than 1 kg iron.
(See the pics)



3. So 1 Kg cotton will displace more air than 1 kg iron.

4. A larger buoyant force will act on cotton in relative to iron.
- Buoyant force being equal to the weight of the fluid being displaced.

5. Result will be slight decrease in weight.

So next time if a child asks you the same question - you can tell him both will weigh the same, but if questioned by a scientist or professor, you can show off a bit!

Note -
1. If you somehow wrap both the things and do the measurement inside water, the difference can be significant.
2. In vacuum both will weigh the same!