Question

Which one has more mass a bag of cotton balls or a bag of nails and explain

Answer 1

You would think that the bag of nails would have more mass but their masses are identical. If you were to put them both in a vacuum chamber and let them fall from a great height, they would fall the same speed. The vacuum chamber would suck all of the air out of the cotton balls, thus making it heavier and weigh the same as the bag of nails.

Hopefully this is helpful and makes sense.