(c) McGraw Hill Ryerson 2007

9.1 Fluids Under Pressure

• Fluids always move from high pressure to low pressure Fluids under pressure and compressed

gases are used for a variety of everyday tasks

See pages 314 - 316

Fluids Under Pressure

• Air molecules pulled by gravity = atmospheric pressure Air pressure increases as altitude decreases

The more air there is above, the more it compresses the air molecules below

Air pressure is lower at high altitudes When humans change altitude, our

bodies try to equalize the pressure differences by having our ears “pop”

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Pressure Differences

• Fluids will always attempt to move from high pressure to low pressure When we drink with a straw, we first remove

air from the closed straw, which lowers the pressure inside. The atmosphere, having a higher pressure, then tries to get into the straw, and pushes the fluid up and out of the way to try to get into the straw!

See page 316

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

This same idea is used for

many purposes, including

hydraulics, water rockets and

dental tools.

(c) McGraw Hill Ryerson 2007

Liquid Pressure and Buoyancy

• The pressure of fluids increases with depth When you dive deep, you can feel more pressure In Earth’s atmosphere and oceans, pressure also increases

with depth (air behaves like as fluid as well!)

Sea level is about the “deepest” the atmosphere gets• Sea level = 1 atmosphere = 101.3 kPa (kilopascals)• Top of Mount Everest = 1/3 atm = 330 kPa• From sea level, every 10 m in water depth = +1 atm• A submarine at a depth of 500 m has the equivalent

of a 500 000 kg object resting on every square metre!

See page 317

Liquid Pressure and Buoyancy

• Buoyancy refers to low density floating on high density The amount a fluid allows

objects to float = buoyant force

(c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

• Many vehicles, including submarines, airplanes and space shuttles all must consider pressure changes Submarine designers must

ensure the sub is safe design a way to change depths

When water is pumped in, density increases = sink

When water is pumped out,density decreases = rise Compressed air, kept onboard, pushes out water

Rising and Sinking

See page 318

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

(c) McGraw Hill Ryerson 2007

• Convection refers to the movement of low density over top of high density fluids

Rising and Sinking

See page 318

Take the Section 9.1 Quiz