# How do you perceive these lines to be rotating?

1. Feb 16, 2016

### Spinnor

In graphs c, d, e, and f below the red and blue pair of lines appear to be rotating about the horizontal axis. I'm curious how these graphs appear to others. When the lines are at the top do they appear to move towards or away from you?

Thanks for playing!

To me the top parts at first appeared to be moving towards me but I knew that it could have been either way perhaps. With a little training I could convince myself that the opposite were true, that the tops of the lines moved away from me and thus appeared to be rotating in the opposite manner.

2. Feb 16, 2016

### Staff: Mentor

They just appear to be moving up and down to me.

3. Feb 16, 2016

### Spinnor

No wrong answers, I don't see that! Thanks for playing.

4. Feb 16, 2016

### phinds

It's subjective. Some people will see it in any one of at least 3 ways; at top moving towards you, at top moving away from you, at top moving down. This kind of optical "confusion" is totally common and normal.

5. Feb 16, 2016

### Spinnor

But what do you see?

6. Feb 16, 2016

### phinds

I can see it any way I choose.

7. Feb 16, 2016

### Spinnor

It took me a while to see them rotating in both directions. Thanks.

8. Feb 16, 2016

### Staff: Mentor

Aw, thanks, I thought I failed.

9. Feb 16, 2016

### DiracPool

I'm not what your source is for that animation, but they appear to be the real and imaginary solutions to harmonic oscillators. In such a case, the pink and blue waveforms would oscillate 90 degrees out of phase with one another but, more importantly, would rotate through a 3-dimensional complex plane OUT of the plane of my computer screen and then back IN. So maybe that undercurrent has biased me, but that is what I see, a collection of phasors rotating in 3D through the complex field space, not just up and down.

10. Feb 16, 2016

### Spinnor

You know too much! You are disqualified! Just kidding. If you look at lines when they reach the top do you see the top coming toward you are away from you? When I look I always see the top coming toward me and it takes some effort to see it rotate the opposite direction. It was taken from Wiki on Quantum Mechanics,

https://en.wikipedia.org/wiki/Quantum_mechanics#Harmonic_oscillator

Thanks!

11. Feb 16, 2016

### DiracPool

Well, the thing is that there is no answer for that, you can train your mind to interpret either way. It's the same thing as with a necker cube.. I guess what I'm saying is that the answer is capricious. Some times I see it rotating toward me (clockwise), sometimes the reverse..

12. Feb 16, 2016

### Spinnor

Last edited by a moderator: May 7, 2017
13. Feb 17, 2016

### Staff: Mentor

I'm with @phinds - It started out up and down. Then they seemed to change behavior depending on where my 'center of vision' was relative to a given graph. I guess you'd call this a "gif"-ted trompe l'oeil. ...sorry :(

14. Feb 17, 2016

### OCR

15. Feb 17, 2016

### Staff: Mentor

I see them moving up and down, but I can also see them rotating in either direction if I want.
At least with C and D, I can also see the two curves rotating against each other, colliding twice per rotation. E and F are too fast for that.

16. Feb 17, 2016

### phinds

Ha ... sorry my a**. You're not sorry at all. You did that on purpose! I go by the dictum that only MY puns are funny, so this one sucks. Of course if I had thought of it, it would be hilarious.

17. Feb 17, 2016

### Sophia

I see them going up and down. I can make them rotate in both directions, but I think I would not see the rotation if you haven't mentioned it in the first post.

18. Feb 17, 2016

### zoobyshoe

I see the upper parts rotating out of the plane toward me in the cases of C, D, and H. The more complex ones won't maintain a steady direction of rotation and sometimes seem two dimensional.

19. Feb 17, 2016

### DrGreg

Here's an illusion where you can't help seeing the wrong direction of rotation alternating with the correct direction.

20. Feb 17, 2016

### Bandersnatch

I have a preference to see the lines rotating towards me on the top, but then it's very easy to switch to the other way around.

This one, on the other hand:
https://en.wikipedia.org/wiki/Spinning_Dancer
Took me so much longer now than I remember to make myself see a counter-clockwise rotation.
(I see it was also included in OCR's link)