The latest supertankers can carry enormous quantities of oil and displace 500,000 tons as they move—and yet they float in water. Exactly how much can these ships carry and how do they float?

#### Amazing But True

A supertanker is like half a soda can—just much larger! How much oil can be carried in half a “can” that large? You’ll need to be able to calculate the volume of the tanker to find out, but the answer is a lot (around 450,000 tons)!

As the force of gravity weighs down the oil filling the ship’s tanks, the exterior of the supertanker is pushing water out of its way, exerting a force on the water. **Pressure** is the ratio of a force to the surface area over which the force is distributed. The pressure created by the exterior of the supertanker pushing against the water is countered by the pressure of the displaced water pushing back against the bottom of the boat. That force is called **buoyancy**, and it is what holds the boat up. Every square foot of the tanker’s bottom carries 1.9 tons of weight that the buoyancy balances.

We owe the discovery of buoyancy to the great Greek scientist Archimedes. The story goes that he made the discovery while in his bathtub!

See for yourself: http://www.youtube.com/watch?v=xniW3_afO-0

#### Explore More

Watch the following time-lapse video to see a supertanker be built in 76 seconds!