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MAZER
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The size of the buoyant force equals the
weight of the displaced fluid.
Think back to the method for measuring the volume of an object with
an irregular shape. This involves placing the object in a known volume
of a liquid, usually water. The level of the liquid rises. By measuring
the rise in the liquid level, you can figure out the volume of the submerged object. This method works because the object displaces some
of the liquid.
Archimedes’ Principle
More than 2000 years ago, a Greek scientist named Archimedes
was trying to understand forces that act on objects when they are
placed in water. He discovered that there was a connection between
the amount of water an object displaced when it was submerged
and the buoyant force. The buoyant force is equal to the weight of
the displaced water. This fact is often called Archimedes’ principle,
after its discoverer.
MAIN IDEA WEB
Use a main idea web to
take notes on
Archimedes’ principle.
Suppose you fill a beaker to the very top with water. What would
happen if you placed a marble into the beaker? Water would spill over
the edge of the beaker as the marble displaced the water in the beaker.
If you collected the spilled water in a container and weighed it, you
would know the buoyant force on the object.
The strength of the buoyant force acting on an object depends in
part on the fluid the object is placed into. You can see this easily with
Archimedes’ principle. Corn syrup is denser than water. If you dropped
a marble into a beaker of corn syrup, it would displace the same amount
of corn syrup as it would water. However, the displaced corn syrup
would weigh more than the same amount of displaced water. The
buoyant force due to corn syrup is greater than the buoyant force
due to water.
buoyant
force
(water)
buoyant
force
(corn syrup)
Chapter 4: Density and Buoyancy 119
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