Some physics questions

[Chipsonfire]

Chipsonfire,

I think you have a misunderstanding of the nature of the strong and weak interactions. I've already surpassed my public nerdity quotient for the week so I'm not going to go into real detail, but they are not responsible for atomic bonding.

While a simplification, the strong force is what holds the nuclei of atoms together, overcoming the electrical force of the protons electrical repulsion to one another. The fact that it works only for short distances (well it decreases in strength as the inverse cube of distance) is why large nuclei are unstable and radioactive.

The weak interaction is responsible for Beta decay.

Neither of them have anything to do with one atom bonding with another atom.

Hmm, you're right lol. It's been too long since I've done that >_< I'll just keep my mouth shut then

 

[eedre]

I've already surpassed my public nerdity quotient for the week so I'm not going to go into real detail, but they are not responsible for atomic bonding.

This may be, but I checked on your Nerd to Bassist Ratio (NBR) and it's getting up there, so be careful.

 

[Mr.Chucklebunny]

BigO covered things fairly well, if not briefly, so I'll comment on the questions themselves.

I don't care what one has or has not not taken in school, these questions suggest that you may not be the most observant or aware person around. This is the kind of stuff I was asking when I was a young child, not in high school. Perhaps before taking physics (or any class) you should consider learning the basics of how the world works - in fact books of similar titles such as "How Things Work" might be a great start.

They're not stupid questions at all - just very odd as these are the sorts of things I learned so early that it seems like I've always known them.

Interesting points, Jeff. Like you, I am an amazingly observant person. For example, I noticed right away that you were a self-righteous jackass. High five!

 

[Jared Lash]

Hmm, you're right lol. It's been too long since I've done that >_< I'll just keep my mouth shut then

Well I hope I didn't come off as rude with my response, as my intent is just to try and share what little I know. I've had the good fortune of having a lot of really bright people do the same for me.

Jeff, I see a problem with people not questioning how the world around them works, but I don't think it matters when in their life people ask those questions as long as they ask them and seek out the answers.

 

[Geoff St. Germaine]

i read the other day, in fact, that it had always been thought that things don't stick together because of coulomb repulsion, but it's actually because of the pauli exclusion principle. pretty wild.

Hey Brad, where were you reading that? Got a link (or was it a book/mag)?

 

[Brad Barker]

Hey Brad, where were you reading that? Got a link (or was it a book/mag)?

i've been reading so many science blogs...

heck, i've got the time. lemme try to find it.

ah, crap. can't find it. well, i'm pretty sure that i didn't make it up, as i would have never thought of it!

here's my physics blog list:

backreaction
cosmic variance
physics and physicists
the quantum pointiff
quantum quandries
science and reason




FOUND IT! it was when i was wasting time at "work," reading wikipedia biographies of physicists i didn't know much about.

freeman dyson: Invalid Link Removed (check out "career")

here's the reference: F. J. Dyson, A. Lenard, J. Math. Phys. 8, 3, 423-434 (1967); F. J. Dyson, A. Lenard, J. Math. Phys., 9, 5, 698-711 (1968); E. H. Lieb, W. Thirring, Phys. Rev. Lett. 35, 687-689 (1975).

 

[Brad Barker]

Ok, first question. This might be stupid, but what keeps atoms bonded to other atoms? As in if two pieces of wood from the same tree are set next to eachother, why dont they bond? I know its a stupid qeuestoin, but what is stopping them from doing so?

here's the real answer:

Another seminal work by Dyson came in 1966 when, together with A. Lenard and independently of Elliott H. Lieb and Walter Thirring, he proved rigorously that the exclusion principle plays the main role of stability of bulk matter [6]. Hence, it is not the electromagnetic repulsion between electrons and nuclei that is responsible for two wood blocks that are left on top of each other not coalesce into a single piece, but rather it is the exclusion principle applied to electrons and protons that generates the classical macrosopic normal force.

wikipedia link: Invalid Link Removed

 

[Chipsonfire]

Well I hope I didn't come off as rude with my response, as my intent is just to try and share what little I know. I've had the good fortune of having a lot of really bright people do the same for me.

Oh, not at all. I can totally respect when someone sets me straight when i say something stupid lol. I appreciate the fact that you didn't call me an idiot, because I certainly acted like one

 

[Geoff St. Germaine]

here's the real answer:

wikipedia link: Invalid Link Removed

Interesting.

For those not familiar with the Pauli exclusion principle:

http://en.wikipedia.org/wiki/Pauli_exclusion_principle

Basically it states that no two Fermions, which are particles with half-integer spin (ie 1/2, 3/2, 5/2, etc), can occupy the same quantum state. A boson, a particle with integer spin, is free to occupy the same quantum state as another boson. Fermions are matter particles like protons, electrons and neutrons whereas bosons are force carriers like photons, phonons, W & Z bosons and interestingly, Cooper pairs of electrons in superconductors.

 

[Jeff Moote]

Jeff, I see a problem with people not questioning how the world around them works, but I don't think it matters when in their life people ask those questions as long as they ask them and seek out the answers.

I agree that it doesn't matter when - at least not to you or I - but I think people should make this a priority early in life, not just when it becomes necessary for schooling. In this case I think the OP is definitely on a good path as he seems honestly interested in the answers, but I was simply pointing out how our society needs a shift toward education about the sciences early in life. I grew up on Bill Nye and the Discovery Channel and while those seem very basic and simple to me now, they were perfect when I was 5-10yrs old.

I'd rather be a self-righteous jackass (as Chucklebunny chose to call me) than not know what I do today for having been an inquisitive child.

btw, thanks Brad and Geoff for the side discussion of Quantum mechanics. You guys know way more than me about this stuff, so it's nice to be told where to do my reading so I'm not completely lost. This reminds me how much of that stuff I've learned and since forgotten

 

[The Lynchinator]

This is a pretty cool thread.

I also have some questions about physics, but this is more on the astronomical level. I know that gravity is what keeps us in orbit of the sun, and what keeps the moon in orbit of us, but why does gravity only pull us so far towards the sun? I mean, if the suns gravitational pull is so strong, why doesn't it pull us all the way into the sun. It would make sense to me that if theres a natural force pulling on something, it's going to keep on pulling on it until it no longer can, whether that be because it has pulled the object into itself or because theres something else pulling on the object to the point where the two forces find a place where they can both hold the object (that probably made no sense, sorry). So what is it that keeps our planet revolving around the sun rather than simply colliding with it?

 

[Fontaine]

Lately I've been thinking more and more about physics, and i have some questions, though they may be stupid. Im gonna be a junior, and havent taken physics, but read alot and watch a lot of videos on youtube, so thats why i have been thinking about it.

someone needs to get laid

 

[ThatGermanDude]

This is a pretty cool thread.

I also have some questions about physics, but this is more on the astronomical level. I know that gravity is what keeps us in orbit of the sun, and what keeps the moon in orbit of us, but why does gravity only pull us so far towards the sun? I mean, if the suns gravitational pull is so strong, why doesn't it pull us all the way into the sun. It would make sense to me that if theres a natural force pulling on something, it's going to keep on pulling on it until it no longer can, whether that be because it has pulled the object into itself or because theres something else pulling on the object to the point where the two forces find a place where they can both hold the object (that probably made no sense, sorry). So what is it that keeps our planet revolving around the sun rather than simply colliding with it?

centripetal (?) forces.
basically any object wants to keep its state of motion (speed and direction), this is called momentum. this force( momentum) balances the gravitational pull from the sun.

i know this not completely correct, but going in the right direction.
i'll just wait for the experts to correct me

 

[Jared Lash]

I know that gravity is what keeps us in orbit of the sun, and what keeps the moon in orbit of us, but why does gravity only pull us so far towards the sun?

Interesting side note, but technically the Moon doesn't orbit the Earth. Both the Earth and the Moon orbit their common center of gravity, which because of the Earths larger mass is actually inside the geometric bounds of the Earth.

So what is it that keeps our planet revolving around the sun rather than simply colliding with it?

Basically ThatGermanDude is on the right track. The Earth is traveling at just the right speed to keep it in a roughly circular orbit (technically an ellipse with the sun at one foci) instead of being pulled in.

Below is an illustration used as an example by Newton of a cannon on the top of a very tall mountain:
[Invalid or Expired Link Removed]

Basically, if the cannon is fired, the cannonball will travel a certain distance before falling. Because the Earth is curved, the cannonball will travel further at any given speed than if the earth were flat. At a certain speed, the ball will travel fast enough that the distance it falls vertically each second is the same as the curve of the earth. At this point the gravitational force is constantly pulling it inward but it falls "around" the earth.

The same is happening with the earth and sun. If the sun's gravity were to suddenly disappear, the earth would go flying off on a tangent, like a rock at the end of a string if the person let go. But since the gravitational interaction between the earth and sun is always pulling the earth toward the sun, the earth simply orbits.

I hope that makes sense.

 

[bburk]

centripetal (?) forces.
basically any object wants to keep its state of motion (speed and direction), this is called momentum. this force( momentum) balances the gravitational pull from the sun.

i know this not completely correct, but going in the right direction.
i'lll just wait for the experts to correct me

That's partially correct.

The state you describe is called 'orbit'.

Centripetal force is used to describe the outward force a body applies as it changes direction. However, orbit is basically a state of free-fall due to gravity with the caveat that it's lateral motion prohibits it from ever reaching the source of the gravity well.

Imagine that you are falling from space directly toward the center of the earth. This would be the state that most people think of when they hear 'free-fall'. Like a sky-diver, you would eventually hit the ground.

Now imagine that you are also moving laterally to the ground at such a speed that no matter how far you fall, the ground is always sliding out from underneath you. In essence you are continually falling toward the source of the gravity. The velocity of the lateral movement must be precise and consistant however, in order to maintain this state. Add a little more and you will slowly spiral out into space, a little less and you spiral into the ground.

That's somewhat of an oversimplification as the orbiting body also exerts force on the body that it is orbiting, but for large ratios of mass, this effect can be practically ignored.

Fun fact: the Earth's moon is actually in a receding orbit and both it's average distance from Earth and its orbit time (currently about 28 days) are gradually lengthening.

 

[bburk]

Basically, if the cannon is fired, the cannonball will travel a certain distance before falling. Because the Earth is curved, the cannonball will travel further at any given speed than if the earth were flat. At a certain speed, the ball will travel fast enough that the distance it falls vertically each second is the same as the curve of the earth. At this point the gravitational force is constantly pulling it inward but it falls "around" the earth.

Ahh yes, the Newton-cannonball thing. I forgot about that. Nice work.

The same is happening with the earth and sun. If the sun's gravity were to suddenly disappear, the earth would go flying off on a tangent, like a rock at the end of a string if the person let go. But since the gravitational interaction between the earth and sun is always pulling the earth toward the sun, the earth simply orbits.

Don't forget to mention why it would take more that 8 minutes from the time that the Sun 'disappears' for the earth to stop orbiting the place where the Sun used to be...

 

[Jared Lash]

Don't forget to mention why it would take more that 8 minutes from the time that the Sun 'disappears' for the earth to stop orbiting the place where the Sun used to be...

A bit longer if you consider the refraction of light in the Earth's atmosphere.

There really needs to be a nerd smiley. . .

 

[ThatGermanDude]

no, it would only take 8 minutes until we'd notice that we're not orbiting anything anymore

and bburk and TheBigO, i knew what i wanted to say, i just couldn't find the right words. thanks for elaborating

EDIT: i really can't spell

 

[bburk]

no, it would only take 8 minutes until we'd notice that we're not orbiting anything anymore

Instinctively, that's what I would think too. But seriously, the Earth would orbit an empty bit of space for those 8 and some odd minutes.

and bburk, i knew what i wanted to say, i just couldn't find the right words. thanks for elaborating

No problem, IMO TheBigO gave a better explanation.

 

[Brad Barker]

Don't forget to mention why it would take more that 8 minutes from the time that the Sun 'disappears' for the earth to stop orbiting the place where the Sun used to be...

gravity waves ftw. (quadripole moments in general relativity ftl )

it's so strange that we haven't been able to detect them yet, even though we've known that they should exist for such a long time!

the LISA project that is intended on detecting them seems so sci-fi: Invalid Link Removed