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Chap 2 (fluids) archived stories part E

Friday, February 06, 2009

For Chapter 2, this is part D of the new stories and also the updates to the items in the book, including many video links and journal citations. If you want all the video links (hundreds) and journal citations (thousands) for this chapter, go to

http://www.flyingcircusofphysics.com/pdf/Chapter2_Ref_Com.pdf

First, a list
--------- New items (not in the book):
2.176 Pub trick --- egg tricks
2.177 Pub trick --- raisin in champagne trick
2.178 Pub trick --- oil blobs in water
2.179 Pub trick --- piercing a plastic bag of water with a pencil
2.180 Pub trick --- bottle cap blown into bottle
2.181 Fake video --- free standing water
2.182 Controlled breach of the Condit Dam
2.183 Pub trick --- separating two pub glasses
2.184 Pervious concrete
2.185 Fly in gun blast
2.186 Attack of the tumbleweeds
2.187 Pub trick --- Pouring a rainbow
2.188 Poured art
2.189 Escape from a sinking car

Now the stories:

2.176 Pub trick --- egg tricks
Jearl Walker www.flyingcircusofphysics.com
July 2011 Here are three pub challenges involving hard-boiled eggs.

Separating the egg from the shell. The common way is to knock the egg against the table and then peel the cracked shell from the egg. However, this procedure is frustrating because it is slow and usually requires picking off small bits of the shell. Is there any better way, a way in which you can separate the egg and shell in a few seconds?

Egg into a bottle. Once the shell is off a hard-boiled egg, position it with its sharply-curved end down on the opening of a fairly wide bottle (wider than a beer or soda bottle, but narrower than the egg). Can you make the egg go into the bottle without cutting the egg up into small pieces?

Egg out of a bottle. Once the egg is in the bottle, can you get it out without breaking the bottle?

Answers:

Tap each end of the egg on the table so that an end piece can be removed, each about the size of a small coin. Roll the egg over the table so to crack it and to separate the egg from the interior surface of the shell. On the end with the smaller opening, encircle the opening with your thumb and index finger, press your mouth snuggly against the thumb and finger, and then blow hard. The egg should pop out the other opening. No hard physics here ---- on your end of the egg you increase the air pressure above the atmospheric air pressure on the other end. The pressure difference shoves the egg through the larger opening. Because the egg is an elastic solid, it can be distorted enough to slide through the opening without being ripped apart.

http://www.ebaumsworld.com/video/watch/563310/

To get the shelled egg to slide into the bottle, drop a bit of burning paper into the bottle and then position the egg over the mouth, pressing down on it slightly to get a tight seal. While you are moving the egg into place, the fire heats the air inside the bottle, causing it to expand. Some of that air is forced out of the bottle. As the fire burns out (due to the elimination of the paper or the oxygen in the bottle), the air remaining in the bottle begins to cool, which causes the air pressure to decrease. The air pressure on the lower end of the egg is then less than the atmospheric air pressure on the top end of the egg, and the pressure difference shoves the egg into the bottle. Again, the egg can squeeze through a narrow opening because it is a fairly elastic solid.

http://www.youtube.com/watch?v=xZdfcRiDs8I

To get the egg back out of the bottle, tilt the bottle up so that the egg slides down near the opening. Then blow hard into the bottle. As you blow, the air lifts the egg away somewhat, but as soon as you stop, the egg slides back into place near the opening, sealing off the escape route of the air. The air pressure on the top end of the egg is then greater than the atmospheric air pressure on the bottom end, and the pressure difference shoves the egg through the opening.

http://www.youtube.com/watch?v=_JBOX116Pzw

more links
http://www.wimp.com/dofaster/
http://www.youtube.com/watch?v=SHWRGP-PpHQ
http://chemistry.about.com/b/2011/02/03/egg-in-a-bottle-demonstration.htm
http://www.doscience.com/act_archive/home_activities/egg_suck/egg.html
http://www.wikihow.com/Blow-the-Shell-off-a-Hard-Boiled-Egg
http://www.thriftyfun.com/tf777352.tip.html
http://www.youtube.com/watch?v=Fhz4xsJ1LUo

2.177 Pub trick --- raisin in champagne trick
Jearl Walker www.flyingcircusofphysics.com
August 2011 If you drop a raisin into water, it simply sinks to the bottom and is rather boring. But if you drop it into soda, clear beer, or champagne (for those special times when the celebration requires a raisin or two), the raisin will repeatedly move up and down. Here is a video taken when apparently the excitement required a raisin:

http://www.wimp.com/raisinchampagne/

The champagne (or soda or beer) has lots of dissolved carbon dioxide. Some of those molecules can come together to form bubbles (the characteristic bubbles of champagne) but they need some nucleating site for the bubble formation. The bubbles cannot easily form in the liquid itself because such a bubble is initially tiny with a large curvature of its surface. That large curvature means large surface tension, which collapses the bubble. So, although the bubble tends to expand by collecting more and more carbon dioxide molecules from the liquid, it is almost immediately collapsed by the surface tension.

Instead the bubbles form in tiny crevices on the glass surface or on contaminates lying on the surface, or, in the case of our party girl and her glass of champagne, on the surface of a raisin. In such cases, the initial is not spherical but is down inside a crevice, and the crucial feature to its survival is that its surface with the liquid is not highly curved but only slightly curved. So, the surface tension is not large enough to immediately collapse the bubble. Instead, it remains in place as more and more carbon dioxide molecules pass (diffuse) into it. Eventually it is large enough that it is no longer in danger of collapse, even if the curvature of its surface is large.

As bubbles form and then grow on the raisin, they produce an upward buoyant force that is large enough to bring the raisin to the champagne’s upper surface. As soon as the raisin reaches the air, many or most of the bubbles pop open and release their carbon dioxide. Thus, the raisin loses much of it buoyancy and sinks to the bottom of the champagne. This cycle repeats until the champagne loses most of its dissolved carbon dioxide (goes flat) and bubbles stop forming.

If you want to experiment, try various seeds and other small objects in a carbonated drink. Or, using a carbon dioxide dispenser as is now commercially available, carbonate a glass of water.

http://www.youtube.com/watch?v=T0wr2U0p-xQ
http://www.youtube.com/watch?v=zxMBrmicycw&feature=related
http://www.youtube.com/watch?v=iQJzlpwcU2Q&feature=related

References
Dots · through ··· indicate level of difficulty
Journal reference style: author, title, journal, volume, pages (date)
· Stavrinidis, V., “Dancing lemon seed,” The Physics Teacher, 40, 286 (May 2002)

2.178 Pub trick---oil blobs in water
Jearl Walker www.flyingcircusofphysics.com
January 2012 Here is another trick from the delightful book by Eric Muller of the Exploratorium in San Francisco. Pour enough water into a clear drinking glass to fill it to about 75% capacity. Then pour in salad oil to make a layer about 1 centimeter deep. (Muller suggests olive oil or sesame oil; I used peanut oil.) The oil floats on the water because it is less dense than the water. The challenge is to make blobs of the oil descend into the water and then rise back up to the oil layer, without your touching the glass or stirring the contents.

Here is the answer: Sprinkle salt into the glass. Salt grains are denser than both oil and water and thus will sink through the oil and then begin to sink in the water. As they move through the oil layer, some of the oil clings to the salt grains and is pulled downward with them. The descending oil is in blobs surrounding salt grains.

As the grains descend, then also begin to dissolve, and then salt molecules (sodium chloride) diffuse (spread) through the oil. As the molecules begin to diffuse out of a blob and into the surrounding water, the density of the oil blob decreases until it is less than that of water. Then the blob floats back up to the oil layer, merging with it.

When I heavily sprinkle salt on the oil layer, a dimple forms on the top surface, under the weight of the salt. I can then see salt grains drawn into the dimple and down through the oil, where another dimple forms on the water-oil interface.

The blobs that break free of the oil layer and descend through the water to the bottom of the container are noticeably opaque because of the salt grains they hold. But as a blob sits on the container bottom, its top portion clears because the salt descends to the bottom of the blob. When a blob breaks free of the container bottom and begins to ascend, it is noticeably clearer.

If I adjust the illumination correctly, I can see a downward flow of the water along the center even when there is no blob activity. Salt molecules are entering the water from the oil in that region, and the heavy salty water then descends. When a blob breaks free of the container bottom and bobs back up to the oil layer, it can leave a trail of descending salty water along its path.

If I add enough salt to the glass container, all this action noticeably slows down or even dies out. The salt concentration in the water is then so large that the salt molecules in a blob will no longer diffuse out of the blob and thus the density of blob does not change. The show is then over, and if you are doing all this in a pub or restaurant, maybe it is time to leave before the owner sees the mess you have made.

Reference
Muller, E., While You’re Waiting for the Food to Come: Experiments and tricks that can be done at a restaurant, the dining room table, or wherever food is served, Orchard Books (1999)
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2.179 Pub trick --- piercing a plastic bag of water with a pencil
Jearl Walker www.flyingcircusofphysics.com
March 2012 Partially fill a plastic food bag (such as a Ziploc bag) with water and then seal it (close the interlocking plastic ridges and grooves at the top). Can you tear the bag below the water line without losing any water?

A similar question was asked at the onset of World War II by everyone flying aircraft over enemy territory (on both the Allied and German sides). If ground fire hit a fuel tank, the hole would allow fuel to leak out, which would limit the flying distance. Even more important, the leakage could cause a fire or explosion. The leakage was especially a problem where a round exited a tank, because its penetration into the tank probably set it tumbling and thus it would rip out a larger hole at the exit point than at the entrance point. One obvious solution was to attach heavy plates to a tank, to stop the rounds, but the large, extra weight was just impractical on any long-range flight.

The acceptable solution for the Allied aircraft was to line the tanks with a strong fabric layer and then several layers of a treated (vulcanized) rubber and untreated rubber. When a round pierced the multiple layers and allowed the fuel to wet the untreated rubber, that layer would swell so much as to cover the hole and thus eliminate (or at worst, greatly diminish) the fuel leakage. Of course, the system was not perfect, but it did give the pilots a better chance at completing a mission and returning home safely.

Something similar happens with the pub trick with a Ziploc bag except there is no swelling. Take a sharp pencil and ram the pointed end into and through the lower part (water-filled part) of the bag. The pencil can rip a hole through both sides of the bag without any water spilling out.

http://www.wonderhowto.com/how-to-do-amazing-pencil-pierce-trick-plastic-bag-filled-with-water-398694/

After the pencil point penetrates the front of the bag and as progressively thicker portions of the shaved, cone-shaped region pass through the opening, the pencil grabs the perimeter of the hole and pulls it into the water. This action stretches the plastic around the perimeter. When the pencil stops, this stretched plastic hugs the pencil shaft so tightly that water cannot leak out around the shaft. The hole is sealed down onto the shaft.

When I pull the pencil backward so that point leaves the far hole, water (of course) pours from that hole. When I push the pencil back through the hole, I can see how the upper end of the shaved portion again grabs the plastic around the hole and stretches it, resealing the hole.

The water serves two purposes: It demonstrates how well the hole is sealed and it adds bulk (mass) to the bag so that a sharp blow by the pencil allows the pencil to penetrate the side. I find that pint and quart freezer bags, with their thicker plastic walls, work better than the sandwich bags, with their thinner walls. (My family was amused with my frequent failures with the sandwich bags.)

Of course, there is a limit to how far below the water surface the pencil can be used. If you have a fairly tall column of water, the water pressure near the bottom will be enough to push water outward between the plastic and the shaft. If you investigate this pub trick with a tall column of water, let me know what you find.
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2.180 Pub trick---bottle cap blown into a bottle
Jearl Walker www.flyingcircusofphysics.com
April 2012 Take the cap from a beer bottle (or the drink of your choice), bend it over onto itself (you might need pliers), lay the bottle down on a table, and then place the bent cap in the neck of the bottle. The challenge is to blow into the bottle so as to push the cap into the rest of the bottle.

If you simply blow into the bottle as instructed in the challenge, the cap flies out of the bottle, not farther into it. Here is a video demonstrating both the unsuccessful method and the successful method of meeting this pub challenge.

http://www.youtube.com/watch?v=IP1Xy9CPwRY

As the video performer explains, simply blowing into the bottle sends lots of air past the cap and into the rest of the bottle. This incoming air effectively turns around and comes back of the bottle (because of the increased internal air pressure). That outflow of air pushes the cap out of the bottle.

I can add to the explanation. When you bend the cap onto itself, it is bent around a diameter. When you then put the cap in the bottle neck, it can sit only with that diameter along the length of the neck, not across the width of the neck. This orientation means that the cap presents only a small cross sectional area to the air that is blown into the neck. Most of that air stream passes over the top of the cap. Thus, the air stream that comes back out of the bottle must be along the lower part of the neck and thus right up against the cap, pushing it out of the bottle.

Try replacing the cap with something with a larger cross-sectional area in the incoming air stream. Or put tape around the cap several times to increase its cross-sectional area. Do you find that the cap still flies out of the bottle? Or, when the cross-sectional area is large enough, do you find that the cap moves into the rest of the bottle?

http://www.metacafe.com/watch/1083530/bottlecap_trick_cool_bar_bet/
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2.181 Fake video --- free standing water
Jearl Walker www.flyingcircusofphysics.com
April 2012

At least 6 million people have viewed this video in which a young man seemingly suspends water in midair until he pricks it with his finger (well, he actually never touches the water). He first fills a glass with water, places a card over the open mouth, inverts the glass while holding the card in place, places the inverted card and glass on a table, and slides the card out from beneath the card. A bit of the water spills from the glass during that last part. Then he yanks the glass upward while giving it a twist. The water stays exactly in place.

http://www.youtube.com/watch?v=7ctaA2mERzI

A lot of curious things can happen in the physical world, especially in quantum physics. So, some people are quite willing to throw away any common sense when watching a video like this. They something like, “Well, anything is possible. Maybe the twisting somehow turns off gravity or makes the water rigid and no longer fluid.”

Yes, well, there is a lot of stuff in quantum physics that defies my everyday experience, but water is not weird. I’ve using it for decades. I bathe in, swim in it, stir it for tea, and clean my clothes in it. Never once has swirling the water solidified it. Other than freezing it, there is nothing I can do to transform it to a solid.

There is also nothing I can do to turn off gravity. Every time I stumble and fall, as I fall I always scream out, “Off! Off! Gravity off!” Alas, the command has never been met—I have always landed hard. The only consequence of my screams is that everyone around me is quite uninterested in helping me up. In fact, they always move away from me as quickly as possible, usually with wary glance back over one shoulder. Perhaps they are worried that if I could somehow turn off gravity, we all would float into space. Well, probably it is just the screaming.

One of the strongest arguments for everyone studying science in school (physics included) is that everyone needs to build up a credibility checker. Educationalists call it “critical thinking.” However, I think we could just call it “avoiding someone making a fool out of you.” Then if someone shows you a video in which water seemingly defies gravity, you immediately know it is faked.

http://www.youtube.com/watch?v=W3pzh6-nLyY&feature=related
http://www.youtube.com/watch?v=Du7eibJVDXA

2.182 Controlled breach of the Condit Dam
Jearl Walker www.flyingcircusofphysics.com
August 2012 In 2011, in south central Washington, a tunnel was drilled through the Condit Dam on the White Salmon River, which feeds into the Columbia River. For environmental reasons, the dam was no longer economically viable and the power company running the hydroelectric system there decided to remove the 1913 dam and re-establish the White Salmon River. When the tunnel breached the dam near the base, the water pressure on the lake side of the dam propelled water through the tunnel, moving not only the water but about 1.6 million cubic meters of lake sediment through the tunnel in about six hours. Here is the dramatic video by Andy Maser, who is an acknowledged cameraman, producer, and film edito. (Press the advance button to start the video.)

http://vimeo.com/31305629

The explosive flow was due to the hydraulic head on the lake side of the tunnel: The water there was about 38 meters deep, which created a pressure near the bottom of about 0.37 million pascals (about 3.7 times atmospheric pressure).

In the video, note how the first rush of water is clear and thereafter it is deeply blackened by the sediment, with blackened water rushing under the clear water and then rising in front of it. Here is a screen capture from Maser’s video:

Also, note the hydraulic jump (or bore) where the flow has a stationary high point just downstream of the flow. Another screen capture:

http://www.nationalgeographic.com/explorers/bios/andy-maser/ information about Andy Maser

http://andymaser.com/ Condit Dam National Geographic Society

http://www.dump.com/2011/11/page/25/ scroll down to Nov 6