Transcript Pressure
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/