swansont

At 25, you're near the point where cellphones have been readily available for most or all of your teen+adult life. When I was your age, as part of the preceding generation, there were car phones if you were really well-to-do, that were about the size of shoe and not particularly portable. That's probably why they are more ubiquitous with the under-30ish crowd. It's also a heck of a lot cheaper to get your teenage their own phone number than it used to be with land lines.

Re-read why Kyrisch wrote — you had set them to be opposite, and Kyrisch was correcting that. graqvity is the centripetal force ONLY at the top of the loop, and in the condition that there is no normal force. In general, gravity will be one contributor to the centripetal force at the top and bottom of the loop, because those are the only places it is directed along the radius. At other places it will contribute both a radial and a tangential acceleration, so the object will be changing speed. (Conservation of energy also tells you this, so you can use either one to see how the speed changes.)

You have to remember that the description of how the body works will have to vary from frame to frame. Most of the values you might measure are not invariant, so they will be different in each frame. So if you were able to measure pulse and blood pressure from your frame somehow, it would not be the 80 and 120/80 that is measured in the astronaut's frame. You might conclude that the astronaut's sphygmomanometer was off, much like his clock was off in measuring the pulse. But once you get past time and distance, it gets even more convoluted in trying to figure out the transformations.

To clarify, you can PM any mod if you request to reopen the thread for the purpose of discussing evidence. However, it must be for that purpose

I agree. Often the best approach is to define the system such that you minimize the sources and sinks. Keep it simple.

Or, as I have said on occasion, saying that something is moving without giving a reference is equivalent to asking, "What's the difference between a duck?"

I'd imagine that the ability to pump gas for evacuation takes priority anyway. Merged post follows: Consecutive posts merged That's why I would not want a work cell phone, and don't give out my number. The cell phone I have is only turned on when I travel. When my answering machine broke down I did not replace it (95% of the messages were spammy, even though I'm on the do not call registry. Polls, charity and political messages.). If anyone I know wants to leave a message, they can email me.

The corded phone is because I have a land line, not why I have a land line. I just hate cell phones (and have a mild dislike of phones in general), and only have one for emergencies because pay phones have pretty much gone away.

Maxwell proposed it, but I think it wasn't fully accepted until Hertz produced and analyzed radio waves in the late 1880's.

The energy goes into other forms. The putty will heat up, there is work done in deforming it, and any sound you hear contains a small amount of energy. Total energy is conserved.

Land line and still have a corded phone, because that works when the power goes out.

No, it's not. But it wasn't a known contradiction until scientists realized that light was an electromagnetic wave, and that this had implications on kinematics.

That was not the view pre-relativity. Merged post follows: Consecutive posts merged It's a consequence of Maxwell's equations, once you realize that light is an EM wave. Einstein applied the concept to kinematics — his paper was call On the Electrodynamics of Moving Bodies (well, technically it was the German equivalent of that, Zur Elektrodynamik bewegter Körper)

Not synchronized — the clock will be behind the Master clock. (I prefer that term to universal) It will run at the same rate when it's in the same inertial frame, which means it is syntonized, but it will not read the same number. Synchronized means same rate and same reading, i.e. synchronized ideal clocks remain synchronized if unperturbed.

When 2 particles collide there is a force between them. By Newton's third law the force A exerts on B is equal in magnitude and opposite in direction to the force B exerts on A. However, unless you know what the force is, and how long it is applied, it won't help you to solve for the motion of the objects, which is why momentum is a useful quantity in collisions.

That's why you can treat such a situation as the ball experiencing an external force — modeling the earth as an unmoving, effectively infinite mass is a reasonable approximation of reality.

It's a consequence of the nature of the conjugate variables. The wavefunctions (e.g. for position and momentum) are Fourier transforms of each other. And experiments show this as a real effect. The entities in question really are smeared out in position and/or momentum — it's not an artifact of being limited by instruments.

A two-photon reaction from counter-propagating beams would not violate conservation of momentum. So unless there's some other restriction that I can't think of, that could work.

Ask him if they exist and have not been disproven.

A generator is an obvious answer. Many motors can be run in reverse to act as generators.

Blocking or Flyback oscillator, probably. Camera flashes use one. I would imagine circuits and explanations for those can be found online.

The absorptions are to virtual states, so I'm not sure if they follow rules for real absorptions. For a real electric dipole transition, the lifetime varies as [math]\frac{1}{\omega^3}[/math] so if the transitions follow this: since dispersion tells us that higher frequencies are slowed more this implies that the higher-frequency transitions happen more often, since the electron is excited for less time in each absorption. I think the classical treatment is easier to understand. Higher frequencies interact more strongly.

Doesn't motion relative to the CMB change its measured temperature, dependent on the angle of viewing?

Excited states imply a bound system, which are the ones with quantized energy levels — you need a negative potential energy (classically speaking) larger in magnitude than KE, which comes from an attractive force. A free electron can only have kinetic energy, and there's no place to "store it until later."

I'm not sure if I entirely agree with the Wikipedia author's suggestion, since there's the possibility that in a configuration where there is an appreciable Casimir force you could decrease one or both of the terms (i.e. c changes) — what implications are there from that? Though I suppose you can argue that it's the magnetic and electric properties of the material and not space that you'd be measuring. But there's the idea that you can't measure something that is a vacuum property because you need to have some sort of probe there, which is decidedly non-vacuum. The actual values are by convention; you could choose them to be 1 in an appropriate coordinate system, but that means other constants would have to change. By choosing certain other constants (e.g. c), the permeability and permittivity have the values that they do.