AP Physics Mr. Jean September 20 th, 2011

The plan: Fluid Mechanics –Pressure –Atmospheric Pressure –Standard Pressure formula in fluids –Understanding pressure

Pressure Most basic pressure equation –Pressure = Force / Area –What exerts more pressure-per-square inch when walking a 100 lb woman in high heels or a 6,000 lb elephant?

–At the moment when only the heel rests on the ground. –Stiletto heels have an area of about 0.5cm 2. Elephants, unlike humans, walk with two feet on the ground at a time. Each foot is about 400cm 2. –Under normal conditions a woman’s heeled shoe can apply 20 times the pressure compared to an elephant’s foot.

Pressure 1 Pascal = 1N / m 2 1 Kilopascal = 1000N/m 2 1 atm =  10 5 Pa

Pressure Formula: Standard pressure equation P f = P i + ρgh P f = Final pressure reading (Pa) P i = Initial pressure reading (Pa) ρ = density of matter (kg/m 3 ) g = gravity (m/s 2 ) h = total height (m)

Demos Collapsing can  video Magdeburg hemispheres  video –von Guericke and the first vacuum pump, 1654 demo for Ferdinand III

Density Units? Density of water: –1000 kg/m 3 = 1 g/cm 3 “Specific gravity” Air, standard conds Wood (oak) 0.6 – 0.9 Liquid nitrogen 0.81 Ice 0.92 Water 1.00 Bricks 1.84 Aluminum 2.70 Steel 7.80 Silver10.50 Lead11.30 Gold19.30 Platinum21.40

Demos See Demo videos from AP folder.

For next day: –Buoyancy –The Bernoulli Effect –Archimedes’ Principle

The Bernoulli Effect When a constantly flowing fluid has regions of different speed in its flow, the pressure of the fluid will be lowest in regions where the speed is fastest. Why would the fluid change speed?  The “garden hose equation”  Terminology: “volume flow rate”

Archimedes’ Principle F Buoyant = B = m displaced fluid  g =  fluid V object g FBFB mg F B = “weight of the displaced fluid” Proof: imaginary plastic bag filled with water

Demos Bernoulli red fluid Floating ball Chimney effect Ball in funnel