Cotton or Iron ?

[Mark-b]

Here's a question:

which one is heavier :

1 kg of cotton or 1 kg of iron ?

this question was asked in my mid-term exam of physics

here's what I've answered, hope that's correct :

both have the same weights

but the weight of the 1 kg if iron to the gravity feels heavier than the 1 kg of cotton. For example: If you drop the two objects from a high building, the 1kg of iron will arrive to the ground before the 1kg of cotton

reason: because the cotton has a porous (permeable) skin, so the air can enter throught the pores and deaccelerate i'ts speed while the iron has a tight skin

[ninjamunky]

F = m*a (Newton's Second Law)

Weight is a force. Therefore, since they both have the same mass and acceleration of gravity is constant, they will have the same force toward the ground (downward) and the same normal force (the ground pushing back up, equal but opposite)

[Berserk87]

there both 1Kg...they both weight the same.

and both objects would fall at the same rate despite there difference in weight.

although the cotton could break up and float around a bit.

[MrA]

They both weigh the same and have the same mass. If you weight them, they'll both show the same on the scale, and neither will 'feel' heavier than the other. Dropped at the same time in a vacuum, they'll both land at the same time. In an atmosphere, which one lands first depends on how the materials are shaped. You can scrunch the cotton tightly install a ball and roll out the iron to be paper thin. If you drop them at the same time, the cotton will probably land first. Without more information, you can't determine anything about the behaviour in an atmosphere.

[-T- Member]

Dropped at the same time in a vacuum, they'll both land at the same time

Any two items dropped in a vacuum will land at the same time as gravity is removed therefore they fall at the same rate.

To the OP, 1kg of something is the same weight regardless what the object is, it's still 1kg

[spacer]

Any two items dropped in a vacuum will land at the same time as gravity is removed therefore they fall at the same rate.

To the OP, 1kg of something is the same weight regardless what the object is, it's still 1kg

It's the wind resistance, not gravity that is removed from the equation when talking about a vaccuum.

[Midge]

Any two items dropped in a vacuum will land at the same time as gravity is removed therefore they fall at the same rate.

To the OP, 1kg of something is the same weight regardless what the object is, it's still 1kg

air resistance is removed not gravity :p

[Sophism]

Any two items dropped in a vacuum will land at the same time as gravity is removed therefore they fall at the same rate.

To the OP, 1kg of something is the same weight regardless what the object is, it's still 1kg

Gravity is not removed, air resistance is removed as well as some other factors.

If you "removed" gravity then the objects would float and you would be the worlds richest man for inventing an anti gravity device ;)

[gregb0b]

I am surprised that your Physics teacher never demonstrated items in a vacuum tube. That's pretty standard stuff for even beginners physics.

[Jerbian]

Any two items dropped in a vacuum will land at the same time as gravity is removed therefore they fall at the same rate.

To the OP, 1kg of something is the same weight regardless what the object is, it's still 1kg

Gravity is not removed in a vacuum (air resistance is!) otherwise, the objects won't fall! Mra's answer is the best answer... Using the example of dropping objects from high buildings complicated the subject: you are adding to the subject of weight and gravity (the original question) another field of physics: fluid dynamics!

In short: the two objects have the same mass, the same weight (F= m*a, and that's why they fall at the same speed in vacuum tube, a huge one that is), but different volume (unless we squeeze the cotton) since iron has much higher density than cotton: m = density * volume.

Hope this helps.

[ninjamunky]

This is a conceptual question. There is no need to go into vacuums or air resistance, volume or shape. You are all over-thinking it. As I said in my original post, it's as simple as comparing them both with the equation F = m*a where m for each is 1kg and a is the gravitation constant for wherever you are.

[Hum]

I prefer to wear cotton, over iron. It's much more comfortable. :yes:

[DiEMOS]

^ what he said, but yea, they weight the same.

[StealMySoda]

As everyone has said. They both weight the same.

[Mark-b]

ok thnks :D

[Konstanov]

I prefer to wear cotton, over iron. It's much more comfortable. :yes:

I rather like my chastity belt.

[Growled Member]

Sounds like a trick question to me.