4.35. Archimedes’ Law http://www.ck12.org
4.35 Archimedes’ Law
- State Archimedes’ law.
- Explain how a heavy object such as a big ship can float in water.
Do you see the man sitting on top of this tanker truck? He gives you a sense of how big the truck is. What’s behind
the truck? Is it a huge apartment complex? It’s just as massive as a very large building, but it’s not even resting
on land. It’s a giant cruise ship, and it’s floating on water. The ship weighs about 100,000 metric tons. How can
such a tremendous weight float on water? Why doesn’t it sink to the bottom of the ocean instead? Archimedes’ law
explains why.
Archimedes Takes a Bath
Did you ever notice when you get into a bathtub of water that the level of the water rises? More than 2000 years ago,
a Greek mathematician named Archimedes noticed the same thing. He observed that both a body and the water in a
tub can’t occupy the same space at the same time. As a result, some of the water is displaced, or moved out of the
way. How much water is displaced? Archimedes determined that the volume of displaced water equals the volume
of the submerged object. So more water is displaced by a bigger body than a smaller one.
Q: If you jump into swimming pool, how much water does your body displace?
A: The water displaced by your body is equal to your body’s volume. Depending on your size, this volume might be
about 0.07 m^3.
Displacement and Buoyant Force
Objects such as ships may float in a fluid like water because of buoyant force. This is an upward force that a fluid
exerts on any object that is placed in it. Archimedes discovered that the buoyant force acting on an object equals the