(I'm new to this site, don't know whether 2 topics in one post are allowed but here goes)

Re: billb's proposed open acquarium + soap bubble experiment to demonstrate that CO2 doesn't expand rapidly to fill the room - I wish I'd thought of that when a pulmonary specialist (of all people) tried to tell my wife and me that CO2 is "lighter than air"! I've even read that claim in an elementary-level science book. I find this alarming! If a lie is propagated widely enough, it's accepted as common knowledge". I believe an excellent counter-offensive to bad school science is promoting science experiments at home. This would be greatly facilitated by the publication of good books for young experimenters such as were available in my younger days (50's-60's). We even had a newspaper columnist who published home experiments in the local paper. Perhaps you know of some currently available resources that you would recommend to your readers.

(While I'm at it, might as well try 3 topics)

Reply to poster asking "If electrons travel slowly, why does the light come on quickly?" (I hope I've quoted accurately, couldn't find the post when I looked back) -

To demonstrate heat, we heated the water, and predictably, the salt dissolved faster.

However, to demonstrate mechanical energy, we were instructed to stir the salt in the water. In retrospect, I don't believe this really demonstrates mechanical energy. All that is happening is that you are creating greater frequency of contact between water molecules and the salt. If you didn't stir, then you'd only have a puddle of highly concentrated salt water sitting at the bottom, which has a lower propensity to dissolve salt than a low concentration of salt in water.

Your article on traffic jams is very interesting to my mind. It closely parallels many thoughts I've had on the subject previously. Here in France road signs indicating "lane closed at 600m" seem like an invitation to French people to stay in lane until the very last possible tyre squealing second. Usually, I try to be the peace maker by creating space...which usually garners me no grace with the fastards behind me.

Being a recently qualified pilot I found your article on airfoils to be confusing, possibly due to the humour/ sarcasm which I didn't follow entirely. Obviously, that is not intended as a crticism of your fine site. Having been "taught" both theories by different lecturers and having had difficulty with both of them as theories I was much hoping that your clear presentations would help me. Sadly not. I'm ignorant and confused as ever.

Regards, Kevin.

A new misconception.... that you can balance an egg on end if you hold it still long and patiently enough for the yolk to sink to the bottom, thereby lowering the center of mass making the egg more stable. Actually, it is the albumin that sinks, being more dense than the lipid yolk. Prove this by setting an egg in a narrow beaker of vinegar and wait for the shell to react with the vinegar. You can then see inside the egg and see that the yolk is floating at the top.

Another, more immediate way to observe this is to separate several eggs. Add the whites from about three or four eggs to a graduated cylinder. Add only one of the yolks. The yolk floats on the top of the whites......... Doing is believing .......

I’m great fan of yours, and I love your site, it is just so inspiring.

I want to say something about the “gravity in space is zero?” part. You state that gravity is the force that pulls objects towards the Earth, but this is also a misconception. It is known in general relativity (at least to people that actually scrutinize general relativity) that gravitation is caused by space-time curvature that causes “mass”; bodies are closed together by the enclosing force of space-time reaching equilibrium of potentials. So gravity is rather a pushing force, not a pulling force.

While your article is correct in that light from the sun is not parallel, there is the unfortunate problem of light-scattering caused by the earth's atmosphere. Your examples prove only that there is atmospheric scattering, and not that sunlight is truly parallel in nature.
[Huh? My example is about the sun's surface, not about atmospheric scattering. Because each tiny point on the surface of the sun emits light in ALL DIRECTIONS, light from the sun as a whole is not parallel. The light doesn't act as if itcomes from a tiny point at the center of the sun. That's why the diagram says "wrong." If the earth had no atmosphere, my explanation would remain the same. -billb]

A different way of putting it is that the sun is a sphere, and light leaving that sphere goes straight. If all light from this sphere went directly away from the center of this sphere, then the only light the earth would get would be from an area on the sun smaller than the diameter of the earth itself! This would make for a tiny sun in the sky indeed it would like the earth seen eight light-minutes away. The apparent size of the sun matched with the amout of sunlight we can detect would therefore lead us to believe that the lightcoming from the sun goes in many directions, not just straight form the center and out (or perpendicular to the tangent of the apparnet surface of the solar body, if you want to get painfully technical).

"This is very different than the oft-quoted rule that "gases always expand to fill their containers." This rule only works correctly if the container is totally empty: the container must "contain" a good vacuum beforehand. However, we all live in a gas-filled environment. All our containers are pre-filled with air."

I would like tocomment on the problem you discussed with the "filled balloon/empty balloon" experiment. While it is indeed correct that the simplified explanation that is presented does not seem to prove that air has weight, your analysis of the problem is, like the experiment itself, not sufficiently involved. In truth the fact that a filled balloon weighs more than an empty one does prove that air has weight. You point out correctly that the balloon actually contains compressed air". However, this is the very condition which proves air has weight. If air did not have weight, putting more of it into the container viacompression would not increase the weight of the container and its contents. The analogy with living in a sea of air is also innappropriate because water, unlike air, is icompressible. Lifeforms totally surrounded by water could not perform the experiment because water cannot becompressed so that more could be forced into the container.

[ No, that's a very distorted version; it's not what appears in the texbooks. You have to go read some children's actual textbooks, then you'll see the problem. Read this part carefully:

Many books contain a incorrect experiment which purports to directly demonstrate that air has weight. A crude beam-balance is constructed using a meter stick. Deflated rubber balloons are attached to the ends, and the balance is adjusted. One balloon is then inflated, and that end of the balance-beam is supposed to sag downwards. A large amount of air supposedly weighs more than a small amount of air.

Thus, weight of Balloon A will be the same as Balloon B, if and only if our Hypothesis that air has no weight is true. When the scale is checked it will bcome apparent however that Balloon A and Balloon B do not weigh the same. This expressly disproves our hypothesis thereby rendering the hypothesis that air has weight to be true.
Dean Kimes <kitasiatattbicom>
Aurora, CO USA - Wednesday, April 30, 2003 at 09:28:21 (PDT)

The whole problem with this conundrum is that the "N" on acompass stands for "North-seeking end" not "North magnetic pole". Unfortunatly, "seeking" will not fit on acompass needle... hence to confusion over opposites attracting. Thecompass needle is facing it's "south pole magnetic end" toward toward the "North pole end" of the Earth's magnetic field... Rather than the Earth's field actually being switched - the compass needle has been mislabled for the sake of brevity.

[ Sorry, you're wrong. This is not open to debate; it's a very old physics standard similar to the standard for polarity of electric charge. We define "positive charge" as the charge on the proton. We define "north-type pole" as the pole of a rod-magnet which seeks the northern part of the Earth. The definition of "north-type pole" does not refer to the Earth, it refers to the poles of electromagnets. The definitions are part of contemporary physics and are even part of Maxwell's Equations. I assume that you've heard of the "right hand rule" taught in introductory electromagnetism courses. And because we've defined "north-type pole" in this way, we're forced to say that the northern part of the Earth contains a south-type pole. That way it can attract the n-type end of all thecompass needles.

Perhaps it would be better if things were backwards: if electrons were defined as positive charge, and if north-seeking magnet poles were defined as south-type poles. Unfortunately the physics standards both for "positive" and for "north" were adopted over a century ago and it's far too late to try to make them less confusing.

If you see a textbook which says differently, that textbook is wrong. There are lots of K-6 textbooks which get this wrong. I've yet to find any physics textbook at the undergrad level or above which make this fundamental error. - billb]

Julie Knapp <littleredhenschoolatyahoocom>
River Falls, WI USA - Tuesday, April 29, 2003 at 07:52:34 (PDT)

What about the Kasper wing? It has some curious properties.
Chuck jeronimo <chasjeronatyahoocom>
San Jose, CA USA - Tuesday, April 01, 2003 at 22:00:14 (PST)

I've read a lot on your sight..and although it addresses these issues, I just need it simplified, so students can understand...and so I can answer they're questions with answers rather that..."it's that way just because it is". Thanks!

[ The correct version of the "Bernoulli" explantion turns out to be identical to the "Newton" explanation. In other words, there's a pressure difference across a wing because the wing is deflecting air. And also, the wing deflects air because there is a pressure difference. This is one of those situations where two effects are connected together. They both happen at once, and one does not cause the other. They are both caused by air hitting a wing which has a tilted trailing edge. The tilt of the whole wing doesn't matter, only the angle of the wing's trailing edge is significant. Below is one way to understand it.

In order to generate a lifting force, the trailing edge of an airfoil must be sharp. Whenever air passes over any airfoil, the trailing edge of the airfoil determines the angle of air flow. The leading edge does not. This happens because air has inertia, and when the air flows away from the tilted trailing edge, the air keeps going in the same direction as the angle of the trailing edge. But the air ahead of the leading can approach the wing from most any direction. The leading edge doesn't control the approach of the icoming air. However, the air near the leading edge is greatly affected by the trailing edge, since the air is flowing off the trailing edge at a downwards angle. This down-flowing air stream gets in the way of any air which tries to flow horizontally under the wing. The air under the wing must slow down. Also, because the air flows off the trailing edge at a downwards angle, an empty pocket should form directly above the down-flowing air. However, a pocket does not form. Instead, the air approaching the front of the wing is pulled up and over the wing and it speeds up just enough to keep that pocket filled. The air above the wing flows very fast just as the air below the wing flows slowly.

V. K <vlkleinhathotmailcom>
Thunder Bay, ON Canada - Saturday, March 29, 2003 at 17:17:08 (PST)

[People who are threatened by those who point out mistakes can ALWAYS cry "nitpicker." But remember, you can't turn a valid complaint into "nitpicking" just by labeling it that way. Also, if someone starts ignoring errors and declaring them to be "nitpicking", it's very bad. It destroys the system of checks and balances and opens the door to any amount of errors at all. Click on all those links to articles about the shameful state of K-6 textbooks. The books got that way because the publishers are in the habit of saving face and making excuses rather than simply rolling up their sleeves and fixing the mistakes. Unfortunately, before they can fix anything they have to take responsibility and own up to having a problem in the first place. It's embarassing to admit to mistakes, but it's much worse to start covering them up in order to avoid public embarassment.

In truth, n/(small number) equals a large number, and n/0 is not a number, it's infinity. Your school made a genuine mistake. That'scommon and normal. Dismissingcomplaints is not normal, it's reason to fear that they've started playing "coverup" and stopped correcting mistakes, and if they did it with you, perhaps they've been ignoring lots of other complaints in the past. -billb]

Bobbi Kedzierski <bobbikedzieatyahoocom>
covington, ga USA - Sunday, March 16, 2003 at 22:40:08 (PST)

[ Bernoulli's equation works fine. We can explain 100% of the lifting force using Bernoulli, or we can explain 100% by using Newton's laws (after all, the Bernoulli equation is BASED on Newton's laws.) It's not Bernoulli that's wrong. The problem is with the "wing shape explanation" of lift; the one which claims that the parcels of air must race to the trailing edge in order to join together. It's also called the "popular explanation" or the "longer path explanation." It is wrong, since the parcels of air which are divided at the leading edge of an airfoil DO NOT rejoin at the trailing edge. They remain separate. Path lengths along the wing surfaces are not important in generating lift. In fact the upper parcel outraces the lower one and they never rejoin at all. The explanation is also wrong because a wing does not have to be curved on top and flat on the bottom (in fact, a symmetrical wing with equal path lengths flys just fine, it just stalls more easily than a cambered wing.) -billb]
A J Brislen <abrislenatdeltanetcom>
Laguna Niguel, ca USA - Monday, March 10, 2003 at 10:36:37 (PST)