14-May-15 Physics 1 (Garcia) SJSU Chapter 14 Gasses & Plasmas

14-May-15 Physics 1 (Garcia) SJSU Air Most common example of a gas is air, which is mixture of nitrogen and oxygen gas Density of water = 1 gram per cubic centimeter Density of air = gram per cubic centimeter = 1 kilogram per cubic meter Water is about 1000 times denser than air Weight of air is small but not negligible. For example, weight of air in this room is comparable to your weight (volume of room about 1000x your volume).

14-May-15 Physics 1 (Garcia) SJSU Atmosphere Density of air in the atmosphere decreases with increasing altitude. Most of atmosphere in the first 10 km (about 6 miles) of altitude. We live at the bottom of an ocean of fluid— the fluid is air & “ocean” is the atmosphere.

14-May-15 Physics 1 (Garcia) SJSU Atmospheric Pressure Atmospheric column of air Base: 1 square meter Height: 10 kilometers (10,000 m) Volume: 10,000 cubic meters Mass: 10,000 kilograms Weight: 100,000 Newtons (= 22,000 lb = 11 tons) Pressure: 100,000 Pascals (= 15 lb per sq. inch)

Demo: Air Heavier than Water Fill a glass with water to the brim then place an index card on top. Hold the card while you carefully invert the glass over a sink. If the seal stays tight, atmospheric pressure will support the weight of the water. 14-May-15 Physics 1 (Garcia) SJSU

14-May-15 Physics 1 (Garcia) SJSU Demo: Magdeburg Hemispheres Pair of hemispheres fit together with air-tight seal Most of the air is pumped out from the interior. Air pressure holds the two pieces tightly together. A A A A L A L - Atmospheric pressure - Low pressure

14-May-15 Physics 1 (Garcia) SJSU Check Yourself The surface area of a Magdeburg hemisphere is about 1/100 th of a square meter. If we evacuate the air from inside a pair, how large is the force holding them together (Atmospheric pressure is 100,000 Newtons per square meter)? What if only 90% of the air is removed?

14-May-15 Physics 1 (Garcia) SJSU Demo: Can Crush Pour small amount of water into an empty soda can. Heat water to boiling. Quickly transfer the can, upside-down, into a pan of cold water. Soda can is quickly crushed.

14-May-15 Physics 1 (Garcia) SJSU Can Crush, Analyzed Steam L A A Low Pressure Atmospheric Pressure Boil the water and inside of the can fills with steam, pushing out the air. Cool the can and steam condenses back into water, leaving almost a vacuum inside. Low pressure inside and atmospheric pressure outside.

14-May-15 Physics 1 (Garcia) SJSU Crush the Rail Tanker Car The interior of the tank car was washed out & cleaned with steam. Then all the outlet valves were shut and the tank car was sealed. All the workers went home for the evening and when they returned, this is what they found. Apparently as the tank car cooled, it collapsed. The shell on these tank cars is 7/16 th inch thick steel.

14-May-15 Physics 1 (Garcia) SJSU Demo: Drinking Straw L AA With lungs, you reduce pressure in your mouth and in the straw. The higher pressure on the outside pushes the liquid up the straw. Force due to the pressure difference must match or exceed the weight. Weight NO “SUCKING” FORCE

14-May-15 Physics 1 (Garcia) SJSU Prairie Dog Vacuum Prairie dogs captured by giant vacuum truck with a padded bin. L A Force

14-May-15 Physics 1 (Garcia) SJSU Boyle’s Law Density of a gas increases as it is compressed (volume decreased) As the density of a gas increases, the pressure in the gas also increases. Compress the gas by pushing in the syringe. Dial gauge shows increase in pressure. Syringe Gauge Tank

14-May-15 Physics 1 (Garcia) SJSU Breathing & Boyle’s Law L A A H

14-May-15 Physics 1 (Garcia) SJSU Demo: Stop the Funnel Water will not enter an air-tight container. H A Weight A A A Block exit hole

14-May-15 Physics 1 (Garcia) SJSU Buoyancy in Air Objects can float in air, just as they float in water, if the objects’ average density is less than the density of air. Hot Air Balloon Helium-filled Blimp

14-May-15 Physics 1 (Garcia) SJSU Zeppelins On May 6, 1937, the German zeppelin Hindenburg caught fire and was destroyed in less than one minute. Only 35 of the 97 people on board were killed. Most deaths did not arise from the fire, but were suffered by those who leapt from the burning ship. (The lighter-than- air fire burned overhead.) Those passengers who rode ship on its gentle descent to the ground escaped unharmed. Hindenburg was 10 times longer than today’s blimps

14-May-15 Physics 1 (Garcia) SJSU Demo: Neutral Buoyancy Balloon Tie a helium balloon to a long string and allow it to float upward until it can lift no more string. Cut the string where it touches the floor. Weight of balloon and string exactly balance the buoyant force.

14-May-15 Physics 1 (Garcia) SJSU Bernoulli’s Principle Where the speed of a fluid increases the pressure in the fluid decreases. This phenomenon is due to energy conservation; when fluid’s kinetic energy increases (velocity increases) its internal potential energy (pressure) decreases. A L Still Air Wind

14-May-15 Physics 1 (Garcia) SJSU Demo: Blow It Up Hold a sheet of paper in front of your mouth and blow; the paper will rise. L A

14-May-15 Physics 1 (Garcia) SJSU Check Yourself Wind blowing over the ocean causes waves to build due to Bernoulli’s principle. Where is the pressure lowered?

14-May-15 Physics 1 (Garcia) SJSU Blow the Roof If wind blows hard enough the low pressure above can create a large enough force to lift the roof off. New Orlean’s Superdome after hurricane Katrina L A

14-May-15 Physics 1 (Garcia) SJSU Demo: Blow It Off Bend cardboard into a U-shape. Place on table, legs down, and try to blow it off. Side view L A Front view Fast moving air in the channel between the card and the table creates a low pressure region, pressing the card downward.

14-May-15 Physics 1 (Garcia) SJSU Demo: Blow the Funnel Blow hard through a funnel with a ping pong ball in the funnel’s bowl. Ping Pong Ball BLOW

14-May-15 Physics 1 (Garcia) SJSU Airplane Wing Pressure difference created by Bernoulli effect creates upward lift. L A Wing LIFT FORCE

14-May-15 Physics 1 (Garcia) SJSU Demo: Throwing You a Curve Force on a spinning ball is perpendicular to the forward motion and towards the sided spinning with the flow of air around the ball. No Spin Forward Motion L L L H Bernoulli Spin

14-May-15 Physics 1 (Garcia) SJSU Demo: Keep It Up Objects in a moving steam of fluid are pulled to the center of the stream because pressure is lower inside the stream than outside. L A L A A A L L A A