1. Density and Buoyancy

2. Density and Buoyancy
Buoyancy is the tendency to rise or float in water or air.
The upward force exerted on objects submerged in fluids is called buoyant force.
The buoyancy of a fluid is related to a fluid’s density- the amount of mass in a certain unit volume of a substance.

3. Buoyancy: The Anti-Gravity Force
Which is easier…
Lifting something submerged in a pool? Or lifting something outside of water?

4. Buoyancy: The Anti-Gravity Force
Buoyancy refers to the ability of a fluid to support an object floating in or on the fluid.
The particles of a fluid exert a force in a direction opposite to the force of gravity. The force of gravity pulls down toward the center of Earth.
Buoyant force- the upward force on objects submerged in or floating on fluids pushes up, away from Earth.

5. Buoyancy: The Anti-Gravity Force
Floating occurs when an object does not fall in air or sink in water, but remains suspended in the fluid.
People can’t walk on water, but many of us can swim in water, and we can float on the surface of water.

6. Buoyancy: The Anti-Gravity Force
How can people travel in the air and on water if the density of their bodies is greater than the density of both these fluids?
It seems that water can support objects that have densities greater than water-as long as the weight of the object is spread over a large enough area.

7. The Hibernia oil rig has a mass of over 14 000 tonnes, but it floats on the water.

8. Average Density
Ships can be built of steel (density of 9g/cm3) as long as they have large, hollow hulls.
A large, hollow hull ensures that the average density of the ship (that is, the total mass of all substances on board divided by the total volume) is less than that of water.

9. Average Density
Similarly, life jackets are filled with a substance of very low density. Thus, life jackets lower a person’s overall density, allowing the person to float.

10. Benefits of Average Density
The Goodyear blimp is one of the largest airships in the world.
It can carry people as well as the substances that make up its structure.
This giant airship is filled with helium gas, the second lightest gas that exists.

11. Benefits of Average Density
An airship such as a blimp can float because its mass is relatively small compared to its enormous volume.
Therefore, its average density is slightly less than the density of the air surrounding it.