General Physics Questions

mcbethcg · Jul 17, 2004

The purpose of this thread is for people to ask physics questions and get possible answers from others. I'll start it off. Q. Neutron stars are made of neutrons that are squeezed together to form a very dense material. Since neutrons have no charge, and should neither repell or attract other neutrons, is there any reason why neutrons could not be artificially collected closely together? Capture them somehow and put put them in a jar?

nacnud · Jul 17, 2004

Because they arn't stable, a free nutron only has a half life of 15 minutes. Since neutrons have no charge, and should neither repell or attract other neutrons but they are still governed by the strong nuclear force [wikipedia]

Saiph · Jul 17, 2004

and the pauli exclusion principle. But yeah, the decay time's the killer here. Only in strong bonding situations, like an atomic nucleus, or the intense pressures of a neutron star, do they continue to exist for long periods of time. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

the_id · Jul 18, 2004

Ok, here's a physics question. I think I already know the answer but would appreciate anyone else's input. An object with mass begins to accelerate. The closer it gets to the speed of light, the more its mass increases. Is it possible then that such an object's mass would become such that it exerted a gravitational influence on the rest of the universe - the same way a planet does? If so, would not such an object passing over the asteroid belt and traveling at say 0.999 c tend to "suck" some of those asteroids out of their solar orbits? (provided of course it passed close enough to said asteroids)

mcbethcg · Jul 18, 2004

Yes, the mass of the object would excert gravitational influence, even if it were derived from relativistic velocity. Of course, the amount of energy required to accelerate a mass to gain 1 pound of mass equals the energy obtained by totally annihilating 1 pound of mass and converting it to kinetic energy.

the_id · Jul 18, 2004

So in other words, my Volkswagen’s probably not gonna cut it, huh?

Saiph · Jul 18, 2004

actually, the "mass" increase is a misnomer. The inertia of an object, that is the objects resistance to a change in velocity (to acceleratioN) increases. Normally, this is what mass measures. However, the "mass" increase due to velocity does not exert gravitational forces, only an objects "rest mass" does. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

the_id · Jul 18, 2004

If I’m understanding you, even something traveling very close to c would exert no more gravitational influence than if it were at rest.

mcbethcg · Jul 18, 2004

I stand corrected.

Saiph · Jul 18, 2004

basically by using relativistic "mass" only confusion results, since it's a loaded word. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nissasa · Jul 18, 2004

I heard somewhere that an objects velocity cannot be determined in space without a reference point. Wouldn't the increase in energy requirement due to relativistic mass be measured and tell you what your "speed" is? Or was that just a myth I heard?

mcbethcg · Jul 18, 2004

Because there needs to be something to keep us from exceeding the speed limit.

mcbethcg · Jul 18, 2004

Quantum physics question for those of you in the know. Wave forms collapse when "observed". What constitutes "observed"? Is it possible to build a device that senses whether or not a wave form has collapsed and does something as a result, as a method for detecting whether the experiment is being observed from a distance? Ie: you have a black box that has an internal two-slit experiment, with some tiny window for external observation to collapse or not collapse the wave form. It sounds a buzzer if observation occurs.

nacnud · Jul 18, 2004

An observation is any event that interacts with the wave form directly, ie the screen of your two slit experiment. It does not mean a human observation.

mcbethcg · Jul 18, 2004

I think you are wrong there. Read many articles on the two slit experiment. Observation occurs when particles are detected going through one slit or the other. Knowing which slit the particles go through is an observation. The screen is where the interferance patern exists.

nacnud · Jul 18, 2004

Well you are observing the particle at the slit instead then which will destroy the wave function. Here is a good overview of the ideas behind the experiment. Sorry to answer in links but the explanation given there is much better than I would give and is more detailed.

scottcarlin · Jul 18, 2004

Q. For the electricity that is applied to our homes(United States), does the voltage alternate between 120 and 0 volts or 120 and -120 volts?

the_id · Jul 19, 2004

Actually, 240 volts is what is delivered to most residential meters in the U. S. There it's split into 2 lines, each carrying 120 volts. And unless there's a problem, the current at any normal receptacle should not be dropping below around 105.

Saiph · Jul 19, 2004

nissasa: Nope, don't work. different people measuring different speeds (depending on their frame of reference) will measure different inertia increases. It's sorta like, a man throws a baseball at you, going 50mph, you catch it. Now, imagine you're in a truck, receeding at 45 mph. You're going to measure the ball going 5 mph, and it's going to feel that way when you catch it. Or, you can turn it around for when you throw it. In your frame it takes so much energy to get the ball going 50mph. Doesn't matter how fast you're going, you'll always measure the same. Now, someone standing "still" on the roadside is going to see it, plus the speed from the truck, that's where the extra energy comes in. Or say they're moving, the extra energy in their motion is what they see in addition to the 50mph worth you threw it. Reltivity says there's no difference between the last two statements either, since velocity depends on the reference frame. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Jul 19, 2004

nacund has the wave collapse right. It's basically whenever there is an interaction that determines the object to be in a specific state. Normally, as a wave, the particle has only a probability of being in certain states, called eigenstates. Before you observe/interact with it, you can only guess, based on probability, which state its going to be in. However, once you look, once you interact, and figure out which energy level it is in (by a detector, or say a molecule binds with it or whatever, and interaction measuring/requiring a specific state) that's the one it's in. If you look again, it'll be in the same one. From that point on, assuming nothing changes (which given time will happen) it'll be in that state again, and again. It's no longer probalistic. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

Saiph · Jul 19, 2004

good question scott. The current is alternating (notice I said current, not voltage), and so shifts from going one way to another. Depending on the device, this is a good thing. If it isn't, you'll see a DC converter in the circuit somewhere (often the big "box" part of a plug that isn't just two prongs, or buried in the device). As for voltage, it too oscillates. It does go from positive to negative, but it actually goes from +170 to -170. The reason it's usually refered to as a 120 or 110 v outlet is that'the average voltage. It doesn't spend much time at 170, and even less at 0 (the voltage drops rapidly through that point) giving us a 120 v average. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

scottcarlin · Jul 19, 2004

So if the current is going back and forth then how does it get to our houses, it seems like the electrons/holes would be boing back and forth and not getting anywhere.

blairf · Jul 19, 2004

"it seems like the electrons/holes would be boing back and forth and not getting anywhere" Which is a good thing really! What would you do with all those pesky electrons coming out of your socket, and the poor electricity company would need to keep pumping electrons in at the other end. For a 5A current in a typical wire the elctron drift velocity is only a tenth a millimeter per second. Don't confuse the "speed" of the current and the "speed" of the electrons.

scottcarlin · Jul 19, 2004

"What would you do with all those pesky electrons coming out of your socket, and the poor electricity company would need to keep pumping electrons in at the other end. " That couldn't happen anyways, when you plug something in to a socket it completes the circuit and only then will the current start flowing. "Don't confuse the "speed" of the current and the "speed" of the electrons." I'm not confused about that. I'm confused about the fact that the since the voltage is oscillating between a positive and negative value, how is the current allowed to flow. Ok....If you were to take a scope to each hole on your wall socket, what would each one read?

mcbethcg · Jul 19, 2004

But what about schoedingers cat?

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