Answers to discussion topic questions in Unit 2

Please make sure you understand the answers before you attempt the practice quiz or unit test.  Many of these answers came from your fellow students.

Rotation

  1. Plasma and platelet donors have blood extracted and it is separated into its component parts by a centrifuge.  The target material is isolated and the remaining components are transferred back to the donor.  A centrifuge is a device that spins the blood in a circle.  Explain how this is accomplished considering that ALL the components of the blood are trying to "flee" the center in this device.

    It all comes down to density.  If you place water and oil in a container, the oil always moves to the top because of density (regardless of the amount or volume involved).  In a centrifuge, the same rule applies.  The liquid with the highest density will move farthest from the point of rotation.  Density is just mass per volume ... a measure of how compact the substance is.   BTW, red blood cells have a higher density than blood plasma.
     
  2. A mass spectrometer is used to identify the chemical composition of a substance.  In what way is this discussion on rotation pertinent to the way this machine functions?  What force provides the centripetal acceleration?  How is molecule "A" distinguished from molecule "B" if both ions have the same electric charge?

    The first step is to give the atoms a positive charge by stripping off electrons (which have almost no mass).  These positive ions are accelerated and then move through a magnetic field.  Charged particles are deflected in an external magnetic field because any moving charged particle produces a magnetic field of its own.  The two fields interact and the particle is deflected by magnetic pushes.  The amount of deflection depends on the speed of the particle (which is known), the charge of the particle, and the mass of the particle.  For simplicity, if we only consider ions with a +1 charge and all ions are given the same speed, the amount of deflection then only depends on the mass of the ion.  As an analogy, if cars are moving along the highway at 60 MPH and subject to collision from the side, the more massive trucks would deviate the least from their path and the lower mass passenger cars would show the most deflection.

     
  3. What provides the centripetal force when your car turns on an un-banked curve?  Why do speedways "bank" their curves?  Explain in terms of forces.

    If the road is flat, friction between the tire and road provide the necessary centripetal force.  However, you don't need any friction if the road is properly banked.  Using vectors, the image shows that when the road is banked, part of the cars weight is directed perpendicular to the road surface (shown in pink and called the "normal" force.  Since forces always act in pairs, the road pushes with an equal and opposite force on the car (arrow shown in green).  A component of this force is directed toward the center of the circle.  This is the centripetal force shown in red.  The steeper the bank, the greater this force becomes.  At any given speed, there is a "banking angle" that will provide 100% of the centripetal force.  That is, you could make the turn even if the road was glare ice.


     
  4. Perhaps conventional type rockets will no longer be needed to transport cargo into space.  Experts have proposed a space elevator could do the same job at a fraction of the cost.   Explain how that is possible and how it would work.

    Have you ever tied a rope to an object and swung it around your head?  Now imagine a spider crawling along the rope as it whirls in circles.  The key to the space elevator works a bit like this.  One end of the cable is attached to the earth's surface (at the equator) and a "weight" lies just beyond the geosynchronous orbit (the center of the mass of the entire system must lie at the geostationary point).   Tension is maintained in the cable as gravity from the earth pulls on the weight (centripetal force) and the weight pulls back on the earth (remember forces always act in pairs).  The payload climbs the cable until it reaches the desired height.  The problem is finding a super strong, lightweight cable.  Carbon nanotubes may be the answer but no one has perfected a large scale manufacturing process yet.
     

  5. Why do space rockets launched in the US fly toward the Atlantic Ocean rather than the Pacific Ocean?

    The space rocket must achieve a horizontal speed of about 18,000 mph to achieve orbit.  Why not let the earth provide some of that speed?  The earth rotates from west to east so a rocket resting on the launch pad already has some horizontal speed.  At the equator, this is about 1,000 mph.  That number becomes less as you move to higher latitudes.  However, any speed you already have at launch time is free if you move in the same direction that the earth rotates.  One student added that launching from Florida makes sense for two reasons - (1) flying over the ocean offers a safer path (we all know things can go wrong) and (2) the latitude of Florida is the closest we can get to the equator ... and thus, the highest west-east linear speed.  I'm guessing that launching from Hawaii would be cost prohibitive.
     

  6. Find an instance where the "ice skater effect" is observed or put to use.

    Did you ever notice that when someone is playing tether ball they tend to swing at the ball late after it has gone around the pole once or twice?  This is like the skater effect. The ball gets moving faster when the rope distance between the ball and the pole gets shorter. The player is anticipating a speed consistent with the last hit. The speed actually is greater due to the rope wrapping around the pole and this causes some players to miss the ball.

    Astronomers see examples of the "ice skater effect" often.  The classic example is seen in pulsars.  A pulsar is the collapsed core of a dead star but spins at incredible rates (thousands of revolutions per second).  Another example is seen in the earth-moon system.  Tides are slowly reducing the earth's rate of rotation (days are getting longer by .0023 seconds per century) due to friction.  To compensate, the moon moves further away from the earth (at 3.8 centimeters a year) to conserve angular momentum in the system.
     
  7. Give an example of positive feedback (not already covered in the eBook).

    Answers may very but the feedback must accelerate things to go even more off balance.  Example:  In a growing economy, the more money I make, the more I can invest, The more I invest, the more money I make.
     
  8. Give an example of negative feedback (not already covered in the eBook).

    Answers may very but the feedback must change things to bring balance in the system.  Example:  If the population of a species grows too big, there becomes less food available to feed the population.  The population drops due to starvation.

 

The Centrifuge

The centrifuge was first used to separate milk from cream.  It is now used and applied to:

Thermal Properties of Matter

  1. If a nut on a bolt (or jar lid) is difficult to move, should you apply heat or cold to help loosen it?  Hint:  You know what the bolt will do if it gets warmer or cooler.  What happens to the inside diameter of the nut if it gets hot?  Will it increase or decrease?

    Apply heat!  Everything expands .. including any tiny gaps that may exist between the nut and the bolt.  Note:  This effect can be accelerated if you heat the nut quickly (with a torch) .... and apply torque before heat is conducted to the bolt.  This way the inside diameter of the nut increases and the bolt's outside diameter is unchanged (making the gap even bigger).   
    animation

    Let's go one step further.  How about when opening a stubborn glass jar of pickles?  Glass and metal both expand when heated but metals expand more than glass when warmed to the same temperature.  This is similar to the thermal properties pointed out in the bi-metallic strips (in this section).  Because the metal expands more than the glass, the small gap between these surfaces widens.

    Note: I once worked at a facility that utilized the thermal properties of materials.  Before placing gears on shafts, the gear was heated and the shaft cooled so it would slide on easily.  The heat increased the inside diameter of the gear and the cold shrunk the outside diameter of the shaft.
     
  2. Is the thermostat in your car designed to prevent the car from becoming too hot or too cold?  What is the reasoning behind your answer?

    The common answer is that the thermostat is used to maintain a constant temperature of the engine.  I'll buy this answer.  However, what would happen if you had no thermostat at all?  Your car would run too cool because nothing would restrict the flow of coolant.  Some might ask ... wouldn't a cooler engine be better for wear and tear? Maybe, but you need a hotter engine to maximize your burning efficiency (plus your heater wouldn't work very well).  If you think of it that way, a thermostat is designed to prevent your engine from being too cool. After the thermostat opens (at about 190 degrees) it can do nothing should the temperature get even higher (water pump fails, etc).
     
     
  3. Rocks have been known to explode during a flash fire (I actually witnessed this once).  How is this possible?  Hint: Why do ice cubes crack when you drop them in room temperature water?

    Heat causes expansion.  When you drop an ice cube into a drink, it cracks because the outer layers of the cube suddenly heat up but the inner sections of the cube remain at the same temperature (it takes some time for heat to conduct to the center of the cube).  This produces internal stress within the ice ... enough to crack the ice.  You will find (in a later unit) how this phenomena can be put to good use.   However, another common answer to this question is also acceptable.  The rock may contain pores filled with water.  When the rock heats, the pressure of the trapped steam may be enough to blow the rock to pieces.
     
  4. Why is the bi-metallic circuit breaker shown in the material NOT used in most applications (such as your circuit board in your home)?

    One student wrote: The bi-metallic circuit breakers have some disadvantages. Because they are heat sensing devices they can be adversely affected by changes in surrounding temperature. When operating in a cold environment they will trip at a higher current level increasing the risk of damage of some appliances. When operating in a hot environment, they will trip in lower current levels resulting in unwanted equipment shut down.

    Another student wrote:  This type of circuit breaker (as shown) would shut off when the current heats up the bi-metallic strip. Once the strip cools a few seconds, and after it has opened, it will then close again and complete the circuit. Without some other mechanism keeping the circuit open once it is tripped, this would be a dangerous form of circuit breaker for your home.  This is, however, how many Christmas tree lights or the turn signals in your car are caused to blink.

    I added:

    Cool .. I'll buy this but I was really looking for the fact that the circuit has to first have dangerously high currents already flowing before it trips.   It all comes down to response time.  Things could be over heating (as well) down the wires before it trips.  You need a quicker way of sensing a dangerous overload and turning off the juice.  We cover a couple of ways in the next unit.  I like your answer though.
     

  5. You can tell when your Thanksgiving turkey is done with a small device known as a pop-up timer.  When it pops up, time to eat.  How does this device work and is it reusable?

    Inside this probe is a substance that melts at 185 degrees Fahrenheit to let you know the turkey is done.  The "pop up" section of this device is embedded (frozen) in this substance and once the correct temperature is reached, it is free to move.  A compressed spring delivers the energy to push the probe out.  To reuse it, just place the probe in boiling water (where the substance once again melts), and push the popup back in as it cools to room temperature.  This locks the popup back into the substance and re-compresses the spring as well.  All set for the next Thanksgiving feast.
     
  6. Why does metal always feel colder than wood, even though both are initially at the same room temperature?

    Metal is a good conductor of heat and wood is not.  The sensation of cold occurs when heat leaves your body.  In this case, heat easily escapes your body when you touch metal and not so much when you touch wood.  Thermal conductivity is important where you need to remove excess heat from an area.  The CPU of your computer generates a lot of heat.  Manufacturers apply a thin coat of thermal paste (goop that has a high thermal conductivity) to the back of the CPU to help move heat to nearby cooling fins (and then use a fan to blow it away .... that's convection).

     
  7. Suppose equal masses of dirt and water (at the same temperature) each absorb the same amount of heat.  Will both items reach the same final temperature?  Explain.

    On a warm sunny summer day in Milwaukee, the weather person will report "cooler near the lake".  There is a reason for this.   When equal masses of water and soil each absorb equal amounts of heat, the soil temperature will rise about five times higher than the water.  On a sunny summer Milwaukee day, the land will get very hot and the water temperature will only rise a little.  There is a big difference between the specific heat of soil vs. water.   Water has a high specific heat, which simply means it takes a lot more heat to get water hot.  Keep that in mind when you bite into hot pizza.  The hot cheese has a high specific heat, so a large quantity of heat is transferred to the roof of your mouth when the two surfaces meet.
     

Applications in Cryogenics - Cryogenics deals with the behavior of matter at very low temperatures.  Your mission is to post one important and/or practical application in the field of cryogenics.  You do NOT have to discuss how these low temperatures are achieved.

One practical application in cryogenics deals with the tempering (hardening) of metals.  In the past, heat was applied as a tempering agent, but it was found that tempering at low temperatures could work as well if not better.  Today everything from razor blades to brake rotors can be hardened at low temperatures.  In addition, cryogenics can be used to "un-warp" a piece of metal prior to machining it. The removal of heat puts the piece in its "most relaxed state". 

Low temperatures are frequently used in the medical field from freezing embryos to (killing) warts.

The space industry frequently uses liquid fuels (hydrogen)  in their rockets.  They even pack liquefied oxygen to provide an efficient burn.  All these require very low temperatures.

One interesting field in physics deals with superconductivity.  Certain materials show no electrical resistance at low temperatures.  Medical MRI imagers require a super strong magnetic field to work.  Some of these devices create this field by passing currents through superconducting wires (a huge electromagnet).

Cryogenic grinding. This is also known as cryomilling.   This process is cooling or chilling material and then reducing it into small particles. Basically it is for material that is hard to mill down at normal temperatures so it needs to be chilled by dry ice or liquid carbon dioxide to be able to be processed into fine powder.

OK, want to take cryomilling one step further?  Read this student post: Cryogenics is being used outside the US as an alternative to cremating a body.  The process is called promession.  The body is submerged into liquid nitrogen which makes it so brittle it shatters into powder as the result of slight vibrations.  This is supposedly a "green" way of disposing of a body by avoiding the release of pollutants into the air, and the remains degrade w/in 6-12 months after the procedure. It was invented and patented in 1999 by a Swedish biologist, Susanne Wiigh-Masak.  (The first facilities were scheduled to be ready in 2009 in Sweden, Germany, Great Britain, South Korea, and South Africa.)  www.en.wikipedia.org/wiki/promession

Hot Topics - Scientists have found ways of achieving very high temperatures ... not hundreds but thousands of degrees and much higher.    Your mission is to post one important and/or practical application when things get very hot. 

This topic is open ended.  You can only cool things down to absolute zero (about -460 Fahrenheit) but how high is high (when discussing temperature) is left to the imagination.  I suppose you could say the first and most important application of high temperature is fire.  Cooking comes to mind as an immediate application.  However, let's push the thermometer up a bit and see where it takes us.

Pressure

  1. If the atmospheric pressure is so high, why doesn't it crush in your skull?

    Your head does not contain a vacuum (I hope) so the pressure of the atmosphere is not acting against your skull unopposed.  The pressure inside your skull is at the same pressure as the outside.   It all has to do with pressure differences!    You will notice any slight changes in pressure as an irritating or painful discomfort in your ears.  For example, if you take an elevator up a tall building, you may notice the difference in your ears.  A yawn may equalize the pressure.  You feel this when driving in mountains or in airplanes.  Who can forget Arnold Schwarzenegger's response to a sudden drop in pressure in Total Recall?  Getting back to reality, divers experience great pressure increases over a very short distance.  If a diver goes just 34 feet down, he/she will experience twice the pressure compared to the surface.  The diver's lungs are compressed to half their volume.  Diving below 100 feet requires a slow ascent to the surface to avoid "the bends" .. where nitrogen (which is diffused into your bloodstream at that pressure) and needs to be released out of the blood slowly.
     
  2. A suction cup 6" in diameter is fastened to a wall.  If the inside of the cup holds a complete vacuum, how much force would you need to dislodge it?

    The area covered is πr2 or 3.14 x 32 = 28.26 in2  assuming a surface pressure of 14.7 pounds/ in2 we get 28.26 x 14.7 = 415 pound of force

    In 1654     Otto von Guericke (who invented the vacuum pump) performed an experiment to demonstrate the power of a vacuum.  Two steel hemispheres (about 20 inches in diameter) were sealed by a vacuum.  Even a team of horses could not pull the two sections apart.
     
  3. Will a soda straw work at any length?  Explain.

    No!  Look again at the way a mercury barometer works.  Imagine you were trying to drink some mercury from a straw (not a good idea).  If you were a perfect sucker (is one born every minute?),  you could only draw the mercury up about 30 inches because the atmosphere is pushing it up the tube.  Water is much less dense so a perfect vacuum would allow the atmosphere to push water about 34 feet.  You can bet that miners who needed to pump out water knew this.
     
  4. From a physics point of view, what factor(s) determines the liquid pressure at the bottom of a beer bong?

    There is only one factor - height of the liquid column.  For example, if the column were 34 feet high, the pressure would be equivalent to one atmosphere of pressure.  OK, if you want to get technical, you would have to take into consideration the density of the liquid but beer is basically water.  Also, you could argue the absolute pressure at the bottom of the bong should take into account the pressure of the atmosphere but I'm only concerned with the pressure difference due to the liquid.  My guess is that if you used one of these devices too many times it would become difficult to answer any of these questions  :)
     
  5. Will a depth gauge give different readings under fresh water vs. salt water?  Explain.  If different, which would tend to give the higher number?

    A depth gauge is really a water pressure gauge.  Salt water is slightly denser than fresh water.  As a result, at any given depth the gauge would read slightly higher in salt water.  The difference in readings is not a significant factor for divers ... but sharks are.   Note: Cargo boats have a "load line" (Plimsoll line) that indicates the safe level for loading.  If the boat is loaded in New Orleans at the mouth of the Mississippi River, and you load exactly to this line, the boat will rise up (above this line) once it sails away because the saltier (denser) ocean water offers more buoyancy.
     
  6. You are under buoyant force right now!  Explain.  Give an estimate how large this force is.

    The buoyant force is equal to the weight of the displaced fluid.  You are displacing air right now so you would need to estimate your volume and the weight of an equal volume of air.

    Estimate: What is the volume of the human body?  You can fill a huge barrel brim full of water, climb in and submerge yourself under water.  Now measure the volume of displaced water (amount that flows out).  I'll try a slightly easier approach.  I'll assume that the density of the human body is slightly greater than water.  Let's go 1.1 g/cm3.   A 150 pound person has a mass of 68 kg = 68,000 grams.  Since D= m/V :   V = m/D  (V = volume, m = mass, D = density)  V = 68,000 g / 1.1 g/cm3 = 62,000 cm3 .    Now the density of air is 1.2 kg/m3 from     here.  Convert this to .0012 g/cm3  Now m = DV  so .0012 x 62,000 = 74 grams

    Wow ... all that work to find that you are "lighter" by about 3 ounces due to the buoyancy of air.  Don't worry, you will NOT have to do a calculation like this on any test.
     
  7. A classic rock group called itself "Led Zeppelin".  Could a zeppelin constructed from lead actually fly?  Explain.

    Hey, steel is a whole lot denser than water yet steel boats float on water.  The key is to make sure your ship's total weight is equal to the weight of the displaced liquid (water).  Blimps only fly if the same rule applies but now you are displacing air.  A lead balloon was actually made on the show Mythbusters:  season 6 episode 2.   All you need is a lead chamber holding a low density gas (hydrogen or helium).  I'm thinking how gold (which is almost twice the density of lead) can be pounded into a very thin foil.  Imagine helium filled gold balloons by Donald Trump!  I'm not a materials engineer but I know that lead is also very malleable.  Anyone want to make a lead zeppelin?  If you do, maybe you will find a "stairway to heaven".

    One student commented that this makes the phrase "going over like a lead balloon" an invalid statement!
     
  8. Water may not be compressible, but air certainly is.  The density of air is considerably greater at the surface than it is at higher elevations.  How does this affect the buoyancy of a zeppelin with a rigid hull?  Is there a limit to how high it can go?

    Have you ever noticed that weather balloons are only partially inflated when leaving the ground?  This is because as the balloon rises in the atmosphere, it encounters less outside pressure and expands to create an equilibrium.  With a rigid hull (like the Goodyear blimp), the pressure within the chamber remains fairly constant (ignoring temperature changes).  It only has buoyancy as long as its total weight equals the weight of the displaced surrounding air.  However, the (fixed) volume of surrounding air weighs less and less the higher you ascend into the atmosphere.  It eventually reaches a maximum height and can go no higher.  In the case of a hot air balloon (which you can think of as having a fixed volume), you gain height by making the inside air hotter.  This makes it expand which forces air out of the balloon and makes the overall weight less.  The balloon rises until it moves into thinner air and a new equilibrium is established.  The air inside the balloon eventually cools and becomes denser.  This draws in surrounding air and adds weight to the system ... down you go.

     
  9. How are submarines able to surface and dive (from a standpoint of Archimedes' principle)?

    Submarines have ballast tanks that are filled with air or water.  To make the sub surface, compressed air is fed into the tanks and the overall weight and density of the U-boat drops.  Remember, the sub will float if the weight of the sub equals the weight of the displaced seawater.  To make the sub dive, the ballast tanks are flooded with water ... changing the overall weight and density of the boat.
     
  10. Describe how the common pressure gauge known as a Bourdon gauge works.

    You're likely to have a dial Bourdon pressure gauge attached to any pressure tank.  It works by the same principle as those "party snakes" you blow on and a coiled paper tube extends out to annoy the person sitting next to you.  The gauge contains a thin hollow coiled tube that tends to straighten itself when the pressure inside increases.  The change in the tube shape is transferred (via a linkage) to a dial reading.  The animation below should help you see how this works.

 

Bourdon Pressure Gauge animation
 

11.  One process, called pascalization, is used in the food industry.  Explain what is involved here.  Does it affect the taste of foods?  Does this process work on all foods?

Pascalization involves the use of extremely high pressure to kill harmful bacteria in foods.  The public has seemed to reject the use of irradiated food (despite frequent stories of contaminated food with deadly results).  Pascalization offers an alternate means for public safety.  It does not alter the taste of food but only works on certain foods like meat products but does not work in fruits and vegetables (turning them to mush).
 

12. Why is it essential to “bleed” air out of your car’s brake line?

The hydraulic fluid in your brake line is uncompressible .... meaning its volume does not change regardless of the pressure.   This is important because any pressure applied from the foot peddle (and vacuum assist) can be transferred equally (via the hydraulic fluid)  to the brake pads.  If there is a tiny air bubble in the system, your brakes will not work because air IS compressible.  This means the volume will change (lower) when outside pressure is applied.  The necessary transfer of pressure from one system to another is greatly reduced.  Crash!!!

 

Applications of a Vacuum (many answers from students)

Just about any spinning blade will create pressure differences.  The household vacuum cleaner creates positive pressure on the "bag side" and negative pressure on the floor side.  The same idea is seen in a shop vac, exhaust fan, blower fan in your furnace, etc

Toilets in airplanes flush by a vacuum.   During flight, the air pressure outside the craft is considerably lower than the passenger cabin.  All you need is to tap that pressure difference to move the waste materials to a holding tank ...  at least we hope there is a holding tank onboard   :)

Respirators use both positive and negative (vacuum) pressure to help patients breath.  The iron lung was one of the first applications.

Vacuum is used in the technique called freeze drying.  When the pressure drops below a certain point, water boils (even at or below room temperature).  This drives the water out of food without cooking it.

When we heat water at conditions where the pressure is lower than the atmospheric pressure, then the boiling temperature will be lower.  It works with other liquids too and can be used to separate one component within a liquid from another.  This is because the different substances have different boiling points.  This process is called vacuum distillation. This process is necessary when liquid substances need to be separated but they can be destroyed in high temperatures. The vacuum distillation is most commonly used in the oil refinery industry.

There is an entire industry devoted to making plastic things shiny!  The process is called Vacuum Metalizing and how it works is they literally melt metal until it evaporates into a cloud.  Then they use this "cloud" of metal in a vacuum chamber along with the item to be coated and because of the vacuum, the particles go straight to the object and go back to their solid state.  (Note from Jim:  Good!  However, the vacuum here is only used so the cooler target is the only item the vaporized metal can condensate on.  The vacuum itself doesn't exert any force on the "cloud" to go one way or the other.  This process is very similar to the way dew forms on grass in the morning)

Vacuums are used a lot in food packaging, for example, hot dogs.

A (partial) vacuum is established inside a CRT (cathode ray tube).  This is done to prevent particle collisions.  The idea is to direct a beam of electrons to the phosphor coating on the inside of the television tube.  Without a vacuum, most of the electrons would never reach the screen.

A vacuum is used to remove blood in a syringe.  There is even a vacuum established in a test tube known as a Vacutainer.  Look for this the next time you donate blood.

Small spider cracks in a windshield can sometimes be repaired by applying a vacuum to extract air in the cavity and allowing a resin to fill the void.

Vacuum leak testing is used to detect minute leaks in welds, gaskets, seals, valves, etc.  A certain gas or liquid on the high pressure side diffuses through the (possible) leak and is detected on the vacuum side with a sensor.

Auto body shops frequently use a vacuum to pop out dents and/or create a suction cup on an area to apply "pull points".

A thermos bottle uses a vacuum chamber to reduce the transfer of heat via conduction (and convection) between the inside bulb and the outside jacket.

In the manufacturing of a light bulb, a vacuum is use to extract the combustible oxygen from the bulb which is replaced by low pressure argon gas.  Argon is used because it is non-reactive and it helps reduce the "evaporation" of tungsten atoms off the filament.

The printing and bindery industry uses necessary vacuum systems for lifting envelopes and pages.

Lumber is treated by submerging a board in a bath of liquid preservative within a vacuum chamber.   Once the vacuum is released, the preservative is drawn deep into the wood.

NASA spent $23.4 million for a space station toilet that uses a vacuum to draw 850 liters of air per minute (along with some other items).  For that matter, vacuum sewage systems are routinely used on airplanes, trains and ships.  There are several "large scale" vacuum sewage systems in operation in Germany right now.

NASA houses the world's largest vacuum chamber to test Orion, which will take astronauts on the next mission to space and the moon.  This chamber is designed to simulate the stresses of space on the space craft to ensure that it will be able to withstand them.

The dentist or the dental hygienist will use a dental suction device on their patient. This way they can suck the saliva, blood and liquid drugs in the mouth of the patient.

In "clean rooms", there is often a carefully controlled air flow which is controlled by a vacuum.  In some places (like paint rooms) there may be small prep room participants must first enter to remove loose particles from their clothing.  This room applies a slight vacuum to do the job in the same way a vacuum cleaner works.

Vacuums are being used in the medical field to help with healing different types of wounds.  Applying a vacuum on animal wounds have shown that blood flow improves and excess fluids are more readily removed.  This, in turn, helps in the removal of bacteria.  Source:  The National Center of Biotechnology Information http://www.ncbi.nlm.nih.gov/pubmed/15943495

You can use a vacuum to aid in delivering a baby.  Instead of using forceps, a suction cup is attached to the head of the baby and out it pops.  http://www.aafp.org/afp/20000915/1316.html

After that baby is born, it needs milk.  A vacuum is used on cows as well as mothers to extract milk for later consumption.

Finally, we have to mention the Swedish-made device Austin Powers had in episode #1 (but don't ask me if they really work  ... they are not my bag, Baby).