Properties of Fluids

How do ships float? The answer is buoyancy

Buoyancy The ability of a fluid, either gas or liquid, to exert an upward force on an object

Ships exert a force down onto the water (weight) If the force pushing back (buoyancy) is greater then the ship will float If the force pushing back is less, then the ship will sink.

Archimedes’ Principle Buoyancy is equal to the weight of the water displaced by an object If the weight of the water displaced is equal to the object then it will float If the weight of the water displaced is LESS than the weight of the object, then it will sink

Why does a wood block float and a steel block sink? The answer is Density

If they are the same size or volume, they displace the same volume and weight of water. The buoyant forces would be equal for both. The answer is in the masses of the block.

If the water, wood and steel have different masses but equal volumes, they must have different densities! The density of the steel is greater than the density of the water The density of the wood is less than the density of the water

An object will float if it’s density is less than the density of the fluid it is placed in.

If you formed the steel block into a hull and filled it with air… It would have the same mass, but a greater volume Density would decrease and the steel would float This is how ships float!

Balloon - The weight of the air displaced is equal to the upward force and if greater than the weight of the balloon the balloon will accelerate upwards. If the weight of the displaced air is less than the weight of the balloon the balloon will accelerate towards the ground. Submarine - Able to travel on the surface of the water or dive at will. Diving is accomplished by special ballast tanks with water, increasing the weight of the submarine. To rise the water is forced out of the tanks using compressed air.

Force exerted per unit area P=F/A Pressure Force exerted per unit area P=F/A

Pascal’s Principle A property of fluids (gases and liquids) that states: Pressure applied to a fluid is transmitted throughout the fluid

Hydraulic Lifts: a pipe filled with fluid connects a large and small cylinder. Pressure applied to the small cylinder is transferred through to the large cylinder

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

The more pressure exerted on a fluid the less velocity. Water will move faster through a narrower pipe than it will through a wider pipe because of pressure difference

Ex: Bernoulli’s principle The airplane wing is designed so that the top is curved and the bottom is flat. Taxiing down the runway, the air blowing over the top of the wing travels faster than the air blowing underneath. The faster air has a lower pressure, so the greater pressure on the bottom of the wing pushes the plane up. When it gets going fast enough this lifting pressure exceeds the downward gravitational force. The plane soars.

Resistance of a fluid to flow Viscosity Resistance of a fluid to flow

Low viscosity = flows easily High viscosity = flows slowly (resistant to flow) When a fluid begins to flow, the flowing particles transfer energy to the stationary particles. This causes them to flow, too.

If flowing particles do not effectively PULL other particles into motion then the viscosity is high If the flowing particles DO effectively pull the other particles into motion, then the viscosity is low.