Physics question

[FIRE'd@51]

donheff - the speed of light is 3 x 10^8 m/s. When the atoms collide, they are traveling at 22 orders of magnitude less than the speed of light (see post #54).

[kumquat]

And if they hit head on at near light speed you wouldn't have two H atoms, you'd have 1 He atom and a bunch of superfluous energy.

[freebird5825]

Quote:

Originally Posted by Meadbh I think they would come together if they had a sufficient attraction to each other. Whether they would collide or waltz around each other would depend on their conflict management skills. I got a B+ in physics.

I majored in Physics for my Bachelor's degree. I earned an A in Atomic and Nuclear Physics. I donated that book to the local library a looooong time ago.
I was intentionally staying out of this thread because it requires higher level thinking and equations, something I gladly gave up when I FIREd.

However, this answer drew me into the vortex. I vote it to be the best answer so far.

[FUEGO]

Quote:

Originally Posted by Zero With some basic assumptions, like the universe is a sphere, and that it's finite and that the atoms are the only 2 objects in that non-expanding or contracting universe, here is a simple Newtonian view of what should happen.

What you are saying is it would take 1750 trillion trillion trillion trillion years for these two atoms to collide (using your assumptions). That's pretty close to infinity. Do universes last that long? How did this universe get created and why were the hydrogen atoms so far apart and not moving? Somebody's got some 'splaining to do. I would turn this physics learning moment into a metaphysics learning moment!

[Zero]

Quote:

Originally Posted by FUEGO What you are saying is it would take 1750 trillion trillion trillion trillion years for these two atoms to collide (using your assumptions). That's pretty close to infinity. Do universes last that long? How did this universe get created and why were the hydrogen atoms so far apart and not moving? Somebody's got some 'splaining to do. I would turn this physics learning moment into a metaphysics learning moment!

I had the same question, i.e., "Would the universe exist when the atoms collided?" And if not, where did the atoms go? Did they gradually fade away like Dorian Gray or quickly like the House of Usher?

[FUEGO]

Quote:

Originally Posted by Zero I had the same question, i.e., "Would the universe exist when the atoms collided?" And if not, where did the atoms go? Did they gradually fade away like Dorian Gray or quickly like the House of Usher?

Do two hydrogen atoms a universe make?

If a matter-less DW lived in this hypothetical universe, I bet she would always be freezing and trying to turn up the thermostat.

[Zero]

Quote:

Originally Posted by FUEGO Do two hydrogen atoms a universe make? If a matter-less DW lived in this hypothetical universe, I bet she would always be freezing and trying to turn up the thermostat.

Ut oh, careful how you use that term "matter-less DW" or the universe could get very much colder

[dizzy]

Assuming this is strictly a newtonian problem, I see the following errors with the quantitative solutions so far:

- zeros solution contains the error that the radius of separation is a function of time as the particles move together. Thus the force (and therefore acceleration itself) will increase over time.

- Fired@51's solution is more elegant taking the conservation of energy approach. However his solution contains the error that the gravitational potential energy depends on the radius of initial separation of the atoms, not the radius of the atom itself.

[FIRE'd@51]

Quote:

Originally Posted by dizzy - Fired@51's solution is more elegant taking the conservation of energy approach. However his solution contains the error that the gravitational potential energy depends on the radius of initial separation of the atoms, not the radius of the atom itself.

No, it doesn't. The R in my formula in post #54 is one atomic diameter, i.e. the center-to-center distance between the atoms when they collide (i.e. their surfaces just touch).

[Zero]

Quote:

Originally Posted by dizzy Assuming this is strictly a newtonian problem, I see the following errors with the quantitative solutions so far: - zeros solution contains the error that the radius of separation is a function of time as the particles move together. Thus the force (and therefore acceleration itself) will increase over time.

Can we take a look at a detailed solution that you have produced?

[dizzy]

Quote:

Originally Posted by FIRE'd@51 No, it doesn't. The R in my formula in post #54 is one atomic diameter, i.e. the center-to-center distance between the atoms when they collide (i.e. their surfaces just touch).

I see. You are looking at the difference in potential energy of the system at collision radius vs. initial radius and making the assumption that the initial radius term is vanishingly small. I understand your thinking now. I didn't see the initial radius in your calculation and jumped to the conclusion that you had made a typo. Actually, this a quantitative version of the escape velocity solution proposed M Paquette in #13.

Quote:

Originally Posted by Zero Can we take a look at a detailed solution that you have produced?

I'm with Fire'd@51. Your solution assumes a constant acceleration, which would imply a constant force independent of position, which is not the case for 2 bodies traveling towards each other.

[donheff]

Quote:

Originally Posted by dizzy I'm with Fire'd@51. Your solution assumes a constant acceleration, which would imply a constant force independent of position, which is not the case for 2 bodies traveling towards each other.

Why doesn't the force continually increase (inverse to the square of the distance) as the particles approach one another? I am still not clear on why, given a sufficient distance apart at the start) the particles wouldn't accelerate to approaching the speed of light.

[FIRE'd@51]

Quote:

Originally Posted by dizzy I see. You are looking at the difference in potential energy of the system at collision radius vs. initial radius and making the assumption that the initial radius term is vanishingly small. I understand your thinking now. I didn't see the initial radius in your calculation and jumped to the conclusion that you had made a typo. Actually, this a quantitative version of the escape velocity solution proposed M Paquette in #13.

Yes, that's exactly what I did. And yes, the speed I calculated is the escape velocity.

In a Newtonian framework, in which the atoms are treated as rigid spheres, they would undergo a totally elastic collision and rebound back to their initial separation.

[FIRE'd@51]

Quote:

Originally Posted by donheff Why doesn't the force continually increase (inverse to the square of the distance) as the particles approach one another? I am still not clear on why, given a sufficient distance apart at the start) the particles wouldn't accelerate to approaching the speed of light.

The gravitational force does increase inversely with the square of the separation as the atoms approach each other. However, this force is much too small to accelerate the atoms up to the speed of light before they collide.

To prove this to yourself, go back to post #54 and use the equation for the speed I derived. Plug the speed of light in for V and solve for R.

[nun]

Two things to think about.

How long would it take the atoms to start moving assuming that gravitons move at the speed of light?

Also as EM force is orders of magnitude stronger than gravity wouldn't that be more important, after all it's the EM force that binds the H2 molecule together and not gravity

[DoraM]

In 8th grade we were asked what would happen if a strangelet crossed the event horizon of a black hole. I answered C).

[M Paquette]

Quote:

Originally Posted by DoraM In 8th grade we were asked what would happen if a strangelet crossed the event horizon of a black hole. I answered C).

Then there are the 'universal answers':

5

KVAR load increases.

Power follows steam demand.

[nun]

Gravity is really a red herring here. Let's consider our universe to be a few of angstroms wide. It's obvious that the EM force between the atoms is far larger than the gravitational force and than the atoms will sink into a nice cozy potential well. Now as we increase the separation it becomes a question of whether the EM force due to the slight polariztion of the H atoms becomes less than the gravitational force.

[arebelspy]

When the atoms collide... Would they make a sound?

[Gumby]

Quote:

Originally Posted by M Paquette Then there are the 'universal answers': Power follows steam demand.

Why yes. Yes it does. But I thought the other answer was 7