# Why does the earth go round?

1. Jan 29, 2007

### Raza

It seems like a childish question, but why does the earth go around the sun? Why not stay in a single place?

2. Jan 29, 2007

### Staff: Mentor

It can't stay in a single place because of the force of gravity. It has to either orbit the sun, fall into it, or fly away from it.

3. Jan 29, 2007

### arildno

Of course, in the Earth's rest frame, the Earth is, indeed stationary. At all times..*

*I know, it is dumb, but I couldn't resist posting it anyway..

4. Jan 29, 2007

### Averagesupernova

The earth is flat too. :rofl:

I'm just jerk'n your chain. As with you, neither could I resist posting.

5. Jan 29, 2007

### complexPHILOSOPHY

Reserve the jerk'n for a special occasion.

6. Jan 30, 2007

### Raza

I still don't get of why it must orbit around the sun.

7. Jan 30, 2007

### Staff: Mentor

Could you explain more about what you don't understand...? If you pull on a door handle, why does it open?

8. Jan 30, 2007

### americanforest

The planets and sun came from a slowly spinning mass of cosmic gas. Since angular momentum has to be conserved now the planets go around the sun. I'm no astronomer so the description might not be perfect, but it's generally true.

9. Jan 30, 2007

### ranger

When we drop something to earth from a reasonable height, it falls to the earth in a straight line. If we however were to stand and throw a ball at a certain angle, it will fall to the earth along a curved path. If it were possible for us to throw it hard enough, the ball will follow a curved path, but would always miss the earth, hence it would be falling to the earth, but always missing. Therefore, it is in orbit around the earth.

The same principle can be applied to the earth. It is falling towards the sun, but it moves sideways fast enough i.e enough tangential velocity to always miss the sun. Like the ball in orbit around the earth, the earth is in orbit around the sun.

10. Jan 30, 2007

### Wizz

Nice one Ranger. Simple and short. Now he should understand it.

11. Jan 30, 2007

### Raza

I got it!
Thanks
but something must have "pushed" the earth in order to rotate?

12. Jan 30, 2007

### Ki Man

When the solar system was formed, the dust gathered into rotating disks and the planets were formed from the dust, so the earth was already floating when it was created, along with its 23 former brothers and sisters

13. Jan 30, 2007

### Raza

If I were to create my own solar system, duplicating everything to the last atom but except, there was no "push" given to the planets, what would happen?

14. Jan 30, 2007

### Staff: Mentor

It would all collapse into the sun. However, that is a very unlikely condition to have. Zero is one number of infinite possibilities, and it is pretty much impossible to have a perfectly symmetrical, perfectly static cloud in a dynamic universe. In fact, scientists are finding that a pretty decent fraction of stars that we are able to make observations of have planets orbiting them. Given the limits of our current ability to find such planets, then, it is not a stretch to say that it is likely that most stars have systems of planets orbiting them.

Last edited: Jan 30, 2007
15. Jan 30, 2007

### Cyrus

You made the earth and LTI system, nice.

16. Jan 31, 2007

### vanesch

Staff Emeritus
All things that do not have enough angular momentum (rotation, say), fall into the sun. So the only things that CAN, after a while, survive in a solar system MUST have sufficient angular momentum! Call this the "anthropic principle for planets"

17. Jan 31, 2007

### chemisttree

Imagine that the earth and sun were stationary with only the attractive force of gravity between them. They would move closer to each other unless acted on by another force and eventually collide. What other force might prevent the earth from colliding with the sun if the earth were stationary? Could the gravity of another body exactly balance the gravitational attraction of the earth to the Sun? Maybe it could for a short time but that hypothetical gravitational source would also be attracted to the sun and move closer... unless some other force opposed its motion toward the earth/sun.

If the earth were motionless, to be stable you would have to introduce a repulsive force like a coulombic force (electric charge both positive or both negative). If that were the case, I think every day would be a bad hair day!

Or you could start the earth moving at a right angle to the sun and let centripetal force (supplied by gravity in this case) act to change the earth's linear motion into a circular or elliptical orbit. Apparently, this is how the solar system formed. All the bits that were stationary were sucked up into the sun or flung away on wildly eccentric orbits and lost. That which remained was "selected" by speed and direction to eventually become the planet earth.

18. Feb 1, 2007

### tehno

Still childish ,but more interesting question,is why does the Earth turn around itself.Perhaps crazy ,but still correct answer is :Becouse nobody wants to put and effort and stop it (fortunately).
Hehehe.

19. Feb 1, 2007

### Raza

I was just going to ask that.

20. Feb 1, 2007

### disregardthat

What I'd like to know is if the earth ever will bash into the sun. Or will it's orbit continue forever, taking out that the sun will collapse someday.

I have heard that in space there is not entirely vacuum, so after extremely long time, these atoms would stop the earth enough to make it go swoop into the sun? Or would it's kinetical energy be empty someday so it would fall into the sun.