# What forces keeps electrons from falling into nuclei?

1. Sep 1, 2011

### treehouse

1. The problem statement, all variables and given/known data
"What force keeps the electron from falling into the nucleus of the atom?"

2. Relevant equations

3. The attempt at a solution
I have three hypotheses:
1. Neutrons have a negative charge (although there is not only electron capture but also b+ decay)
2. The electrons in the orbital(s) repel each other (although this would suggest the repulsive force is stronger than the attractive one)
3. The electrons continue in the same direction on the very edge of the protons' ranges of attraction because they both have the same amount of attraction (the protons wouldn't pull them any more than they would pull the protons. Or would a speeding electron go as far as its momentum would carry it until it got sucked to where its momentum brought it to curvature of a proton's attraction?). How does angular momentum plug into this conceptual framework?

2. Sep 1, 2011

### PeterO

Might I ask what force stops the Space Station from falling into the Earth?

3. Sep 1, 2011

### treehouse

Wikipedia says it has a propulsion system. Why?

4. Sep 1, 2011

### PeterO

Well that just shows how wrong wikipedia can be!!!!!! Unless that reference is related to the equipment on the space station rather than what any of it is doing at the moment.

My car has an engine, but it is doing nothing at the moment - my car is in the garage.

When a golfer hits a long drive - what keeps the ball in the air? What stops it falling?

5. Sep 1, 2011

### treehouse

I need a deeper answer than the "momentum" because the collection of atoms composing the ball eventually runs out of it and succumbs the to attractive force of a much larger composition of atoms' gravity.

I (sometimes) think "when a golfer hits a long drive, the chemical forces of the body cause an interaction between the electrostatic parts of the iron and the ball resulting in an increase in velocity in the opposite directions of where the interaction occurs".

6. Sep 1, 2011

### PeterO

Momentum isn't a force.

For the golf ball - nothing stops it falling, but nothing stops it travelling horizontally either [a little bit of air resistance actually]. It takes a few seconds to fall to Earth, by which time it is many metres from the golfer. It loses most of its momentum when it eventually hits the ground.

For the Space Station, nothing stops it falling, it is just that the curvature of the earth is such that the surface "falls away" at the same rate, so it never gets any closer.

EDIT: I think the electrons are in a similar condition, though not necessarily in a stable circular orbit, more a heaving eliptical orbit.
Alternatively one can say that the attraction of gravity supplies just enough force for the Space Station to continue in circular motion with a radius of .... [fill in correct value]

7. Sep 1, 2011

### treehouse

Momentum represents kinetic force, right?

You're saying the space station follows the Earth with the same velocity Earth orbits Sol?

8. Sep 1, 2011

### Yuqing

Momentum and "kinetic force" are different concepts (I'm not actually sure what a "kinetic force" is, I assume kinetic energy). As for the discussion, refer to http://en.wikipedia.org/wiki/Newton%27s_cannonball" [Broken].

Last edited by a moderator: May 5, 2017
9. Sep 1, 2011

### PeterO

Momentum isn't kinetic force either . momentum is momentum

Space station does not have the same velocity [angular velocity] that is reserved for the communications satellites that are much higher up.

Close in where the space station is, the period is about 100 minutes.

Way out where the Moon is, the period is about 29 days

Somewhere in between we get a period of 24 hours - that is where the communication satellites are - the Iridium Series for example.

Think of it like this.

If you push a ball off the edge of a bench, it falls to the ground a few cm from the bench.
If we project it sideways with a bit of speed, it may land a whole metre from the bench.
Go faster - it lands 5m away.

We now have to move into the mind.

If the walls were removed and the ground smoothed out we could send the ball off fast enough that it would land 200m away.

Go faster - it would land 10 km away.

faster still - 1000km away

by this time, the curvature of the Earth will be coming in to play and the ball actually had "further to fall" - over the horizon.

Faster still - 10000 k away.

Faster still and it will land 24000km away - beside the bench on the other side after doing 1 lap.

OK go faster, and the rate at which the ball falls will exactly match the rate at which the Earth curves away and we have achieved orbit.

Of course Air Resistance will have mucked all that up, but if we can put our "ball" up high enough, the air resistance will be insignificant and the "ball" will continue to orbit for several years - our satellites.

btw: go too fast and the earth will curve away faster than the "ball" falls and our "ball" will head out into the universe - like the Voyager probes -unless it is on a collision course with another planet or star.

10. Sep 1, 2011

### treehouse

11. Sep 1, 2011

### Ray Vickson

"What force keeps the electron from falling into the nucleus of the atom?" You may not like the answer: it is quantization of energy levels! This issue was of great importance before the advent of quantum mechanics, because accelerated charges give off radiation, and calculations showed that in classical physics, all the electrons would radiate so quickly that they would spiral into the nucleus in a matter of seconds. Why stable atoms could exist while at the same time being composed of a nucleus and orbiting electrons was a genuine mystery.

The other answers you have been given essentially neglected this radiative aspect, as though electrons behaved like planets going around the sun. That is not the case at all.

RGV

12. Sep 1, 2011

### SteamKing

Staff Emeritus
To be clear, neutrons do not have a negative charge. Neutrons are electrically neutral, which is why they are called neutrons, instead of negatrons.

13. Sep 2, 2011

### treehouse

I like your answer except that I do not have the conceptual framework to understand 'quantization' as a force. Please provide it.

14. Sep 2, 2011

### treehouse

I thought that perhaps they have a negative charge that is so dampened that it is negligible for our methods of detection but not negligible for subatomic particles.

15. Sep 2, 2011