 # Buoyancy, Density, and Water

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Buoyancy, Density, and Water

Properties of Fluids Overview: Archimedes’ Principle
Pascal’s Principle Bernoulli’s Principle Boyle’s Law

Density is the mass of a substance per unit volume (usually measured in grams per milliliters, g/ml). Buoyancy is the upward force that a fluid exerts on an object less dense than itself.

Q: How do ships float?

A: A greater force is pushing up on the ship than the weight force pushing down.
This supportive force is called buoyant force.

If the buoyant force is equal to the object’s weight, it will float.

If the buoyant force is less than the object’s weight, it will sink.

Bouyant force was explained by Archimedes and it became known as Archimedes’ Principle. Archimedes was a Greek mathematician who lived around the 3rd century B.C.

Archimedes’ Principle states that an objects weight will cause the object to sink while at the same time displacing the fluid.

If the weight of the water displaced becomes equal to weight of the object, it floats.

If the weight of the water displaced becomes less than the weight of the object, it sinks.

Q: Why is this principle important?

A: Properties of fluids ultimately determine the design of ships, airplanes, cars, and hydraulic machines.

Water exerts pressure in all direction.
Consider swimming in a pool. The deeper you go the more pressure you feel.

Pressure is a force exerted on an object per unit area.

As you know pressure is not exclusive to liquids
As you know pressure is not exclusive to liquids. The earth’s atmosphere exerts pressure all around you.

Pascal’s Principle Pascal was a French scientists who lived in the 1600’s. He discovered a property of fluids now known as Pascal’s Principle.

According to Pascal’s Principle pressure applied to a fluid is transmitted throughout the fluid.

For example when you squeeze a tube of toothpaste at one end, what happens?

Pressure is transmitted throughout the fluid toothpaste.
Why? Pressure is transmitted throughout the fluid toothpaste.

Calculating Forces Using Pascal’s Principle
Pressure = Force/Area = F/A In a system, P1 = P2:: F1 = F2 A1 A2

Pressure System

Bernoulli’s Principle
As the velocity of a fluid increases, the pressure exerted by the fluid decreases.

Bernoulli’s Principle

Boyle’s Law As a gas is squeezed into a smaller space, its particles will strike the walls more often, increasing its pressure. The opposite is also true.

Calculating Pressure Using Boyle’s Law
P1 V1 = P2 V2