# Homework Help: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heavier

1. Sep 29, 2008

### lotusbio

I am not a student and this is not homework. I am just a thinking individual who would like to know the following:
Weight is a product of mass and gravitational force. If the mass of two objects like a ball of cotton and a ball of iron is the same (1 kg) and the gravity is the same because both are at the same place on earth, why does the iron feel much heavier than the cotton?

2. Sep 29, 2008

### Foxhound101

Re: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heav

Wouldn't it take a lot of cotton to equal 1 kg? And as far as I know, if they have the same mass, then they should have the same weight.

3. Sep 29, 2008

### mgb_phys

Re: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heav

They are exactly the same weight and feel just as heavy.
Try picking up a 50lb suitcase full of cotton clothes and decide if it feels light!

The only cicumstance where 50lb of cotton would feel lighter is if you droppe dit in air and the extra air resistance woul dmake it fall more slowly than the iron.

4. Sep 29, 2008

### pantaz

Re: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heav

The OP appears to be ignoring density. A given volume of iron will weigh more than the same volume of cotton.

5. Sep 30, 2008

### Staff: Mentor

Re: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heav

Because our senses are deceptive.

When you put a piece of iron on your hand your senses don't tell you much about the mass of the iron, they rather tell you what's the pressure exerted on the hand. As iron is much more dense its mass concentrates on smaller surface, thus the pressure is higher and iron feels heavier. However, if you put the same mass of iron and cotton in a bag with a string attached, and you will pull the string to lift the bag, you will feel they both weight the same - that's because contact surface of the mass with your hand will be identical.

6. Jun 7, 2009

### Unit

Re: If the mass of 1 kg of cotton and 1 kg of iron is the same , why is the iron heav

what a great explanation, Borek!