# Is gravity the cause of most kenetic energy?

1. Jul 9, 2010

### jimjohnson

What is the source of kinetic energy? If the Milky Way is moving toward the Virgo cluster at 600km/ sec, it has a kinetic energy of 4 e59 ergs. Second, take an electron "rotating" around a nucleus with a ionization energy of 15eV and then multiply by the number of electrons ,e79, for e68 ergs. There are many objects moving and spinning all with significant energy.
In the first case, is the source gravity acting over billions of years on unevenly distributed matter?
In the second situation???

2. Jul 10, 2010

### Naty1

Electrons rotating about a nucleus are governed almost entirely by electrical attraction which is billions upon billions of time stronger than gravity...gravity can be generally ignored in regard to particle interactions.

The basic source of KE is acceleration even though acceleration is not displayed in
KE = 1/2mv2. Another way to say the same thing is that a net force has acted on a mass m to accelerate it; work is done and that is reflected in the motion of the mass.

If the magnitude of the velocity remains constant, v = c, there is not change in KE and the work done by any force is zero. In uniform circular motion the speed of the particle (magnitude) remains constant and perpendicular centripetal 'force' does not work on the particle. A force at right angles to the direction of motion changes direction not magnitude.

Gravity is in general related topotential energy, that is, energy of position. By convention, the gravitational potential energy of a particle is taken to be zero at infinite distance from the center of attraction. So a particle drawn from outer space to earth's surface would have a negative potential energy, negative work is done by gravity...due to the attractive force of gravity...positive work is required to remove the particle from the influence of earth.

Any introductory college level physics text should give a more complete description....or try Wikipedia for things like "kinetic energy" or "gravitational potential energy".

Gravity causes clumping of gas cloud material to form stars,planets and solar systems and galaxies as entropy increases; dark matter spider webs may aid that formation. I suspect it is not the cause of motion between adjacent galaxies since that gravitational attraction is small. Maybe random motion from formation momentum?? Over vast intersteller distances, expansion of the universe causes galaxies to in general move apart from one another, but that effect is minimal on closely spaced galaxies.

Last edited: Jul 10, 2010
3. Jul 10, 2010

### jimjohnson

Gravity causes clumping of gas cloud material to form stars,planets and solar systems and galaxies as entropy increases; dark matter spider webs may aid that formation. I suspect it is not the cause of motion between adjacent galaxies since that gravitational attraction is small. Maybe random motion from formation momentum??

I still think gravity could be the cause of almost all star rotation and movement within a galaxy. Do you agree?

4. Jul 11, 2010

### Naty1

yes...
dark matter also is also supposedly a gravitational phenomena....gravitational effects like lensing is so far the only way we observe it....

and gravity might also be the major cause of intergalactic rotation...I tried to say I just am unsure....

I have read why some galaxies, like our own, are spiral, that is somehwat flat like a dinner plate, and others not...but I don't remember...I believe the distinction is believed to be age related....our Milky Way might be a younger galaxy....

When gas condenses to form aoms, planets, stars, etc it often tends to swirl as it moves together..and I would assume that rotational momentum is carried into the mass that evolves...that is what is believed happens with black holes and that effect causes frame dragging outside the black hole....maybe that's an engine that contributes to galactic rotation?? I don't know.

5. Jul 12, 2010

### Naty1

I happened to just come accoss some references to rotational motion of galaxies in BLACK HOLES AND TIME WARPS by Kip Thorne beginning around page 341 up almost to 356....

My comments in the previous post seem about right, but there are more specific explanations included which seem to relate to our discussion here. Thorne says (346)

It turns out all gas in the universe is slightly magnetized and the accretion of spinning gas results in some galaxies emitting vast quanitities of radio waves.....hence "radio galaxies"...

Anyway, bottom line is that gravity within galaxies, especially in the form of supermassive black holes at galactic centers, is a type of 'engine' that contributes to galactic rotation.

Last edited: Jul 13, 2010