Download Density and Buoyancy

Density and Buoyancy
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Gravity is the force that pulls you down.
What is the force that pulls you up?
Buoyant force
Buoyant force is the upward pull on an object submerged in or floating on a
liquid.
Buoyancy is the tendency to rise or float in a fluid.
Buoyancy is related to the amount of water an object displaces.
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What is density?
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We can describe density in terms of how many particles are crowded into a
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particular area.
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When the particles in a substance are crowded close together, the
substance is dense.
For example a brick is dense
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When there is empty space between the particles, the substance is not as
dense.
Example: cotton balls
We can find the mass of an object using a balance scale.
We can calculate the volume of regular shaped objects using mathematical
formulas.
V=LxWxH
The King’s Crown
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Who: Archimedes
Where: Greece
When: 212 B.C.E.
What: How to find the volume of the king’s crown.
How: While taking a bath!
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When Archimedes stepped into an almost full bathtub, water spilled out onto
the floor. The solution to the problem became obvious: a solid object can
displace water (move it out of the way). Archimedes reasoned that the
water that was displaced in the tub must have the same volume as his body.
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He concluded that he could find the volume of the crown by placing it in a
full container of water and measuring the water that spilled out.
Archimedes carried out the test and proved that the crown was not made of
solid gold. The goldsmith had cheated the king!
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Archimedes applied his idea to another property of fluids. He thought that
the displaced fluid was the secret to whether or not an object would float in
a fluid.
He observed that when he stepped into a bathtub he sank because the
amount of water he displaced weighed less than he did.
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However, he floated when he stepped onto a boat on the water. His
conclusion was that a larger volume of water was displaced and that water
weighed more than the combined weight of Archimedes and the boat.
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Neutral buoyancy
Happens when an object immersed in a fluid does not rise or sink
Happens when the force pulling down (gravity)
equals the force pushing up (buoyancy)