Pressure • What is pressure? Unit 5: Pressure Brent Royuk Sci-202 Concordia University Pressure Units Air Pressure • How can you tell the atmosphere is 1 N 1 lb pressurized? 1 Pa = 1 psi = 2 2 • What holds up the water? 1 m 1 in 1 psi = 6897 Pa € € The Atmosphere The Hydrostatic Paradox • What keeps the air from • The thickness of the column doesn’t matter, getting squashed to the only the height. ground? • Some light particles escape. • Why does the moon have no atmosphere? 1 Level Difference The Hydrostatic Paradox Application • Stevinus’s barrel demonstration • Water towers • Each foot of height provides 0.43 PSI (pounds per square Inch) • Bottle stream demo of pressure. A typical municipal water supply runs at between 50 and 100 PSI (major appliances require at least 20 to 30 PSI). The Barometer The Barometer • How high can the • How much does a 1 in2 column of water that is 34 ft column go? high weigh? • How much does a 1 in2 column of Hg that is 76 cm • Water: 34 ft high weigh? • Mercury: 76 cm • How much does a 1 in2 column of air that is 200 miles high weigh? • 1 atm = 14.7 psi =10.1 kPa = 76 torr • 1 bar = 10 kPa • Pressure bar • So why doesn’t all this pressure crush you to the floor? • So why doesn’t all this pressure crush your body? Pressure Underwater Pressure Underwater • SCUBA regulator delivers air at ambient pressure, • 27 ft below the surface tank: 3000 psi – http://www.mydivebook.com/modules.php?name=Forums&file=viewtopic&p=15 • Problem: Decompression sickness • Extreme form: Air embolism. 15 ft can be fatal. • Henry’s Law and soda bottles • Bubbles can form anywhere in body, producing various symptoms: – Joints- the “bends” – Brain- confusion, headache, tunnel vision – Lungs- the “chokes” – Skin- itching, rash • Nitrogen Narcosis- Rapture of the Deep – “Martini's law”: It's like one martini per 10 meters below 20 meters 2 Decompression Sickness Other Breathing Gases • Also known as Caisson Disease • Nitrox is a mixture of oxygen and air, and generally refers to mixtures which are more than 21% oxygen. It is mainly used instead of air to accelerate decompression or to decrease the risk of decompression sickness. • Trimix is a mixture of oxygen, nitrogen and helium and is often used at depth in technical diving and commercial diving instead of air to reduce nitrogen narcosis and to increase the maximum operating depth. • Heliox is a mixture of oxygen and helium and is often used in the deep phase of a commercial deep dive to eliminate nitrogen narcosis and to increase the maximum operating depth. Liquid Breathing Other Examples • Pressurized dissolved oxygen • How do we suck soda through a straw? • Mice and rats: 18 hours; dogs, 1 hour; – “Physics does not suck.” humans, anesthetized, 1 lung, 1 hour – Vacuum is nothing. Suction is the push of atmospheric pressure. • Problem: CO elimination 2 – You can’t pull a liquid. • The Abyss – Suction isn’t a pull- it’s a push. – I worked on The Abyss. At the time, I helped track down the last five gallons of medical-grade • How long could a straw be? perfluorocarbon at Duke University, which was • How do you inflate your lungs? purchased by the production for use in the scenes where the rat(s) breathe an oxygenated version of the • Snowshoes stuff. The rats survived quite nicely, though one developed a lingering cough that eventually cleared • Mouth vapor trick up. I owned a pet rat at the time and was concerned • How can you make a barometer that doesn’t that the rats used might develop chemical pneumonia if a lesser grade of PF was used, hence the effort to contain a liquid column? track down the medical grade PF. • What will damage a floor more, a stiletto heel or an elephant’s foot? Other Examples Free Diving • Which type of bike would be better to ride on sand, a AIDA recognized world records mountain bike or a racing bike? • Constant Weight, women: Sara Campbell, 96 m. • Why does a sharp knife cut better than a dull knife? • Constant Weight, men: Herbert Nitsch, 120 m. • Plungers • Constant Weight, women, without fins: Natalia Molchanova, 60 m. • Constant Weight, men, without fins: William Trubridge, 88 m. • Empty Me Fast! • Static Apnea, women: Natalia Molchanova, 8m0s. – Newton once worked in a plant that filled small-necked gallon jars with pop. One day a worker forgot to add • Static Apnea, men: Tom Sietas, 10m12s. flavoring and 500 gallon jars of pop were ruined. • Dynamic Apnea, women: Natalia Molchanova, 214 m. Someone had to empty all those gallon jars into a sink • Dynamic Apnea, men: Alexey Molchanova, 250 m. one by one. Naturally, they called on Newton to • Variable Weight, women: Tanya Streeter, 122 m. discover the fastest way to empty gallon jars. Using • Variable Weight, men: Carlos Coste, 140 m. Newton's method, they were able to empty each jar in • No limit, women: Tanya Streeter, 160 m. less than fifteen seconds. Can you find a fast method • No limit, men: Herbert Nitsch, 214 m. of emptying a gallon jar? 3 Aneroid Barometers Pumps • Rotary positive displacement pumps 4 .