An Introduction to Zero-Point Energy

CalPhysics.org ^

[inquest]

I've never heard that Terra, Luna, and Sol are any more "proper" than earth, moon, and sun. The words mean the exact same thing, just in different languages.

[PatrickHenry]

I've never heard that Terra, Luna, and Sol are any more "proper" than earth, moon, and sun. The words mean the exact same thing, just in different languages.

Depends on context. If a hole is being dug in the earth (refering only to the ground), I wouldn't capitalize it. If I'm refering to the orbit of the Earth (name of the planet), I would. But I'm not the final authority in such matters. Your editor will enforce his own rules.

[Semper911]

Earth: It is lowercase unless at the beginning of a sentence. ... depending on whether your English teacher insists.

I very much doubt an English teacher would insist that you use lower case for Jupiter, Saturn, or Mars. Likewise Earth.

When we say "the earth", we are really saying "the planet named Earth."

It is a minor point, though, and my proofreading correction really didn't belong on this physics thread. (But as we all know, there is no slack on FR.)

[TheJollyRoger]

It's the same at all points...so it cannot be measured...
but it can be an energy source???

Crap Crap Crap Crap Crap Crap Crap Crap Crap Crap Crap

[sourcery]

It's the same at all points...so it cannot be measured... but it can be an energy source???

That would appear to be the crux of the issue. I haven't heard a good explanation regarding how one gets usable energy from ZPE without violation of the thermodynamics/conservation laws. But some rather smart people seem to think there may be a way, so I'll be willing to listen to any explanation that might be forthcoming from a credible source.

[Jason_b]

I wish I found this thread earlier, but I was out to dinner.

Car wheels against the road: all that is happening is mechanical energy is being released in a way that moves the car forward. Wheel to road is just another example of clutch to flywheel or gear to gear, or gear to driveshaft.
The energy comes from chemical potential energy in the liquid hydrocarbon fuel being combusted and converted into heat and gas which pushes the piston.

With your foot and the ground, that is also merely transmission, the energy comes from metabolism and the processing of sugars.

The key point was said in an earlier post referencing Newton's law, "III. For every action there is an equal and opposite reaction." If you were floating free in space and had a bowling ball in your hand, and you threw it away with vigor, the ball would be set in straight line motion away from you, but you would be moving away from the point of release as well, in a straight line and in the opposite direction. You will have propelled yourself. And you would continue on in that line and the ball opposite forever until some force acted to stop you or change your directions.

Now take an amount of gas the total mass of which is equal to the ball, compress it, and release it suddenly while floating in space. You acceleration however brief, a better word would be impulse, would be the same as if you had thrown the ball. A rocket engine produces thrust that is as if you had a limitless supply of those impulses (until the fuel runs out) laid them end to end so there is no beginning or end, just a stream.

[VadeRetro]

That would be my first impression. But I am humble, and am always willing to consider the possibility that I am wrong.

But what are the odds that both of us are wrong?

[cinFLA]

On Earth there is always air or water available to push against.

I enjoyed your explanation but I still have an argument with the statement above (not yours). It implies the force is derived from "pushing" against the air which is a popular misconception and totally ignores the fact that the air or water is accelerated by the propellor.

[cinFLA]

If it said "push the air" I would have less disagreement but it says "push against". How is the heck can the road push the car???????

[cinFLA]

Physicists, like engingeers don't always have the best writing skills.

But they are usually technically accurate and do not write in the jargon of the uniformed layman.

[sourcery]

On Earth there is always air or water available to push against.

Ah. I see. I interpreted that statement as simply referring to the fact that the propellor blades transfer momentum to molecules of air by hitting them, although I admit that "push" is probably not the best verb to describe the process.

[PatrickHenry]

Placemarker.

[sourcery]

But what are the odds that both of us are wrong?

OddsWrong(VadeRetro, Sourcery) = OddsWrong(VadeRetro) * OddsWrong(sourcery)

[cinFLA]

The propellor is also an airfoil. The "faster" airstream on the front side produces significant lift.

[djr]

What's your take on:

"When a passenger in an airplane feels pushed against his seat as the airplane accelerates down the runway, or when a driver feels pushed to the left when her car makes a sharp turn to the right, what is doing the pushing? Since the time of Newton, this has been attributed to an innate property of matter called inertia."

When being accelerated, we are pushed in the direction of acceleration and that's what we physically "feel". Now there may be some interesting mysteries beneath all this, as the article suggests, but in this set of examples it seems like an effort is being made to mystify scenarios that are completely consistent with basic explanations.

[cinFLA]

You acceleration however brief, a better word would be impulse, would be the same as if you had thrown the ball.

Only if the total momemtum of each is equal. Your acceleration would depend in one case on the amount of pressure and in the other on how hard you threw the ball.

[cinFLA]

but in this set of examples it seems like an effort is being made to mystify scenarios that are completely consistent with basic explanations.

Classical physics is fine for modeling our everyday life. However, as we learn more we must refine our models. For example, light was once modeled as only a wave. Now it is modeled as a wave and a particle. My grad school is almost 30 years ago so maybe someone else can update. Similarly, gravity is modeled as a wave? particle? other? Go figure. Time for a cool one.

[cinFLA]

I'm afraid I don't understand what you're driving at, either. Could you spell it out for us?

A common misconception by laymen is that the force is derived from "pushing against" the water/air as in pushing against a wall. In reality, the force is derived from the acceleration of the water/air. The force would be the same in a vacuum for the same amount of water/air accelerated even though there would be no air/water to push against.

[js1138]

But what are the odds that both of us are wrong?

Without even reading the propositions, I'd bet higher than both of you being right. ;^)

[RightWhale]

lower case for Jupiter, Saturn, or Mars

This is far more interesting and useful than ZPE. Jupiter, Saturn, Mars, Venus, Sol, Luna, Terra, Pluto are classical, formal, proper names for the planets and are capitalized. Informal terms such as earth, moon, and sun are common names and are not capitalized. But as another poster mentioned, your editor will make the final decision.