7Is Diving Safe?SCUBA is safe, like motorcycling or sky-divingIf you understand the physics and physiology diving is safe
8Gas Laws and DivingEssential Question: “What conditions lead to perils facing divers including the bends and embolism?”
9How much does air weigh at sea level? Review!How much does air weigh at sea level?What is the weight of water at 33 feet (10 meters)?What is the pressure on a divers body at 33 feet underwater?Pressure increases linearly with depth (not exponentially). Pressure = psi (4 x 14.68) at 99 feet: 3 x for each 33 feet of water + 1 x for the 1 atmosphere of pressure from air pressure of the atmosphere.
10Around the BendsWhat are the bends?How is decompression sickness treated?
11Bends and embolismThe bends result when dissolved gases (mostly nitrogen) absorbed as air is breathed under pressure are released as gas back into the bloodstream.Embolism results when gases in the lung expand during ascent and rupture lung tissue, causing air bubbles to enter the bloodstream.These conditions can happen if a diver ascends too quickly.
12Boyle: volume and pressure Charles: temperature and volume Law MakersBoyle: volume and pressureCharles: temperature and volumeOutline basic concepts. Do not introduce equations at this stage.
13Cartesian Diver Activity Fill medicine dropper for neutral buoyancyFill soda bottle to just below topPlace dropper in soda bottleTighten bottle capSqueeze bottleNote observationsStudents should observe dropper descending when bottle is squeezed and ascending when squeezing is released.Boyle’s Law – When a gas is at constant temperature, there is an inverse relationship between the volume and pressure of the gas. As the volume decreases, pressure increases and as the volume increases, pressure decreases.
14Add small amount of water to soda can Place can on hot plate Pressure Can ActivityAdd small amount of water to soda canPlace can on hot plateWhen water in can boils remove canQuickly invert can and place in bowl of waterNote your observationsStudents will see the can rapidly collapse. As air in the can heats up, its pressure falls. When air cannot escape due to the can being inverted in water, the greater air pressure on the outside causes the can to collapse.Charles’ Law – When a gas is at constant pressure, there is a positive relationshipbetween the volume of a given mass of the gas increases and its temperature.As the temperature increases its volume increases and vice versa.
15The Gas Laws Essential Questions: What are the principles of Boyle’s Law and Charles’ Law?How is the ideal gas law used to calculate changes in volume, pressure and temperature when one or the other variables is held constant?Students will see the can rapidly collapse. As air in the can heats up, its pressure falls. When air cannot escape due to the can being inverted in water, the greater air pressure on the outside causes the can to collapse.
16The Equations Boyle’s Law: PV = k Charles’ Law: V1/T1 = V2/T2 Ideal Gas Law: PV = nRTn = number of moles of gasR = gas constant ( L·atm/mol·K)T = temperature in Kelvin
17Boyle’s Law: What does it look like? PressurePressureClick so that only the last line remains. This represents Boyle’s Law.VolumeVolume
18Charles’ Law: What does it look like? VolumeClick so that only the last line remains. This represents Charles’ Law.TemperatureTemperature
19Should divers care about the gas laws? Essential question: How do the gas laws relate to safe diving practices?
20Why should divers care about Boyle’s Law? Divers who know Boyle’s Law know if pressure decreases, volume increases.A diver breathes gases under pressure.If a diver ascends too quickly pressure goes down so gases dissolved in the bloodstream increase in volume.Remember what happens when you shake a soda can? Yup. Gases start to fizz in the diver’s bloodstream. Not good.
21Why should divers care about Charles’ Law? Air in a scuba tank is pressurized to about 3000 psi.What happens if the tank is heated, for example in a car on a summer’s day? Yup. The tank could explode. Not good.If a diver is close to a bends or embolism situation and is hypothermic, what could happen if the diver is quickly warmed up?
26Graph of Dive Table Data Bottom time at 70 feet (21.3 m)
27Misinterpreting Dive Computers Dive computers help divers avoid risky situationsAlgorithms use depth and time data to estimate the likelihood of decompression sicknessWhat happens if a diver cannot use the dive computer properly?
28How Does Volume Decrease With Depth? Assume a pressure increase of 1.0 atm for every 10 m of depth below the surfaceUse Boyle’s Law to calculate the volume of a gas at pressure every 10 m of depth to 100 mChart your data on graph paper
31Example ProblemIf a diver runs out of air at 15 meters underwater, and immediately ascends to the surface, what are the risks of an embolism?Assumptions:Constant temperatureLung capacity = 6 litersPressure increases 1.0 atmosphere for every 10.0 m of depth below the surface.
32SolutionLet P1, V1 and T1 = pressure, volume, and temperature respectively of the air in the diver’s lungs when the last underwater breath is taken.Let P2, V2 and T2 = pressure, volume, and temperature respectively of the air in the diver’s lungs at the surface.Since temperature is constant, use Boyle’s Law to calculate the increase in volume of the air in the diver’s lungs: P1 x V1=P2 x V2Rearranging, V2 = (P1 x V1)/P2P1 (pressure at depth) = 2.5 atmospheres, since = 15/10 x 1 = = 2.5 (Note that 1 is added for the 1 atmosphere of pressure at the surface.)V1 (initial breath underwater) = 6 LP2 (pressure at surface) = 1 atmTherefore, V2 = (2.5 x 6)/1 = 15 LThe volume of air is 15 liters at the surface. Since lung capacity is 6 liters, embolism is inevitable.
33Enriched Air (Nitrox)How might divers overcome the problem of absorbing nitrogen which then turns to bubbles if the ascent is too fast?Breathing pure oxygen under pressure carries a significant risk of oxygen toxicity.Divers use enriched air (nitrox) which has a higher percentage of oxygen than air, but with a lower risk of oxygen toxicity.
35Essential QuestionsWhat conditions lead to perils facing divers including the bends, embolism and oxygen toxicity?How do the gas laws relate to safe diving practices?What are the principles of Boyle’s Law and Charles’ Law?How is the ideal gas law used to calculate changes in volume, pressure and temperature when one or the other variables is held constant?