FLUID MECHANICSPRESSURE, BUOYANCY, AND GAS LAWS

PROPERTIES OF FLUIDS

• CONTINUOUS

• AMORPHOUS

• FREE MOVING MOLECULES

• TAKE SHAPE OF CONTAINER

• LIQUID, GAS, OR PLASMA

ARCHIMEDES’ PRINCIPLE

The buoyant force on an object is equal to the weight of the fluid displaced.

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

CENTER OF BUOYANCY

The weight of a vessel acts downward over the entire structure.

CENTER OF BUOYANCY

it can be considered as acting on the center of gravity of the vessel.

Because the weight is distributed throughout the length…

CENTER OF BUOYANCY

The hull of a vessel is supported by water along its entire length.

CENTER OF BUOYANCY

The center of buoyancy exists underwater similar to the above-water center of gravity.

CENTER OF BUOYANCY

The relative positions of the center of gravity and the center of buoyancy will determine the stability of the vessel.

DENSITY

p = m/V

The density of water is 1 g/ml.

An irregularly shaped brass object (p = 8.5 g/ml) is immersed in water. What will its apparent weight be if its mass is 12 kg?

KINETIC THEORY OF MATTERMatter is composed of a large number of constantly moving particles.

Four Postulates:1. Large number of

molecules moving randomly

2. Molecules stay far apart on average

3. No weak bonds form4. Collisions are perfectly

elastic.

PRESSURE

Pressure = Force / Area

Units are Pa (Pascal) or N / m2

Pressure is exerted equally in all directions.

AIR PRESSURE

There are 101.325 kPa in 1 atmosphere

1 atm. = approximately 62 miles of air.

Hurricane Ivan had recorded pressure of 91 kPa.

PRESSURE UNDER WATER

If P = P0 + pgh, what will be the pressure exerted on a human body 30 m under water?

PASCAL’S PRINCIPLE

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

!"#"

= !%#%

BERNOULLI’S PRINCIPLE

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

QUIZ

• EXPLAIN THE DIVER USING ARCHIMEDES’ PRINCIPLE.

• EXPLAIN THE DIVER USING PASCAL’S PRINCIPLE.

CHARLES’S LAW

!"#"= !%#%

Is it realistic to hold pressure constant?

BOYLES’S LAW

!"#" = !%#%Is it reasonable to hold temperature constant?

GAY-LUSSAC’S LAW

!"#"= !%#%

Is it reasonable to hold volume constant?

COMBINED GAS LAW

!"#"$"

= !&#&$&

!# = '($

where n = number of molesR = gas constant 8.3145 J/mol K

for an ideal gas.