Why will a dime and penny hit the floor at the same time?

Question

It's for a science project for my son whose in the fifth grade. I need the scientific answer when he preform this for his class.

Answer 1

the mass/weight of the two coins are about the same so the gravity exerted on each  is the same therefore they fall at the same speed.

Answer 2

Yes. See Newton's laws of motion.

Answer 3

Only in a vacuum. Otherwise surface tension and air resistance will alter the fall.

Answer 4

Yes, gravitational acceleration is a constant named "g"

g is equal to 9.8m/s^2 or 32.2ft/s^2 and everything on earth that falls will accelerate at this rate regardless of weight.  

Technically they do not because of air resistance and other small effects.  For example, it will take a feather longer to fall than a book.  However, if you put the feather behind the book and drop them together, they will fall at the same rate because the feather is feeling very little air resistance.  

I think you can neglect these non-idealities since it is for a fifth grade science project!!!