# Spin of the planets

1. Jun 20, 2010

### luckis11

First question:

"The planets spin in the same direction they orbit". What does that mean?: A roulette ball (when rotating inside the roulette) spins in the same direction it orbits, or in the opposite direction it orbits?

2. Jun 20, 2010

### mgb_phys

Imagine the planets are wheels running on a track (with the track on the sun side of the planet) they rotate in the same way as the wheels

3. Jun 20, 2010

### luckis11

I don't understand what you mean. Can you please answer my question EXACTLY as I formulated it?

4. Jun 20, 2010

### mgb_phys

A roulette ball rotates with it's rotation axis point toward the center - planets don't rotate like that. They rotate in the same way as ball bearing in a cage.

5. Jun 20, 2010

### phyzguy

If I look down on the solar system from above the Earth's north pole, the planets revolve around the sun in a counterclockwise direction. Seen from this vantage point, most of the planets are also spinning in a counterclockwise direction. However, this is not strictly true. Venus' spin is retrograde, meaning from the above viewpoint it would be spinning clockwise (albeit slowly). Uranus axis is tipped over on its side, so that its spin axis is nearly in the same plane as the planets orbit.

6. Jun 20, 2010

### luckis11

"The planets spin in the same direction they orbit". What does that mean?: A roulette ball spins in the same direction it orbits, or in the opposite direction it orbits? So,there are only 2 possible ways:

No1.) The planets spin in the same direction as the roulette ball
No2.) In the opposite direction

What applies for the planets? No1 or No2?

Last edited: Jun 20, 2010
7. Jun 21, 2010

### phyzguy

Why the obsession with the roulette wheel? Go back and re-read mgb_phys' post. As he says, the axis of rotation of the ball on a roulette wheel is in the plane of the roulette wheel's rotation. This is not how the planets rotate.

8. Jun 21, 2010

### luckis11

Why should be a puzzle to understand what you mean? The more easy is to undertsand a teacher, the better teacher he is. Is there an IQ competition in here that one prooves he is clever when he solves the puzzle of what others mean?

It's indefferent whether the roulette wheel is moving or not, as what defines the problem is simply that the ball is moving on the non-moving wall of the roulette. Why don't you answer my question with a "No1 or No2"? Because neither of No1 or No2 applies? Why? Forget it, I will not understand you. Please stop posting so someone else does.

Last edited: Jun 21, 2010
9. Jun 21, 2010

### Calluuuum

Firstly, no need to get annoyed when people are only trying to help.

Secondly, (no offense) your question is rather stupid.

You've just said the same thing just replacing the noun. Why would there be another option to something you just repeated?

The planets spin in the same direction they orbit. This explains itself. If the planet orbits counter-clockwise, it spins counter-clockwise. While not entirely true (axis tilts vary the actuall spin direction for some planets), it's an ok guideline.

10. Jun 21, 2010

### luckis11

It seems that you did not understand what I meant. I try again:

The roulette ball spins at a particular direction in relation to the direction of its linear motion (linear motion=the rotation around the roulette wall). One possible case is No1, which is what happens with the roulette ball. But the direction of its spin could be the the opposite of what it is, which is possible case No2. Possible case No2 does not happen with the roulette ball, but I am asking whether it happens regarding the planets.

POSSIBLE CASE No1:

here (up) is the roulette's wall

<----
(ball) ------------>this is the direction of the liner motion of the ball
---->

here (down) is the centre of the circle of the roulette.

POSSIBLE CASE No2:

here (up) is the roulette's wall

---->
(ball) ------------>this is the direction of the liner motion of the ball
<----

here (down) is the centre of the circle of the roulette.

Last edited: Jun 21, 2010
11. Jun 21, 2010

### Calluuuum

Look at the circles formed when you draw them out. You get option one, where they are going in opposite directions (clockwise around the roulette vs anti clockwise ball rotation), option two is both going clockwise. Now I'd like you to point out which refers to them spinning the same direction. Then I'd like you to point out how many times this has been said, by several different people. It doesn't take much to work out when two things are spinning clockwise or anti clockwise.

Last edited: Jun 21, 2010
12. Jun 22, 2010

### luckis11

Again you are not lucid. You want me to agree that what you all say is lucid? No, it's not, it's a quiz to finger out what you mean. If it was lucid I would have no problem grasping it. Why not simply answer to my question: What applies for the planets, No1 or No2?

13. Jun 22, 2010

### Calluuuum

You don't learn by having everyone give you the answer. The answer is very clear, it's been stated several times, now it's your turn to read what everyone has said. It doesn't take much effort to apply what everyone has said to your own examples. Read what I said before and actually do what it says, you'll be able to work it out yourself. You seem to be actually refusing to see it in another way. If that is how you want it though, fine, it applies to number two. This is where the ball is spinning CLOCKWISE and the orbit is CLOCKWISE. Notice how the words are the same? That's because they're spinning in the same direction.

14. Jun 22, 2010

### luckis11

Now you made it clear. I read the posts again. They are not lucid. The lucid is: "When the planets are seen to rotate around the sun clockwise, they spin clockwise. Whereas when the roulette ball is seen to rotate around the roulette wheel clockwise, it spins anti-clockwise". Or: "The planets spin in the same direction with the direction of their rotation around the sun. Whereas the roulette ball spins in the opposite direction of the direction of its rotation around the roulette wheel".

Last edited: Jun 22, 2010
15. Jun 22, 2010

### DaveC426913

Yes, luckis, it's our failing that you aren't understanding...

Frankly, I have no idea what the importance of the roulette wheel is. I have no idea which way the ball on a roulette wheel turns when it goes around the wheel, so I have no idea whether planets go the same way or the opposite way.

16. Jun 22, 2010

Staff Emeritus
If it rolls, it's orthogonal to the wheel direction. Another reason this is only adding confusion.

17. Jun 22, 2010

### DaveC426913

If you look down from the North Pole of the Solar System, all of the planets go around the Sun counterclockwise.

Simply put, most planets also rotate about their own axis counterclockwise. (Not all do. Mercury rotates clockwise. Uranus' axis is tilted over so far that it actually lies on its side.)

18. Jun 22, 2010

### DaveC426913

But if it rolls, its axis of rotation is horizontal, not vertical. So it is meaningless to talk about whether the ball revolves clockwise or counterclockwise.

[EDIT]... which is precisely what you just said... :blush:[/EDIT]

19. Jun 22, 2010

### DaveC426913

Luckis, please please the attached diagram, then go back and read the thread. You should understand why your questions couldn't be answered the way you wanted them to. The Solar System does not behave the same way a Roulette Wheel does.

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20. Jun 22, 2010

### luckis11

The motion of the roulette ball of the first case of your drawing, happens (also happens?) when the ball has slowed down and is rolling on the metal floor which has the the numbers drawn on it. When it "flies" pressing against the wooden vertical wall and does not roll on the floor, the second case of your drawing happens. Actually, even when moving on (the not exactly horizontal) floor, the first case does happen without the second case happening also. Am I correct?

Last edited: Jun 22, 2010