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?

All fluids (liquids, and gases) exert pressure.

Pressure = Force / Area

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 up-The other goes down

Decrease volume - Increase pressure

Brakes on a car

Ex: squeeze a balloon(decrease volume, increase pressure)

Fluids (Air) move from areas of high pressure to low pressure

Increase volume (lungs expand)Decrease pressure-air rushes in

Decrease volume (lungs contract)Increase pressure-CO2 expelled

Fronts / PressureCold 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 / PressureWarm 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

Anemometer – Measures Wind Speed

•The closer the high and low pressure areas are together, the stronger the winds.

Barometer – Measures Air Pressure

•Wind is caused by air flowing from high pressure to low pressure

Lower Pressure = Cloudy/Precip.Higher Pressure = Fair Skies

Mb = millibars (Metric: ex-980 mb)

In = inches (US: ex 29.7 in)

Buoyancy

Buoyancy

Archimedes Principle

-If an object floats, it must have displaced a volume of fluid that weighs more than itself.

Buoyant Force

-Upward force that a fluid exerts on all objects

Displacement

-the moving aside of matter to make room for something else.

Density = Mass Volume

Mass – (g) grams

Volume – (mL) – for liquids

(cc) – for solids

Density – g/mL or g/cc

Steel: Density 7.8g/cc

Spread out over an area

Compacted

Water: Density 1.0g/cc

Also keep in mind that some of the ship sits below the water level

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

 

 

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”

Air + Spin of ball = faster moving air

Air - Spin of ball = slower moving air

Anatomy of a curveball

Air + Spin of ball = faster moving airThus lower pressure

Air - Spin of ball = slower moving airThus higher pressure

Soccer

Higher pressure (from slower rising air)

Lower Pressure (from faster moving air)

ANATOMY OF A CHIMNEY

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://phet.colorado.edu/en/simulation/buoyancy

http://www.yourdiscovery.com/everest/interactive/effects.shtml

http://www.ricecookerstudios.com/assets/interactive/int004.swf

http://www.grc.nasa.gov/WWW/k-12/airplane/atmosi.html

http://www.grc.nasa.gov/WWW/k-12/airplane/foil2.html

http://www.grc.nasa.gov/WWW/k-12/airplane/foil2b.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/