General Physics Thread

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Random question.

How much faster do objects move in vacuum, compared to environment of regular air pressure and temperature?

I guess it might depend on the type of objects; I'm guessing that the objects that are not affected by air resistance don't get that much faster in vacuum?

How about bullets? Let's assume that the bullet is fired into vacuum. How faster does it get?

Depends upon the object. The ratio between the speed of light in matter versus the one in vacuum is the Refractive index of said material, so there is that.

Arhk, equations! My mortal enemy...

edited 18th Sep '14 11:35:09 AM by dRoy

Oh oh! Mythbusters did a thingy on this.

They were testing whether or a not a gun could fire at all in a vacuum. Spoilers: It totally can.

Anyway, they fired it in this big bulletproof vacuum box and found out that without air slowing the bullet down it traveled an entire 3% faster.

Uh...how much difference does it make? I'm not sure about ballistics.

Say, what about an athletic person? Would s/he be able to run faster in vacuum (assuming that s/he has ground to step on)?

Not a lot. Like it's completely unnoticeable.

And for that I have no idea

Ah, I see.

I'd have to imagine that although something small like a bullet doesn't benefit much from no air resistance. Seeing as it's relatively tiny and pretty aerodynamic. Something big would benefit a lot more.

Like take cars for example. Look at massive increase in performance, weight decrease, aerodynamics and the like between the Bugatti Veyron and the Super Sport. All that extra work just to go a few more miles an hour faster and push against that air.

The main upside to space is that you could make a ship shaped like a brick and it would move just fine.

Nuclear spins control current in plastic LED: Step toward quantum computing, spintronic memory, better displays

Physical constant is constant even in strong gravitational fields

Interesting, but the equivalence principle that General Relativity is about is not quite understood as what the article paints it as being. Equivalence simply means "inertial mass = gravitational mass".

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A nanosized hydrogen generator

Uh, okay. I have teleporters in the book, I'm writing...aaaaand you can probably already see the problem. Infinite energy. While it does require a lot of magic + electricity to power it, there's nothing stopping it from eventually being self sustaining. I was thinking about simply having an object lose all its energy when it passes through, but that has another slew of problems. Basically, I want a way for an object to retain momentum, still be effected by gravity, etc., but a reason why it won't produce infinite power.

I hope I posted it in the right section...

Well, a teleporting device is not going to create infinite power. Assuming that it works like a wormhole, it's merely a shortcut.

What I mean is, the teleporters are portable devices that can be moved anywhere. I want a reason why they can't just put one above the other, stick a generator between them and toss something down.

Ah, that is a complicated concept from General Relativity. Basically, the "gravitational potential" (the energy something has at a given place in a gravitational field; the difference between the potential in point A and the potential in point B is the energy that is required to lift an object from A to B, or the one which is released when an object gets from B to a) is a pathway-independent quantity; thusly, if, say, you let a rock fall from 6km of altitude to the sea level, teleporting the rock back up is gonna take the same amount of energy as if you were carrying it without a teleporter.

Or in plain words; the teleporter only affects the travel time, not the work required/released when travelling the path.

Does this mean that, no matter how many generators are put there or how far apart they are, they'll never gain enough energy back? That would solve a LOT of problems.

What are these generators creating? Energy to push something farther up a gravity well?

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