# Cardboard Boat: Calculating Buoyant Forces

1. Dec 7, 2008

### chrozer

Ok so I'm in a Physics class and there is going to be a Cardboard Boat Race competition. So I have to build a boat out of cardboard for two people to fit in and it be able to float across a length's pool. I just want to know how you would find out if a boat that I build out of cardboard would float with 2 people in it. My teacher hasn't taught us anything about these kinds of physic concepts, but she said it has something to do about buoyant forces.

So my question is how do I determine if the boat will sink or not? Instructions on what I should do? Any ideas?

2. Dec 7, 2008

### mgb_phys

A boat floats when the weight of water it displaces is greater than the weight of the boat.
So you simply work out the volume of the boat below the water line (simpler if it is a simple shape!) multiply by the density of water (fresh water weighs 1000kg for each m^3)
Then add up the total weigth of the boat + the two people.

The simple way is to make a rectangular boat and calculate the area of the bottom, if you know the weight of the boat+people you can work out how much volume of water you need to displace and so work out how far up the sides the water will come - then you make the sides higher than that!

3. Dec 7, 2008

### chrozer

Any design ideas or tips?

4. Dec 7, 2008

### mgb_phys

Make it waterproof, avoid icebergs, wear lifejackets