Fill a cup with very cold (preferably almost freezing) water. Fill another cup with very hot (preferably almost boiling) water. Now stand at your kitchen sink, and from as high as you can reach, slowly pour one cup into the sink, listening carefully to the sound it makes. Now pour the other. The cold water makes a high-pitched “splish-splash” sound. The hot water, however, makes a very low-pitched “thumpy” sound, with almost none of the high-frequency noise that cold water makes. WHY?
Jim Horn replies: “I’d guess because cold water has several times the viscosity of hot water (the ancient Egyptian water clocks had sides that tapered differently for the day versus the night as the water dripping out at night was colder - more viscous - didn’t flow as quickly). The more viscous (physically harder) and denser cold water would splash differently than the hot stuff. Make sense?”
Hmm. But if cold water is more viscous, shouldn’t the cold water be making the thumpy sound? I mean, listen to the difference between pouring pure water and water in which so much sugar has been dissolved that it has become almost syrupy (very viscous). What’s going on here?
[Update in 2008: Robert Zane at Irvine Valley College has supplied me with the answer! I'll upload it here for all to enjoy ASAP. Thanks, Robert! -jkh-]
Why did the Hale-Bopp Comet have two tails? Don’t tell me “outgassing”. I don’t buy it. The solar wind is a great deal faster than any comet’s outgassing could be, so comet gas all gets swept up into one tail. If the outgassing had some spectacular kind of thrust, then... why?
Jim Horn replies: “There are several ingredients in the tail. Much is simple dust particles which are blown away by the pressure of the solar wind. That’s the Dust Tail most of us saw. A significant portion is ionized gasses which, having an associated charge, is affected by the local (solar) magnetic field and strongly tends to spiral along same. That’s the much dimmer blue Ion Tail. What’s news about H-B was that a third tail between the two of sodium ions was discovered. Seems the sodium had less charge for its mass than other ionized gasses so followed a path between the other two.”
Cool. Thanks, Jim. I’m not worthy. Okay, move this one onto the “Answered Questions” page.
Related info about Comet Lemmon in 2013 .
Why is the human race getting stupider overall? Test scores worldwide continue to get lower and lower. All grade schools used to teach fractions in 4th grade; now they wait until 5th grade because the students “just can’t handle fractions in 4th grade”. All high schools used to include the Quadratic Formula in Algebra 1; now it’s not seen until two years later! In the late 19th century, a course in “algebra” included number theory, and was often taught in 8th grade. Now you’re lucky to learn number theory at any level of education. Political elections have been reduced to popularity polls, with the winners not being the best person for the job but the person with the cutest TV image. We cower to accusations of being “socially insensitive” and allow morons with illogical agendas to reshape our language. Have we perhaps gotten so stupid that we are no longer even able to tell how stupid we’ve become?
Jim Horn replies: “Duh - I dunno. But if I’m elected I promise to select a group to study the problem. My personal opinion is that modern communications has allowed us more mental challenge than ever before - but we’ve used it to replace our thinking more than ever before. I am right on this - you don’t have to think about it much.”
On a more serious note, Alan Altany of Marshall University has some very deep thoughts on this topic in his essay entitled “Modern Science, Religion and the Diminution of Intelligence” .
Contrary opinion: John Wilson emailed me a reference to “The Flynn Effect” which may indicate that humanity is in fact getting smarter. Thanks, John! I done feel smarterer already!
Fill a glass jar with tap water, leaving only a little bit of air at the top. Put it in your freezer, and leave it there until just before it begins to freeze. It takes experimentation to find the precise timing; be careful that it doesn’t actually freeze far enough to burst and make a mess in your freezer. Once you have the timing down, take the jar out of the freezer and slowly turn it over and back again to convince yourself that it’s still 100% liquid. Then rapidly twist, shake & spin the jar in your hand, causing as much motion of the water as you can. In just a few seconds, you’ll see the water turn white as it suddenly fills with floating ice crystals, which rapidly cascade into a jar full of slush. If the water is cold enough, it’ll freeze almost solid. The strangest thing I ever saw was once when I took the jar from the freezer, took the cap off, and poured some of the water into a glass. It poured clear and smooth, but the glass was filling up with slush! Question is: why does this happen?
Jim Horn replies: “Cool!!! (Yes, literally, too) Y’all rediscovered ‘supercooling’. It turns out that most material phase change temperatures are well defined but it DOES require something to trigger the change itself. In other words, liquid water, if really pure, can be cooled to as low as 40 degrees below zero without freezing. Then if anything triggers the freezing process, look out! This little tidbit has killed lotsa airplanes - many clouds at freezing temperature still have liquid water drops just waiting for a freezing trigger. A collision with an airplane’s wing/propellor/engine provides just that. And the airplane grows INCHES of really gnarly ice in moments and falls down.
“A similar event at the other end of the scale is superheating - taking water above 212°F (100°C) at sea level without it boiling. Often happens in Microwaves - heat a cup of water, dump in the cocoa mix, and scald the !@#$%^&* out of your hand as the mix bursts over and out of the cup.”
Dude! Move this one to the Answered Questions page too.
Matt Brounstein asks, “When a videocassette says This movie was reformatted to fit your TV, how do they know what size my TV is?” This parallels James Smith’s comment, “When a radio station says, for example, You’re listening to KFI, how do they know?” My favorite is the sign you see in airports and shopping malls that announces You are here. Amazing! How did they know?!?
Actually, now that I think about it, the sign is wrong most of the time! All those signs that say You are here are in fact incorrect right now, because I’m not there. Those signs are only right when I happen to be there, which is rare. So I propose, for the sake of greater accuracy, that all such signs be changed to say You are probably elsewhere.
Dr. Stephen Thomas asks, “Why will a sign — such as in caverns, at construction sites, etc — read WATCH YOUR HEAD and yet not provide a mirror?”
Fred Lipschultz mused: “It reminds me of what the cabin attendants say when one lands: We’d like to welcome you to (such-and-such) airport. I wonder if they’ve ever said something like the following: We’d like to welcome you to Los Angeles International Airport... but unfortunately we can’t since we’ve landed at Long Beach International.”
The unanswered question, of course, is why does the human brain enjoy silly conundrums (conundra?) like these? An even deeper question is: why do some people take much longer than others to recognize a joke?
At Richard Nelson’s house many years ago I inadvertently started a debate which has never been settled. Since it had been a very hot day, it was proposed that an electric fan be placed in a window to blow cool outside air into the house. Brian Walsh, an expert in air conditioning and such things, said that it would cool the house faster if the fan were turned around, blowing outwards, thus pulling cool air in through all the other windows of the house. I then proposed that the fan would push more hot air out of the house if it were placed not in the window but about a foot back, blowing towards the window. I figured that this would exhaust not only the air blown directly through the fan but also some of the air that it passed, by a kind of Venturi effect. All present came unglued and agreed that I was completely insane. I proposed a test of my hypothesis: hang a strip of paper in a doorway so that the amount of airflow could be judged by the angle of the paper. Much to the amusement of everyone except me, this was done, and the fan was moved between the two proposed positions. The test unfortunately was inconclusive, since the fan was not powerful enough to move the strip of paper very much.
It all happened in the mid 1980’s, and to this day I get ribbed about my silly electric fan idea.
The question is: how could my hypothesis be tested reliably without fancy airflow measuring equipment? To this day, however, I place my own electric fans back from the window about a foot...
UPDATE: The answer has been found! And it’s VERY simple! In brief, to see if there is a sufficient Venturi effect happening, all you have to do is pretend that the space between the fan and window is a large invisible Venturi tube, and tap into it! Here’s what I mean. It’s fast & easy. Just hang a small strip of paper directly between the edge of the fan and the edge of the window. If the strip is pushed outwards (away from the fan-to-window line), then some of the air going through the fan is NOT going through the window but is being diverted back into the room, which means that the fan’s position is worse than if were mounted inside the window frame. On the other hand, if the strip is pulled inwards (towards the fan-to-window airstream), then the airstream created by the fan is sucking air from the room along with it and both are going out the window, which means that the fan’s position is better than if it were mounted in the window frame.
The verdict: It depends on several factors, but mostly on the velocity of the airstream. If the fan is one of those typical home-style el-cheapo fans that make lots of noise but don’t move much air, then it’s best mounted in the window frame. On the other hand, so-called “air circulator” style fans, with strong rugged motors and efficient fan blades, are capable of creating an “invisible Venturi tube” when aimed at an open window about a foot away or so. The reason is simple: All Venturi tubes only begin to exhibit the Venturi effect when the airstream within it is above some given threshold. Blow slowly into a Venturi tube, and the air pressure at the middle is HIGHER than the air pressure at the other end. But blow fast enough, and the inside pressure drops BELOW the pressure at the other end.
To my chagrin, I must therefore confess that THEY were right ABOUT THAT PARTICULAR FAN, since it was in fact made by the El Cheapo Fan Company, cooling not by the Venturi Effect but primarily by the Placebo Effect. However, with smug satisfaction, I must also point out for the record that my initial hypothesis is correct regarding REAL fans. Any “air circulator” fan, set to its highest speed, will push more air through an open window when placed NEAR the window than when placed IN the window. It uses the non-moving air in the room as a Venturi tube through which it punches a column of rapidly moving air. The invisible sides of the Venturi tube are of course sucked inwards and blown out the window along with the air that passed through the fan.
OOH! OOH! It just hit me! The above implies an even simpler answer to the original question! All you need is a barometer placed anywhere in the room! If the barometer DROPS when the fan is moved back from the window, then the fan is pushing more air outside than it is moving through itself. If the barometer RISES, however, then put the fan back in the window... or go buy a real fan!
Hooray! Another “Unanswered Question” gets moved to the “Answered Questions” Page!
Black holes are often described as almost-invisible deathtraps hungrily awaiting the unwary space traveler, as in this
comic stripgraphic novelette:
But couldn’t a spaceship use the “Unruh Effect” to detect an approaching black hole? A mirror facing the direction of travel produces an increasing number of virtual photons when approaching a black hole. Could they be detected early enough to take evasive action? If the direction of the photons were taken into account, could evasive maneuvers be automated?
Will such a black-hole detection-and-avoidance device be called an “unruh”? What Star Trek episode will first use a defective unruh (while approaching a Kerr Hole ) in its plot? Of course, the resulting uneven time dilation would cause the theme music to get louder and louder as the suspense builds, but in the last minute of the episode they’d all suddenly remember that sweeping the ship with a broad beam created by crossing the replicator, the holodeck, and the transporter all through the Heisenberg Compensator would not only escape the Kerr Hole but also reactivate the unruh which would detect that it was really a binary hole and the unruh would make them just barely escape the other hole while the camera moves in for a closeup of the Captain’s face as the credits begin to roll...