Topic 6 - Buoyancy

 Have you ever wondered how fish, octopus, squid, whales, etc manage to float completely submerged in water at different depths?  Why do some objects such as sailboats, icebergs, oil rigs, etc float partially submerged on the surface?

 Buoyancy is the tendency for materials to rise or float in a fluid  Also referred to as the buoyant force, it is the upward force exerted on objects submerged in fluids.  Without buoyant force, you would die, planes couldn’t fly and boats wouldn’t float.

The “Anti-Gravity” Force Floating occurs when an object does not fall in air or sink in water, but remains suspended in the fluid. The force of gravity pulls down towards the centre of the earth. The particles in the fluid exert a buoyant force in a direction opposite to that of the force of gravity.

 So, Gravity pulls down towards the centre of the earth And, Buoyancy pushes up and away from the earth Like all other forces, buoyant force is measured in Newtons (N)

 Why do you think some fluids can support certain objects?

 Is density the only factor that explains why certain fluids can support certain substances?

There are many cases where water supports objects that have greater density than water. Can you think of some examples?

There are many cases where water supports objects that have greater density than water. Can you think of some examples?  The Hibernia oil rig in Atlantic Canada

There are many cases where water supports objects that have greater density than water. Can you think of some examples?  The Hibernia oil rig in Atlantic Canada  Pretty much any boat, ship or tanker  Any others?

The reason that ships and tankers can float is because of their average density For example: The density of steel is 9.0 g/cm 3 The density of water is 1.0 g/mL Because of the large hollow hulls of ships, the average density is less than that of water.

The average density of the ship can be found by taking the total mass of all substances onboard the ship divided by the total volume of the ship The large hollow areas of the hull take up volume but have relatively little mass because of the air they are filled with. This keeps average density below that of water

The benefits of average density can be seen all over the place For example:  Fish and their swim bladders

The benefits of average density can be seen all over the place For example:  Submarines and other submersibles

The benefits of average density can be seen all over the place For example:  The Goodyear blimp or other airships

The benefits of average density can be seen all over the place For example: Also,  Hot-air balloons  Ocean-going ships