Questions from an amateur

[Nano]

I have been interested in science my whole life, but got no education, and I have therefore lots of questions I don't get to ask anyone. I try here with some of the questions I wonder about the most, and I hope you have the time to help me.

 

First about the gravitational attraction between objects: Will an object in orbit gradually slow down its speed due to gravitation, and eventually hit the object which is pulling on it? For example the moon in its orbit around the earth. Has the moons speed been grater earlier in time?

 

What keeps the electron in its orbit around the nucleus? There must be some kind of force pushing it forward, or else it would get sucked in by the electromagnetic attraction between positively and negatively charged particles.

 

Why does the speed of light have the velocity it has? I know the photon is massless, but what “resistance” is stopping it from going faster in vacuum? I have heard that c is like a cosmological speed-limit, but why is there such a speed limit?

 

Why will light always move at c towards you no matter how fast you are moving?

 

And finally what dose c have to do with e=mc2 ? What is the connection between the rest-energy inside atoms, and the cosmological speed-limit? And why is it squared?

 

Lots of stuff here.. You don't have to answer all

[J.C.MacSwell]

I'll start. A slowly decaying orbit will actually increase in speed as the orbit decays.

[Sisyphus]

Under normal circumstances, gravity alone won't cause an orbit to decay and crash. The shape of an orbit (excluding outside influences) is an ellipse. When orbits do decay, with satellites and stuff, it's generally because of friction with the (extremely thin) atmosphere. This causes it to lose energy and "fall" lower down, which actually gives it greater velocity.

 

The Moon doesn't have that problem. However, it hasn't always been in the same orbit, and it is changing to this day. This is because of tidal forces. Tides happen on Earth because the near side of the Earth is closer to the Moon than the far side, making different parts of it have slightly different gravitational attraction. This causes the slight "stretching" that we experience as rising and falling ocean levels, and creates a slight "friction" effect in the Earth's rotation. The Earth's rotational energy is very gradually being transferred to the Moon's orbit, causing the Moon to "higher" (further away) by a couple inches a year, and slower (higher orbits have more potential enery and are slower). The same effect once applied in reverse, although due to the difference in size it was much greater in reverse, and the Moon has long since transferred all possible rotational energy, leaving one side always facing the Earth. This is called "tidal locking."

[iNow]

What keeps the electron in its orbit around the nucleus?

Electrons don't orbit the nucleus. That idea is based on the Bohr model of the atom, which is outdated and not very accurate. The electron instead is better described as within a probability cloud.

 

Also, it's the nuclear force which keeps electrons in their orbital shells, and which prevents them from "falling into" the nucleus from electromagnetic interaction.

[swansont]

Electrons don't orbit the nucleus. That idea is based on the Bohr model of the atom, which is outdated and not very accurate. The electron instead is better described as within a probability cloud.

 

Also, it's the nuclear force which keeps electrons in their orbital shells, and which prevents them from "falling into" the nucleus from electromagnetic interaction.

 

You might want to rethink this. The nuclear force, by definition, doesn't affect electrons — it only affects nucleons (neutrons and protons)

 

As to the original question, in general you don't need any force to keep something in motion — that's the natural state of things. You need a force to cause an acceleration, i.e. a change in velocity. For this reason and also for the one iNow mentions above, the question is ill-formed. If one were to ask, "why don't electrons collapse into the nucleus?" the answer will be from quantum mechanics: the energy of the system is quantized, and the lowest energy state is not one where the electron falls into the nucleus— it turns out you can't confine an electron on a space that small. So while the electron can be near or inside the nucleus (and on occasion interact with it via the weak force), it won't stay there.

[iNow]

Thanks for helping me to correct a misconception. I'll do some more reading, for sure.

[Nano]

Thanks for all the answers.

 

the Moon has long since transferred all possible rotational energy, leaving one side always facing the Earth

 

But if the moon has lost it's rotation, isn't it to expect that also the earth will after a great time loose it's rotational speed due to the orbit around sun? Will then the earth's orbit be further away from the sun and it's speed be greater? In that case, another ice-age might occur.

 

Bohr's solar-system model is obviously printed in my head, and I guess it gives not the right impression of an atom.

 

What about these things?

 

Why does the speed of light have the velocity it has? I know the photon is massless, but what “resistance” is stopping it from going faster in vacuum?

 

I have heard that c is like a cosmological speed-limit, but why is there such a speed limit? Why will light always move at c towards you no matter how fast you are moving?

 

And finally what dose c have to do with e=mc2 ? What is the connection between the rest-energy inside atoms, and the cosmological speed-limit? And why is it squared?

[Sisyphus]

But if the moon has lost it's rotation, isn't it to expect that also the earth will after a great time loose it's rotational speed due to the orbit around sun?

 

It would, except that it would take much longer than the lifetime of the sun.

 

Will then the earth's orbit be further away from the sun and it's speed be greater?

 

Further away, but slower. Farther orbits have more energy in the same way that dropping something from a greater height releases more energy. However, it is also slower. This makes sense if you keep in mind that gravitational force decreases the farther away you go.

[Klaynos]

A quick question that Sisyphus and the op might want to think about is, if the moon has no rotational energy as you state, how could one side always face the earth as it orbits? You might want to use a ball or similar to think about this...

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Merged post follows:

Consecutive posts merged

Why does the speed of light have the velocity it has?

 

I don't know. I'm not sure it's answerable at present.

 

I know the photon is massless, but what “resistance” is stopping it from going faster in vacuum?

 

The permittivity and permeability of free space. Why they have the values they do, I cannot tell you.

 

I have heard that c is like a cosmological speed-limit, but why is there such a speed limit?

 

This is a result of special relativity. It is derived by the simple idea that the laws of physics must be the same in all inertial reference frames.

 

Why will light always move at c towards you no matter how fast you are moving?

 

This is the same answer as the last question

 

And finally what dose c have to do with e=mc2 ? What is the connection between the rest-energy inside atoms, and the cosmological speed-limit? And why is it squared?

 

The full equation is:

 

E² = p²c² + (mc²)²

 

It is the total energy equation and can be derived within special relativity, using the same simple premise I mention above.

 

I can't remember the derivation off of the top of my head to explain where all the terms come from, it shouldn't be too hard to find online though.

[Sisyphus]

A quick question that Sisyphus and the op might want to think about is, if the moon has no rotational energy as you state, how could one side always face the earth as it orbits? You might want to use a ball or similar to think about this...

 

I didn't say it had no rotational energy. I said it had transferred as much as possible.