Ask a physicist anything. (8)

When astronauts do spacewalks to work on the outside of the ISS, what do they use for lighting? Is there exterior lighting outside the craft, or do they have lights on their helmets as coal miners do? I think that as they orbit they only have about 45 minutes of sunlight followed by 45 minutes of darkness, right? (Personally, I wouldn't mind that work schedule - a 45 minute break after every 45 minutes of work, but not very efficient, eh?)

Chesterton said:

When astronauts do spacewalks to work on the outside of the ISS, what do they use for lighting? Is there exterior lighting outside the craft, or do they have lights on their helmets as coal miners do? I think that as they orbit they only have about 45 minutes of sunlight followed by 45 minutes of darkness, right? (Personally, I wouldn't mind that work schedule - a 45 minute break after every 45 minutes of work, but not very efficient, eh?)

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Spaceflight Now | Breaking News | PHOTOS: Astronauts venture outside for repair spacewalk

Maxwell511 said:

I'm amazed this thread is still going!

Well done Wiccan_Child

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I'm more amazed someone remembers I was the original poster But this has definitely been a group effort, both from physicists (and others) giving great responses, and from inquisitive people asking great questions .

One of the reasons I like this thread is because sometimes I have a stupid question which doesn't really deserve a thread of its own, but I can ask it here and Wiccan or someone else will come back with some kind of interesting reply.

Wiccan Child, I think the "I am a scientist" quote, though used on Stargate SG1, and also used in ST:TNG and at least one Star Trek movie ("Undiscovered Country"?) originates from *either Einstein or Rutherford. I think the later, but I could be wrong (though it is a rarity).

What gives cellophane the magnetic quality it has? I was trying to throw away a piece of thin cellophane wrapping and it kept sticking to my fingers, then it stuck to the side of the trash can.

Chesterton said:

What gives cellophane the magnetic quality it has? I was trying to throw away a piece of thin cellophane wrapping and it kept sticking to my fingers, then it stuck to the side of the trash can.

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In short, static electricity. Like when you rub a balloon with cloth and can then stick it to a wall.

When you peel clingy cellophane off something, that peeling (I'm guessing) is much like the rubbing, which causes a charge separation, so that it has static electricity. Since the cellophane is very light, the effects of the slight charge can be quite strong.

essentialsaltes said:

In short, static electricity. Like when you rub a balloon with cloth and can then stick it to a wall.

When you peel clingy cellophane off something, that peeling (I'm guessing) is much like the rubbing, which causes a charge separation, so that it has static electricity. Since the cellophane is very light, the effects of the slight charge can be quite strong.

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That makes sense.

I'm using a mouse recording program and trying to capture the perfect break in an online game of pool.

I've done it before but since I messed around with my monitor's settings, it no longer works and I have to start all over again.

I thought I would just keep grinding it out until I finally got it right but I'm just not feeling it anymore for some reason.

Instead of getting super lucky, since everything has to be pixel perfect for it to work, I was thinking perhaps I could solve this using number logic.

Here's my best attempt so far and it pockets 5 balls on the break and is really super close to the one I had before which pockets 6 balls.

1. {LMouse down (222,374)}..
2. {LMouse up (133,228)}..
3. {LMouse down (570,358)}..
4. {LMouse up (57,193)}..
5. {LMouse down (57,193)}..
6. {LMouse up (57,193)}..

Here's an explanation of the code:
1. Grabs the cue ball
2. Places the cue ball towards the upper left part of the pool table
3. Aims the pool stick
4. and 5. Moves the pool stick back for power
6. Makes the shot

I'm so close on this. It actually seems like I'm just a pixel off somewhere with either the cue ball placement or the angle on the shot or maybe a little of both.

What I would like is to have all possible permutations for 2. and 3. plus or minus 5 from these numbers.

So for 2. it would be something like {LMouse up (133±5,228±5)}..
and 3. would be something like {LMouse down (570±5,358±5)}..

What is an easy way to generate a complete list for this so I can enter each of them in using a Hex Editor until I hit the right spot?

Hopefully this makes sense to someone.

Okay.

So I just rifled through all possible permutations with {LMouse up (133±5,228±5)} and not even touching the additional {LMouse down (570±5,358±5)} part.

I'm already burnt out.

I don't think this is the way to do it.

I am curious though, what was the total possible combinations on this problem?

I'm thinking that it has to be a much larger number than what I had imagined.

Zippy the Wonderslug said:

Okay.

So I just rifled through all possible permutations with {LMouse up (133±5,228±5)} and not even touching the additional {LMouse down (570±5,358±5)} part.

I'm already burnt out.

I don't think this is the way to do it.

I am curious though, what was the total possible combinations on this problem?

I'm thinking that it has to be a much larger number than what I had imagined.

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If I understood the question, the number of different ways is 11[sup]n[/sup], where n is the number of numbers you're varying. 133±5 has 11 possible values (128 to 138, inclusive), and each of those has 11 more values due to 228±5. Adding the ±5 blurs' that point into a 11x11 grid of points centred on (133,228), hence, 11[sup]2[/sup] possible points to try. If you then start manipulating {LMouseDown}, you have 11 more points per point per variable - i.e., 11[sup]n[/sup].

So {LMouseUp} alone has 121 points, but it you 'blur' all four numbers to try all possible combinations, there will be 11[sup]4[/sup] = 14,641 possible combinations of each number. Which is a lot for a human to do.

I think you got my question.

Every possible separate points on a graph with the following.


Point one being:

(133±5,228±5)

and point two being:

(570±5,358±5)

I'm not about to try all possible 14,641 combinations on this.

Thank you for helping me focus.

For those of you who are wondering why I posted such a weird request here....

I used to be able to clear an entire pool table in 35 seconds and there was no one quite like me in the entire world on that site.



Since I was stupid and changed the settings on my monitor, I'm only looking to try and do this again.

Id be very thankful for an answer to this one.

1]
I am assuming that something like light was emitted at the Big Bang (someone said high energy photons or EMR, gamma rays IIRC), so the universe sould have a "light cone" (be an ever expanding sphere of light), but we have chemical elements all around, not just light, so when did the slow down occurr? I thought that if there was no stuff for the BB light to bump into it would not slow down, according to the laws of physics momentum is constant without outside interference, so we all ought to be made of light somehow I imagine...

2]
Also, is the universe flat somehow, a 3D plus time universe doesnt feel right, I am thinking it ought to be 2D plus time as the light cone (like a shpere surface) expands. That would make the universe slightly curved, but still 3D perception would be a bit of an illusion? I feel as if it might really be a (make up term) "sheet universe", with all the stars and planets really placed on a plane rather than hovering inside a sphere, or a globule, or an "orrery" or something. Am I maybe thinking along the lines of a hollographic world perhaps? This idea is likely to be because I am thinking that a time slice must be really thin, maybe a planck length thin or something, so at any one time the creation is like a superthin slice of bread rather than a big fat loaf.

..the appearance of distant and near, and the apparent age of the distant stars light "travelling" to us through 3d space, would be due to a misconception. There would be the appearance of age evolving on a flat sheet, rather than a real age in a 3d world. Like the whole universe being an evolving colourful projection onto a flat bedsheet, (but without a projector) with different colours representing embedded-apparent age rather than different objects really having emitted light from a network of various 3d locations, like bubbles in a loaf..

http://www.youtube.com/watch?v=1uty0p0-nEU

^^^like this, the universe is the screen, and the disco lights (in 3d) are not really there, they are a misconception.

The colours and patterns on the sheet represent the apparent 3d world, "external 3d objects" really being flat shapes misconceived. The external 3d light show would be a faulty model, the universe is just a sheet.

GrowingSmaller said:

Id be very thankful for an answer to this one.

I am assuming that something like light was emitted at the Big Bang (someone said high energy photons or EMR, gamma rays IIRC), so the universe sould have a "light cone" (be an ever expanding sphere of light)

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The Big Bang did not occur at one point, and then 'spread out' into already existing space.

It looks as though the Big Bang happened everywhere.

When we look backwards in time, the energy density of the universe goes up and up and up towards a singularity.

That energy density is made of a lot of different things, not just light. Just as when we use atom smashers to probe higher and higher energies, all sorts of particles come out, and some of those particles are the everyday kinds of things that make up the ordinary matter we see today.

Also, is the universe flat somehow, a 3D plus time universe doesnt feel right, I am thinking it ought to be 2D plus time as the light cone (like a shpere surface) expands.

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I think the problem is in fully picturing a 4D universe. Most diagrams tend to only show 2D plus time, because it's much easier to picture.

But most assuredly, if you point your left arm forward, your right arm to the right, and the top of your head points up... we live in a 3D universe (plus time).

Am I maybe thinking along the lines of a hollographic world perhaps?

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Very possibly. Some models of physics of our universe are mathematically equivalent to physics on a manifold with one dimension less. And everything occurs in 2D, but 'appears' to be 3D. At this point, I think it becomes very philosophical to argue about whether it is really 2D or 3D. I just use look at my body parts and assure myself I have three dimensions.

Two players alternately roll a die.

The player who fails to improve upon the previous roll loses.

What is the probability that the first player wins?

AV1611VET said:

Two players alternately roll a die.

The player who fails to improve upon the previous roll loses.

What is the probability that the first player wins?

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Worse than 50%, since the first player has the first chance to lose.

AV1611VET said:

Two players alternately roll a die.

The player who fails to improve upon the previous roll loses.

What is the probability that the first player wins?

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Using iterative formulae and a nifty online tool to do partial sums, the odds that the first player wins is about 37% (0.36842105263157904...), while the odds that the second player wins is about 63% (0.631578947368421...).

For those interested, the odds that either player will win in a given round is 15/36 (since there are 36 outcomes per round, 15 of which result in 'win' for the current player), and then it's just a case of mapping out the probability tree, and adding up all infinity of the 'player one wins' scenarios (hence the use of partial sums to find the limit).

You flip a coin, and whatever it lands on, you get a dollar.

Thereafter every time it lands on that side in succession, you will get another dollar.

But the first time it lands on the other side, the game is over.

What is the expectation value of your winnings?