For Questions That Don't Merit Their Own Thread

[Grand Ship Builder]

If we somehow got a nearly frictionless coating in a hole where an axle is, put a wheel with holes on it, added objects in those holes that have enough weight to move the wheel down, and put it in a vacuum, could we create a perpetual motion machine? Gravity would pull the objects down, forcing the wheel to spin, and with no friction or air resistance to stop it, the wheel could spin forever, and then we could attach a generator to it, for infinite free energy. Would that work?

[Racescort666]

9 minutes ago, Grand Ship Builder said:

nearly frictionless

No.

Also, you're exchanging potential energy (objects in a gravitational field) for kinetic energy (wheel turning). As the weights go back around the wheel they gain their potential energy back in exchange for kinetic energy slowing the wheel back down. Basically, you've made a pendulum. If you attach a generator to it, you are converting kinetic energy into potential energy (electric this time) and the wheel slows down. 

Electric power generation works by converting energy from one state to another. There are always losses from thermodynamics or friction or whatever so perpetual motion devices can't exist. 

There are things that are practically unlimited like using Jupiter for a gravity assist. You trade some of Jupiter's orbital energy to your spacecraft. The spacecraft gets a speed boost but Jupiter's speed barely changes because it's 24 orders of magnitude more massive.

[0111narwhalz]

1 hour ago, Grand Ship Builder said:

infinite free energy

Refer to the law of conservation of energy.

[DerekL1963]

2 hours ago, Grand Ship Builder said:

Gravity would pull the objects down, forcing the wheel to spin

Gravity would pull on objects on both sides of the wheel equally.  Those objects on one side would try to turn it clockwise.  Those on the other, counterclockwise.  Net motion - zero.   If it were unbalanced, the energy added by gravitational attraction as the heavy side rotated downwards would be subtracted by gravitational attraction as the heavy side rotated upwards.    Even in a vacuum, with a totally frictionless bearing, it would be nothing but a pendulum.

[Grand Ship Builder]

1 minute ago, DerekL1963 said:

Gravity would pull on objects on both sides of the wheel equally.  Those objects on one side would try to turn it clockwise.  Those on the other, counterclockwise.  Net motion - zero.   If it were unbalanced, the energy added by gravitational attraction as the heavy side rotated downwards would be subtracted by gravitational attraction as the heavy side rotated upwards.    Even in a vacuum, with a totally frictionless bearing, it would be nothing but a pendulum.

I was referring to something similar to this:

Spoiler

 

 

Anyways, what would happen if a blackhole the mass of the earth went straight through the Sun at escape velocity?

[DerekL1963]

1 minute ago, Grand Ship Builder said:

I was referring to something similar to this:

Same answer.  Friction just makes it stop faster.  Taking energy out of the system by hooking it to a generator... faster still.

[Grand Ship Builder]

12 hours ago, Grand Ship Builder said:

Anyways, what would happen if a blackhole the mass of the earth went straight through the Sun at escape velocity?

 Now this question please.

Edited October 24, 2017 by Grand Ship Builder

[Kerbinchaser]

42 minutes ago, Grand Ship Builder said:

 

Anyways, what would happen if a blackhole the mass of the earth went straight through the Sun at escape velocity?

Spoiler

It would be that. 

 

Edited October 23, 2017 by Lo Var Lachland

[Grand Ship Builder]

52 minutes ago, Lo Var Lachland said:

  Hide contents

It would be that. 

 

Edited October 24, 2017 by Grand Ship Builder

[peadar1987]

10 hours ago, Grand Ship Builder said:

 Now this question.

Now this question please.

So a black hole of earth's mass would have a radius of 9mm and a mass of 6*10²⁴kg.  Solar escape velocity is 617km/s and the diameter of the sun is 1.4 million km, which means the black hole will pass through the sun in a time of about 35 minutes. Something that mass with that small of an area isn't going to experience any significant change in velocity due to drag.

The tube of matter that the black hole would directly pass through (and therefore absorb) would have a mass of 5*10⁸kg ((pi *9mm²) * 1.4 million km * the density of the sun), which wouldn't cause a significant increase in its mass.

Matter falling into a black hole can release up to 40% of its mass-energy in the form of some pretty hard radiation. By E=m*c² this gives a total energy release of 2*10²⁵ Joules. Spread over the 35 minutes it takes for the black hole to pass through the sun, this gives an average power of 9.5*10²¹ Watts. When you're directly converting mass into energy, the effects of momentum and velocity changes are going to be pretty negligible, so we can safely assume that this is pretty much the total energy released.

The sun's normal power output is about 3.85*10²⁶ Watts, so the effect of the black hole hitting the sun would result in its output brightening by about a thousandth of 1%. So actually we probably wouldn't even notice.

**Edit: The black hole would actually take less than 35 minutes to pass through the sun, as it will still be accelerating after it goes past the surface (I am too lazy to do the integral). However, we could reduce the time by several orders of magnitude and the net effect on the power output of the sun would still be negligible.

Edited October 24, 2017 by peadar1987
maths

[p1t1o]

3 hours ago, peadar1987 said:

Now this question please.

So a black hole of earth's mass would have a radius of 9mm and a mass of 6*10²⁴kg.  Solar escape velocity is 617km/s and the diameter of the sun is 1.4 million km, which means the black hole will pass through the sun in a time of about 35 minutes. Something that mass with that small of an area isn't going to experience any significant change in velocity due to drag.

The tube of matter that the black hole would directly pass through (and therefore absorb) would have a mass of 5*10⁸kg ((pi *9mm²) * 1.4 million km * the density of the sun), which wouldn't cause a significant increase in its mass.

Matter falling into a black hole can release up to 40% of its mass-energy in the form of some pretty hard radiation. By E=m*c² this gives a total energy release of 2*10²⁵ Joules. Spread over the 35 minutes it takes for the black hole to pass through the sun, this gives an average power of 9.5*10²¹ Watts. When you're directly converting mass into energy, the effects of momentum and velocity changes are going to be pretty negligible, so we can safely assume that this is pretty much the total energy released.

The sun's normal power output is about 3.85*10²⁶ Watts, so the effect of the black hole hitting the sun would result in its output brightening by about a thousandth of 1%. So actually we probably wouldn't even notice.

**Edit: The black hole would actually take less than 35 minutes to pass through the sun, as it will still be accelerating after it goes past the surface (I am too lazy to do the integral). However, we could reduce the time by several orders of magnitude and the net effect on the power output of the sun would still be negligible.

Its should be noted that it will influence a column of matter much wider than 9mm, but on the other hand the radius (9mm) will severely restrict the rate of matter in-fall, not least because of the radiation pressure caused by that 40% matter conversion. 

[peadar1987]

22 minutes ago, p1t1o said:

Its should be noted that it will influence a column of matter much wider than 9mm, but on the other hand the radius (9mm) will severely restrict the rate of matter in-fall, not least because of the radiation pressure caused by that 40% matter conversion. 

Yeah, I was going to add a fudge factor to take that into account (although I suspect that with the speed the black hole is moving, matter from outside that column won't have too much chance to actually fall in before the column has passed), but then realised how many orders of magnitude this would be away from any sort of noticeable effect. And I didn't even consider the radiation pressure

[p1t1o]

17 hours ago, peadar1987 said:

 matter from outside that column won't have too much chance to actually fall in 

Debatable, it may only have Earth's mass, but at 9mm radius, the force of gravity will be quite severe.

Quick calculation show that the force between it and 1g of hydrogen at a distance of 1cm will be 4e15 newtons.

VERY rough calc shows this is sufficient to move it (the 1g H2) 2km in the 0.1 microseconds or so it takes the hole to move 10cm.

So it can at least be shown that the influence radius diameter is >9mm, how far it practically extends is anyones guess.

**edit**

I think im a couple of factors of ten out, or more likely the calculator I used was not suitable for relativistic situations, since 2km in 0.1us is somthing like 60c...

I think the conclusion is unchanged.

Edited October 25, 2017 by p1t1o

[spacebrick3]

Here's a question I had about the Doppler effect:

So, galaxies that are near the edge of our visible universe (~12 billion light-years distant) are moving away from us extremely fast and thus are extremely redshifted, so the peak wavelength that we see is significantly longer than it would be otherwise. So my question is, when we look at these galaxies in the visible spectrum, are we actually seeing them in the ultraviolet? Is it redshifted enough that the ultraviolet is stretched to the length of visible light?

[James Kerman]

On ‎19‎/‎10‎/‎2017 at 9:52 PM, Toonu said:

I saw fire extinguisher, which extinguish the fire by sound a long time ago. Have anyone any news on it? If development is still ongoing or not?

Two engineering students from George Mason University have invented a new fire extinguisher, capable of putting out flames by manipulating sound waves.

https://www.engineersaustralia.org.au/portal/news/sonic-fire-extinguisher-puts-out-flames-sound

[Toonu]

4 hours ago, James Kerman said:

Two engineering students from George Mason University have invented a new fire extinguisher, capable of putting out flames by manipulating sound waves.

https://www.engineersaustralia.org.au/portal/news/sonic-fire-extinguisher-puts-out-flames-sound

Thanks, at least its moving somewhere into more usable machine in future.

[Green Baron]

People in Skyrim cry out the fire with collective "1-1-2" cries ...

[tater]

 

[Vanamonde]

Please save the joke-type posts for less serious threads. This sub is for actual science discussions. 

[adsii1970]

9 hours ago, Toonu said:

Thanks, at least its moving somewhere into more usable machine in future.

And that's not the only thing intense sound is for...

http://www.npr.org/templates/story/story.php?storyId=4857417

[p1t1o]

15 hours ago, spacebrick3 said:

Here's a question I had about the Doppler effect:

So, galaxies that are near the edge of our visible universe (~12 billion light-years distant) are moving away from us extremely fast and thus are extremely redshifted, so the peak wavelength that we see is significantly longer than it would be otherwise. So my question is, when we look at these galaxies in the visible spectrum, are we actually seeing them in the ultraviolet? Is it redshifted enough that the ultraviolet is stretched to the length of visible light?

It can easily be more pronounced than that, at the highest observable levels of redshift, soft X-rays can be shifted into the visible, UV will be right down in the radio spectrum.

 

[Grand Ship Builder]

Not a question, but some fun facts about light and shadows that may answer some questions.

1. A electron can move faster than light in water.
2. Photonic booms, sonic booms but with light instead of sound, are possible, and exist.
3. Light has force. It can move things.
4. You technically weigh more under light than in darkness, that the city of Chicago weighs pounds more on a sunny day, and light can move a spacecraft travelling from Earth to Mars 1,000 km off course.
5. The brightest point of a shadow of a circular object is the middle.

Sources and more information:

Spoiler

1:

2:

 

[spacebrick3]

11 hours ago, p1t1o said:

It can easily be more pronounced than that, at the highest observable levels of redshift, soft X-rays can be shifted into the visible, UV will be right down in the radio spectrum.

 

Wow! I didn't think that it would be shifted that much. Thanks for answering my question!

[p1t1o]

21 hours ago, Grand Ship Builder said:

Not a question, but some fun facts about light and shadows that may answer some questions.

You should totally make a standalone thread for comments like this!!!

For some reason I cant seem to phrase that in a way that doesnt come off as super-sarcastic in text form, but Im not I swear.

[Racescort666]

4 hours ago, p1t1o said:

You should totally make a standalone thread for comments like this!!!

For some reason I cant seem to phrase that in a way that doesnt come off as super-sarcastic in text form, but Im not I swear.

Ultimate answers for ultimate questions, excellent. I’ll start: 42.

I get your point though, a thread for random science facts or something?