The "denser air is pushed to the back" is wrong. Prior to acceleration the air inside the car has equal pressure at all points assuming nothing is either heating, cooling or blowing the air around. When the car accelerates the front window moves away from the air causing a low pressure area while the rear window move towards the air causing a high pressure area. The air then flows from the high pressure to the low pressure area thus moving the helium balloon. The density of the air remains virtually constant since no air is being pumped into or out of the car and the elevation is not changing unless the car is accelerating because it was pushed off a cliff.
There is no difference between your car accelerating, and a gravity field. So just as it does in gravity, the cold air sinks to the bottom, the warmer air moves forward, which is up, and being lighter than air, the helium is pushed to the windshield. It is true that there is air movement as the colder air separates from the warmer air. But if you could keep accelerating, you would see that the balloon still stays pinned to the windshield. Forward is up in this gravity field. http://www.physicsoftheuniverse.com/topics_relativity_gravity.html In any volume of air, what we measure is the average temperature. But in that are molecules with varying degrees of thermodynamic energy.
That does not address the point that I was making that your use of the term "density" was incorrect. It is the air pressure differential moving the balloon in the car. The only significant density differential is that between the helium and the air. Helium does not "defy gravity". Instead it has a lower density than air which causes it to "float" upwards through the air because there is less air pressure above the balloon than below it. The same principle applies to an air bubble in water. It moves against the direction of gravity because the air bubble has a lower density than the surrounding water and the water pressure above is lower than the pressure below. The air pressure in the car changes because of it's inertia when the car accelerates creating a lower pressure at the front of the car which causes the lower density helium to move towards the lower pressure air. Braking does the reverse because the air inside the car now has momentum and when the car decelerates the air inside continues to move forward creating a higher pressure at the front and a low pressure at the back. Same thing happens when the car turns left or right.
The same is true for molecules having a higher degree of thermodynamic energy than other. That is why it begins to separate by density, hence, temperature. It is the same principle by which a centrifuge works. I was being loose with the language but the principle is correct.
If we have 1 amp flowing in a 10 gauge wire, what travels faster through a wire: Electrons or sound waves?
As I understand it, electrons are coming in and out of existence all the time due conversion between mass and energy. So, what would happen is what we know as our universe. If an electron instantly appeared in my coffee cup due to natural processes, I'm not sure what THAT would mean.
For any natural process there is a delta t. In this case we assume that an electron instantly appears from nothing.
OK. Well, I'd say that the electron represents a certain amount of energy equivalent. So, if the electron suddenly appeared due to natural processes it would mean we have an electron, but are slightly cooler by the energy equivalent of an electron. If an electron were added in its entirety (that is, not as a result of natural processes) then that is an addition that would be a warming.
I think it's fair to consider this an example of floating, which is usually defined in terms of relative density.
Sound waves. I remember working out the problem long ago, and being surprised at how slow the electrons move. Let me try it again. 10 gauge wire has a cross sectional area of 5.4 mm^2, or 5.4 E-2 cm^2. Call that X. Copper contains 8.5 E+22 atoms/cm^3. Assume one mobile electron per copper atom. Call that Q. 1 Amp is 6.25 E+18 electrons/sec. Call that A. Speed = A/(Q*X) = 6.25 E+18 electrons/sec / (8.5 E+22 electrons/cm^3 * 5.4E-2 cm^2) = .0013 cm/sec So, the electrons are actually moving with a sludge-like slowness.
Impressive! I knew the answer, but I didn't have the poop to back it up. (Don't tell my electrical engineering professor father!)
Q19: What relatively easy demonstration allows you to add two somethings together and get absolutely nothing? Hint: How many real vector quantities can you name? By "real" I mean something that can be measured. I had a friend who was scientifically inclined but couldn't believe this really happens. Because when you add the vector quantities of two things, nothing is left - nothing at all! He couldn't believe that you can take two real things, add them together, and have nothing at all. I did a table-top demonstration so he could see it with his own eyes.
Before anyone interested drifts away Answer: The Interference of light. In a two-slit diffraction demo, when you block one slit, light appears where there was none, When you open the slit allowing the light from the two slits to interfere, the light disappears in places where it was. So by adding two real things together - the two EM fields - you are left with absolutely nothing.
A: The bearing in the hard drive. They use a virtually frictionless, ferromagnetic fluid bearing. Ferromagnetic fluids work by introducing into a fluid what is essentially iron dust. The dust is so fine that Brownian Motion keeps it permanently in suspension. This allows the fluid to be controlled with magnetic fields, like a metal.
But remember that this observation happens with all waves such as waves on a sea, and sound waves interference cancellation is even more dramatic. The physics is obviously different but the observations are the same. Light interference is more interesting from the physics point of view
A wave in the ocean is just a disturbance in the water. If two water waves interfere you still have water. An EM wave is not a disturbance in an existing medium. And it produces particles. If the ether existed it would be the same type of phenomenon. But as we found out over a century ago, there is no ether.
Q23: What physicist stood on his head and peed in front of his peers, in order to prove you can pee in space? - Richard Feynman It was argued that humans need gravity to pee. Feynman, in his never-ending elegance, disproved this hypothesis in a minute. Q25: What would happen if an electron instantly appeared somewhere in the universe? The associated magnetic field goes as the rate of change of the electric field [Maxwell's Equations]. If an electron appears instantly [in zero time], the rate of change of the electric field is infinite. So an infinitely powerful magnetic wave would propagate out and destroy the universe.
Q22: What is the mechanism of action proven to be the cause of "spooky action at a distance"? A: We don't know. That's why it's called spooky action at a distance! There are popular hypotheses that seek to explain this - Bohm Theory, The Many World's theory, perhaps String Theory...[not sure about that], but at best, any mechanism of action to explain effects like instantaneous spin conservation between entangled particles, even at vast distances, is purely hypothetical, and generally exotic. I'm pretty rusty on this, but I remember that Feynman was famous for a calculation in which he showed that an electron set in motion must be considered over all time, in order to account for all observations. In other words, in mathematical terms, it implies... suggests... connotes that what happens now depends on what happens to the electron in the future. And this comes from Quantum Electrodynamics - a well established field and a subject invented by Feynman. Spooky stuff! It always frustrated me that for things like this, what I consider to be the coolest of all because they are mysterious, many physicists say, so what? We know what happens - Quantum Mechanics is right every time. Who cares how it happens? Really?!?! This is fundamental. It may be the key to a much greater theory of physics.
Hmm, that was sort of my answer in post 133 "God only knows" It is cool and I read a recent article about a practical use of it in transmitting secure data but can't remember any of the details.
