# Rotations, Speed and Directions by eye (may be biology)

1. Jun 12, 2006

### Mt. Nixion

I have a problem thinking about rotations. As we all know, it takes 360 degrees to complete a circle, 720 to do two rotations, 1080 for three full rotations, 1440 degrees for four and 1800 for five and so on. My question is, what is the amount of complete rotations a human eye can see in one second? Also, what is the maximum speed a human can completely see and lastly, how many changes in directions can the human eye see?

2. Jun 12, 2006

### rcgldr

Figure skaters and divers rotate pretty quickly in the air, but experienced viewers have no trouble keeping up with the number of turns. Jugglers generally toss objects with a double or triple flip. Of course the person doing this has to be able to time it or have a good sense of what is going on. A quadruple back flip followed by an overhead view of a double twisting double layout off the flying rings from the 1970s:

Last edited: Jun 12, 2006
3. Jun 13, 2006

### brewnog

It's not a question of rotation, speed or number of changes in direction. Your eyes don't have any trouble following a fighter jet a couple of miles away do they? Or seeing bubbles forming in a champagne glass?

The eye itself can't cope with anything moving across its field of view of more than a couple of degrees per second. Note this has NOTHING to do with how fast something is spinning; if a skater is spinning 200m away you'll have no problem seeing this, if it's only a metre away your eye alone will not be able to track it. This is a reason why your eye is capable of moving in its socket; and your head on your neck.

There's some excellent information on Wikipedia if you fancy doing a search.