# B I heard a spin-top in a perfect vacuum would stay spinning

1. Sep 11, 2015

### SciencePerson

Ok I heard that a very fast spinning top, in a perfect vacuum, on Earth, would stay spinning forever, and I suppose it would in the middle of the vacuum without falling, because spinning at lightspeed means it can't move 1 down, so if the speed in this top stays in it, then it could avoid falling and slowing~

Help :O

2. Sep 11, 2015

### Staff: Mentor

A top floating in a perfect vacuum will indeed spin forever, because there's no friction or other force to slow it down. In fact, right now you're standing on of those tops: The earth has been spinning on its axis for some billions of years now, and looks to be good for many more.

But....
This makes no sense at all. Nothing spins at the speed of light.

3. Sep 11, 2015

### SciencePerson

Yes the Earth stays spinning, but, the top is in the field of gravity! It may slow down then from pull! And fall downwards...

4. Sep 11, 2015

### Staff: Mentor

The mere presence of a gravitational field doesn't affect the spin of the top. However, if the top is touching the ground in any way, there will be some small amount of friction at the pivot point, and that friction will slow the top. If you were to put the top into orbit around the earth, it would still be in the earth's gravitational field, but it could fall freely without every touching the ground and then there would be no friction to slow it (except that space is not quite a perfect vacuum).

5. Sep 11, 2015

### SciencePerson

Wait wait wai wa hate a moment :D...are you saying gravity won't affect it just because satellites don't fall, because those are different! They move left whhhille moving down! Like this - >^>^>^>. . .BUT the spinning top may go down by gravity, plus slow by the pull................unless you (somehow) [how?] know it won't.

6. Sep 11, 2015

### Drakkith

Staff Emeritus
That's not what Nugatory is saying. He's saying that a top in free fall (under the effect of gravity) won't slow down just because gravity is acting on it. It must touch something else in order to slow down. Your falling top would start to slow down when it entered the Earth's atmosphere and began to interact with the air.

7. Sep 11, 2015

### SciencePerson

So a planet stays spinning, and if it doesn't slow by any pull, then it wouldn't fall....wait........................if the fast spin top is in the exact middle of a perfect vacuum on Earth, it stays spinning, and no fall, yet it does, and only it does for the fall....ArhhhrRR!...I'll think about this later, busy at the moment...

8. Sep 11, 2015

### Drakkith

Staff Emeritus
What do you mean by 'fall'? The top (and the planet) are still affected by gravity and are still pulled down. A top in a vacuum here on Earth would stay spinning a little longer than a top outside in the air, but not forever since friction from the ground still acts on the tip.

9. Sep 11, 2015

### SciencePerson

What I figured out is this:

If a spinning top in a perfect vacuum could avoid falling, it will stay spinning forever because the moving photons and therefore moving particles stay in it, but the reason it falls by gravity is because it gets photons OR space pull without being touched by atoms to take away the top's photons and so it also moves down, and may not fall if at lightspeed since no more room is left because the added photons or space pull by gravity don't affect the already-filled-spaces-photons in it~

If you want I can write this out clearer...

Last edited: Sep 12, 2015
10. Sep 12, 2015

### Drakkith

Staff Emeritus
That's just utter nonsense. Thread locked.