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PRESSURE
Pressure
All matter is made up of tiny molecules
The force they exert over an area determines pressure
Measured:
US: psi:
pounds per square inch
Metric: Pa: Pascals
How is pressure determined?
Pressure = Force / Area
All fluids (liquids, and gases) exert pressure.
Where is pressure evident in our lives?
Why do we feel pressure
Earths atmosphere: Held in by gravity
-Pulls gases toward center of earth
Closer to Earth surface – more breathable air, more pressure
Why do our ears “pop”?
-to equalize the pressure of our bodies (inside vs. outside)
Increase Altitude
Less breathable air = Less Pressure (Less fluid friction)
Less Air to heat=colder temperatures
Fluids: Pressure varies with depth
Water-denser than air
Exerts more pressure per sq. inch
Deeper=colder (less sunlight)
What are “the bends?”
Rapidly changing pressure causes the
gases in the body to get dissolved
– bubbles form in the blood stream
(like bubbles in soda)
Boyle’s Law
Pressure, volume inversely related
One variable goes upThe other goes down
Ex: squeeze a balloon
(decrease volume, increase pressure)
Brakes on a car
Decrease volume - Increase pressure
Fluids (Air) move from areas of
high pressure to low pressure
Increase volume (lungs expand) Decrease volume (lungs contract)
Decrease pressure
Increase pressure
-air rushes in
-CO2 expelled
Fronts / Pressure
Cold Fronts
•Drops Temperatures ~15oF
•Generally moves from the N and W (for NJ)
Low Pressure
Pulls in moisture from all around it.
Clouds are “squeezed”
http://hint.fm/wind/index.html
Fronts / Pressure
Warm Fronts
•Raises Temperatures ~15oF
•Generally moves from the W and S (for NJ)
High Pressure
Pushes clouds away - clear skies
Cold air is more dense
and it sinks beneath the
warmer air and forces it
upward.
Warm air is less dense
than cold. It moves in
and is uplifted by the
cooler air. It condenses
and forms clouds
Barometer – Measures Air Pressure
Lower Pressure = Cloudy/Precip.
Higher Pressure = Fair Skies
Mb = millibars (Metric: ex-980 mb)
In = inches (US: ex 29.7 in)
Anemometer – Measures Wind Speed
•Wind is caused by air flowing from high
pressure to low pressure
•The closer the high and low pressure areas are together,
the stronger the winds.
Buoyancy
Buoyancy
Buoyant Force
-Upward force that a fluid exerts on all objects
Displacement
-the moving aside of matter to make room for
something else.
Archimedes Principle
-If an object floats, it must have displaced
a volume of fluid that weighs more than
itself.
Density = Mass
Volume
Mass – (g) grams
Volume – (mL) – for liquids
(cc) – for solids
Density – g/mL or g/cc
Steel: Density 7.8g/cc
Water: Density 1.0g/cc
Spread out over an area
Compacted
Even though this ship is large, and made of steel, its overall density is less than the
water. The steel is only about 3-4 inches thick. The hull is filled with air which
makes the ship less dense than the water
Also keep in mind that some of the ship sits
below the water level
Bernoulli’s Principle
Pressure in a moving stream of fluid has
less pressure than the surrounding fluid
“Faster moving air exerts lower pressure than slower moving
air”
Anatomy of a curveball
Air - Spin of ball = slower moving air
Air + Spin of ball = faster moving air
Soccer
Air + Spin of ball = faster moving air
Thus lower pressure
Air - Spin of ball = slower moving air
Thus higher pressure
Lower Pressure (from faster
moving air)
ANATOMY OF A CHIMNEY
Higher pressure (from
slower rising air)
Incorrect diagram in science textbooks. In the lefthand diagram above, the air
approaches the wing horizontally and also leaves the wing horizontally. This is
incorrect; it violates Newton's laws, since by F=ma there cannot be a lifting
force unless air is accelerated downwards. The wing must deflect the
horizontally-moving air downwards, as shown in the righthand diagram.
What’s the big deal? A little bit of ice forms on the plane and it weighs a
little more, I’m flying by myself, a little extra weight isn’t that bad is it?
Despite what most people think, the main danger ice presents is not
increased weight on the airframe, but what the ice does to the flow of air
around the aircraft. Ice (as well as frost and snow) change the aerodynamic
properties of airfoils (wings, control surfaces, even propellers) and disrupt the
smooth flow of air which increases drag and decreases the ability of the
aircraft to generate life. The added weight of the ice is insignificant compared
to the decrease in lift caused by the disruption in airflow. When power is
added and the nose is pulled up to counter-act the decrease in lift, it can allow
ice to form on the underside of the aircraft as well, decreasing lift further and
increasing the chance of a stall as the air becomes further disrupted. Even a
tiny amount can be dangerous:
Wind tunnel and flight tests have shown that frost, snow, and ice
accumulations (on the leading edge or upper surface of the wing) no thicker
or rougher than a piece of coarse sandpaper can reduce lift by 30 percent and
increase drag up to 40 percent.
http://www.grc.nasa.gov/WWW/k12/airplane/foil2b.html
http://phet.colorado.edu/en/simulation/buoy
ancy
http://www.yourdiscovery.com/everest/inter
active/effects.shtml
http://www.ricecookerstudios.com/assets/in
teractive/int004.swf
http://www.grc.nasa.gov/WWW/k12/airplane/atmosi.html
http://www.grc.nasa.gov/WWW/k12/airplane/foil2.html
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
http://www.grc.nasa.gov/WWW/k-12/airplane/bga.html
http://www.workman.com/more/games/fliersclub/