Forces in FluidsForces in Fluids

Chapter 13Chapter 13

Fluid PressureFluid Pressure

Section 13-1Section 13-1

PressurePressure

Pressure – the result of a force distributed Pressure – the result of a force distributed over an areaover an area

To calculate pressure, divide the force by To calculate pressure, divide the force by the area over which the force acts.the area over which the force acts.

Pressure = Force

Area

Pressure in FluidsPressure in Fluids

Water pressure increases as depth Water pressure increases as depth increases. increases.

The pressure in a fluid at any given depth The pressure in a fluid at any given depth is constant, and it is exerted equally in all is constant, and it is exerted equally in all directions.directions.

Air Pressure and the AtmosphereAir Pressure and the Atmosphere

Air pressure decreases as the altitude Air pressure decreases as the altitude increases.increases.

Forces & Pressure in FluidsForces & Pressure in Fluids

Section 13-2Section 13-2

Pascal’s PrinciplePascal’s Principle

A change in pressure at any point in a fluid A change in pressure at any point in a fluid is transmitted equally and unchanged in all is transmitted equally and unchanged in all directions throughout the fluid.directions throughout the fluid.

In a hydraulic lift system, an increased In a hydraulic lift system, an increased output force is produced because a output force is produced because a constant fluid pressure is exerted on the constant fluid pressure is exerted on the larger area of the output piston.larger area of the output piston.

Bernoulli’s PrincipleBernoulli’s Principle

As the speed of a fluid increases, the As the speed of a fluid increases, the pressure within the fluid decreases.pressure within the fluid decreases.

Lift – an upward force created by the Lift – an upward force created by the pressure difference between the top and pressure difference between the top and the bottom of an airplane wing.the bottom of an airplane wing.

BuoyancyBuoyancy

Section 13-3Section 13-3

Buoyancy – the ability of a fluid to exert an Buoyancy – the ability of a fluid to exert an upward force on an object placed in it.upward force on an object placed in it.

Buoyancy results in the apparent loss of Buoyancy results in the apparent loss of weight of an object in a fluid.weight of an object in a fluid.

Buoyant force – an upward force, which Buoyant force – an upward force, which acts in the opposite direction of gravity.acts in the opposite direction of gravity.

Archimedes’ PrincipleArchimedes’ Principle

Archimedes Principle – the force on an Archimedes Principle – the force on an object is equal to the weight of the fluid object is equal to the weight of the fluid displaced by the object.displaced by the object.

Density and BuoyancyDensity and Buoyancy

If an object is less dense than the fluid it is If an object is less dense than the fluid it is in, it will float. If the object is more dense in, it will float. If the object is more dense than the fluid it is in, it will sink.than the fluid it is in, it will sink.

When the buoyant force is equal to the When the buoyant force is equal to the weight, an object floats or is suspended. weight, an object floats or is suspended. When the buoyant force is less than the When the buoyant force is less than the weight, the object sinks.weight, the object sinks.