144 replies to this topic

[Dauth]

It does seem my exams prevented me doing much with this thread, does anyone have a specific question?

[Shirou]

I do, actually. It has to do with physics. With the law that states the preservance of energy.

In the normal water cycle, the sun evaporates water from the ocean. This damp rises up high in the air and, in the form of clouds, gets over land. There, it condenses and falls down. Now the warmth/cold cycle here with damp and liquid water is not what interests me. But the physics of potential energy is. When something is lifted in the air, it gains potential energy, I have learned. Then if it falls down again, it loses that energy.

In hydrogen powered energy stations, we use this potential energy to power turbines and generate electricity. After all, it is the falling of the water, and thus the loss of the energy from the water, that gets the turbines spinning, not? But my question is. Those power stations generate tremendous amounts (to our standards) of energy. But what if the river wasn't interrupted like that and it just flows, where do all those megawatts of potential energy go? Is it really warmth? Does that really mean that a waterfall is actually a giant pool of warmth. I can't get to it, or I just don't understand the physics of potential energy.

[Dauth]

It is all going into the energy of the pool, actually this was the source of the unit of energy, from the Joule experiment

Heat - Calculation below

Sound - Have you heard a waterfall

Momentum - The splash carries momentum and energy away, as does breaking up the rocks at the bottom.

Now for the sake of argument, 1kg of water falls from 10m above into a pool containing 1 cubic metre of water (tiny by the standards of plunge pools). 1 cubic metre = 1000kg

Energy lost by falling water = 9.81*10*1 (mgh) = 98.1J

Energy of pool before = 135.6 million joules (Basic formula for a gas, yes not a perfect model but sufficient to show my point)

Percentage added to the pool energy is 2.24^-4% and even if this continues yes it would heat up the pool but the water is constantly flowing away taking away the new heat etc.

Hope this is sufficient.

[Shirou]

The fact that one cbic metre of water has such amounts of energy inside, rather makes the energy output of a hydro-electric power station, not all that much anymore. I understand now.

[Dauth]

Well, yea but a lot of that is thermal energy which we can't extract due to the second law of thermodynamics. How can you pull heat from something that is colder than the body you're pulling the heat to?

[Shirou]

I know we simply can't

Ok, for the sake of keeping you busy , I have a next question. It's a hard one, I think, as my own physics teacher knew no real answer.

Light acts like a continuous stream of fotons, but also as a wave-effect. I know that in micro terms, its a stream of fotons, and on macro terms, that stream acts like a wave, like water atoms offshore being normally just alone, but all together they form the waves.

But, my teacher is always talking about Light as a wave-effect. And all I have learned about light is that it is always a wave. Even when I see drawings of gamma-radiation to the scale of one radioactive atom (where there is only one foton) it is still pictured as a wave.

If that's so, then why are we talking about light as wave effect so specifically. What is this other side of light, not acting as a wave?

[Dauth]

Bah, today I walked out of a lecture course I didn't want to take that would give a very good solution.

I kinda need to know your level of physics but I am going to assume 1st year degree (hopefully not to high level).

The individual particle of light is indeed the photon, there is a duality called the wave-particle duality, where it is possible for a particle (such as the electron or even something with structure like a proton) to behave as a wave. This is because at the quantum level (and for once the word is used correctly), the concept of a particle breaks down. Now as I imagine it a hydrogen atom in an excited state is a nucleus at 10^-15m (for current intents an purposes a singularity) with and electron wavefunction orbiting around it. The excited state has a shape which I won't go into, however it is possible for this state to decay to the ground state and emit a photon.

This single photon emitted is a particle, it has Spin 1 and a number of other properties. However this particle can (and does) behave as a wave with Energy = frequency * wavelength.

The reason we know it is a particle and not just a wave is that we can identify single photons in devices called Photo multiplier tubes, and before these were invented it fitted the theory.

If you have more questions I can go into virtual pair production but this may be an advanced route not suited to answer the query.

[Dauth]

My next topic will be type 1a supernovae as standard candles (used in cosmology) unless we have something else more relevant.

[Jok3r]

I have a bit of a question... well, more of a theory, but here it is-
Could, theoretically, a nuclear detonation transport an object forward in time?
According to Relativity, nothing can go faster than light because as you near the speed of light, you need more mass to speed up, which slows you down, so you add more mass, slow down... etc. However, if you cant go faster than light, can light go faster than it currently does? Would the tremendous amount of energy created by a thermonuclear warhead cause this? Sorry if I sound like an idiot with no idea what I'm talking about, because I have little grounding in physics, but I thought of this the other day, and don't know anyone with the degree of knowledge required to answer this, so I decided to ask here.
~SLG

[Dauth]

Ok simple explanation first.

Everything travels in time at 1 second per second (in the same inertial frame of reference)

Your description of special relativity (SR) is butchered but correct enough.

However you miss one of the rules of SR, a photon (particle of light) has only one speed (in free space) and that is c, the speed of light. If you sit on a photon moving at c and emit a photon directly infront it will move at c away from you. However in the lab frame someone would see the new photon moving at c aswell.

A thermo-nuclear warhead is a tiny amount of energy, seriously the sun (a tiny star) can't break relativity, so a nuke never will.

There is an explanation in General Relativity (GR) but I really don't think its appropriate for anyone who hasn't at least got a BSc in physics first.

[Sic]

Nice stuff Dauth, you really make physics more enjoyable (even though I like it a lot).

And as for chem questions , meet me after 5 years .
I know some stuff but not much.

[Dauth]

I can answer plenty of chem, failing that Chyros will be the man for the job.

I'm glad people are liking physics because of this.

[Jok3r]

Ahh... that would explain that... however, is there evidence that the sun, a relatively small star, doesn't break relativity when you get close enough to it? or that this hasn't happened before? Just wondering, not to doubt you
~SLG

[Dauth]

Special relativity doesn't work in an intense gravitational field (well any, but the effect from the Earth is to tiny to notice), GR takes over but that is really complex.

[Shirou]

Hah well I have always heard talks about that Gravity is one hell of a mindbreaker, and it's also a big factor in creating the gap between two different theories, being General Relativity and Quantum Theory. Wasn't it quantum theory that couldn't explain Gravity, but can explain everything else?

Oh and I don't have a degree on physics at all as I'm still in middle school (which I'm debt to be until I'm 19, as I have to double one year). I do understand your explanation on my last question. Yet this:

Quote

This is because at the quantum level, the concept of a particle breaks down.

Kind of indicates that these things are a bit above me. I don't even think it's possible to explain why to a simple man like me

Edited by Aftershock, 10 February 2008 - 14:24.

[Dauth]

Quantum theory and GR approach from opposite sides of the problem, QM from the very small and GR from the very large, getting them to meet was always a problem. New theories such as Quantum Gravitation mimic GR on large scales but behave as QM at small scales. This being said it is a research area, above my level, and really designed for Phd students.

Ok bumping this incase people want to ask me anything (since I got my exam results I apparently know more about General Relativity than I thought).

Edited by Dauth, 28 February 2008 - 18:57.

[̀̀̀̀█]

Nice topic here dauth.. I am a theorist myself, natural born to question everyhting around me. I am very very smart when it comes to figureing stuff out, given 5 minutes I can come up with some reasonable answer to just about anything. (pertaining to physics and chemistry)

Any quantum mechanics under your belt? I would think so raeding the topic thus far, but I want to make sure.

I am very into fusion and quantum based energy production, it fascinates me to no end.
So far I have just a few personal questions......

What do you thing of the LHC? (large hardon collider... It is said to make black holes)
I for one think that it is the mayan death date that is in 2012..... But the world won't end, it will jsut cahnge it forever.


Ah, an actual question.

Using Electro magnetic accelerators with the polarization exchange trick, do you think that fusion will be feasible with spirals in a sphere? I think that if we can get the right spin on the atoms they will hit each other in such a way that will easily break the nuclear bonds...... I have yet to get hard math on this, but hey, I am just out of HS you know.


Also, whoever was wondering about thermite, it is fun stuff, and I have made a FAB out of it, a pressure cooker and a bunch of gasoline...... Its funny. I used it to clear half an acre of land for a driveway back in Arizona.

Anyone for the more destructive side of physics, feel free to pop a question my way I will share whatever knowledge I have.

[Dauth]

pyrobob, on 14 Apr 2008, 6:59, said:

Nice topic here dauth.. I am a theorist myself, natural born to question everyhting around me. I am very very smart when it comes to figureing stuff out, given 5 minutes I can come up with some reasonable answer to just about anything. (pertaining to physics and chemistry)

Any quantum mechanics under your belt? I would think so raeding the topic thus far, but I want to make sure.

Theorist, means someone who has made a theory, I am a theoretician, since I study theories.
I have studied a lot of QM, but have not studied relativistic QM

Quote

I am very into fusion and quantum based energy production, it fascinates me to no end.
So far I have just a few personal questions......

What do you thing of the LHC? (large hardon collider... It is said to make black holes)
I for one think that it is the mayan death date that is in 2012..... But the world won't end, it will jsut cahnge it forever.

Check out the OMG-particle on wikipedia, it has more energy than the LHC and hasn't killed the Earth yet.

Quote

(large hardon collider... It is said to make black holes)

it's not a hardon collider, it's a hadron collider

Quote

Ah, an actual question.

Using Electro magnetic accelerators with the polarization exchange trick, do you think that fusion will be feasible with spirals in a sphere? I think that if we can get the right spin on the atoms they will hit each other in such a way that will easily break the nuclear bonds...... I have yet to get hard math on this, but hey, I am just out of HS you know.

Fusion held by magnetic confinement (EM) is probably our best method of fusion, one experimental reactor has had a few seconds of power production so it looks likely.

Quote

Also, whoever was wondering about thermite, it is fun stuff, and I have made a FAB out of it, a pressure cooker and a bunch of gasoline...... Its funny. I used it to clear half an acre of land for a driveway back in Arizona.

Anyone for the more destructive side of physics, feel free to pop a question my way I will share whatever knowledge I have.

That's more chemistry than physics, but it's still a nice clearing method.

[̀̀̀̀█]

HARDON COLLIDER! Its a joke, I know its a hadron....... Knew you would pick that up >.<

[Dr. Strangelove]

Bah, I had a question for Dauth but I went and answered it myself.

EDIT: I have a new question, and it should be a ton simpler than the one I just answered for myself, which was about wave functions collapsing for quarks, the question is:

How do magnets affect things at a distance?

Edited by J.R. Bob Dobbs, 14 April 2008 - 09:15.

[Crazykenny]

Are Radiation-Free Nuclear weapons possible? Or at least Nuclear weapons of which the radiation life-span is much shorter.

Edited by Crazykenny, 14 April 2008 - 14:17.

[Dauth]

J.R. Bob Dobbs, on 14 Apr 2008, 9:58, said:

Bah, I had a question for Dauth but I went and answered it myself.

EDIT: I have a new question, and it should be a ton simpler than the one I just answered for myself, which was about wave functions collapsing for quarks, the question is:

How do magnets affect things at a distance?

I hate EM, with a passion that can only be described as strong, it also depends on the source of the field.

Accelerating fields are proportional to 1/r
Moving fields are 1/(r^2)
And IIRC static fields are 1/(r^3)

Otherwise they work the same was as at a short distance, but with the effect greatly reduced.

Crazykenny, on 14 Apr 2008, 15:16, said:

Are Radiation-Free Nuclear weapons possible? Or at least Nuclear weapons of which the radiation life-span is much shorter.

1st, not really since breaking into any nucleus generates radiation
2nd, yea, they are neutron bombs, flood an area with neutrons it will wipe out all life, neutrons have a half life of 15min, then it decays to hydrogen atom + electron anti neutrino, within 24 hours it's safe and the hydrogen is in the upper atmosphere so no danger of exploding.

[Crazykenny]

And what about the Co-bomb, or Salted Bomb. How do there atoms work? Because they have a far longer life-span, but still remain strong enough to kill life.

[Dauth]

Tbh study of specific isotopes is practically Chemistry, you need a short lifespan something that you can get at least 100 lifetimes in before the humans arrive.

[Crazykenny]

Cobalt-60