Its been about two weeks since I watched this video about rolling shutter and also this video by Matt Parker whom I mentioned last time. Matt was showing the effect on fidget spinner, the new gadget that you simply spin and there is nothing really special about it (except that it spins).
Rolling shutter is the effect made by any “picture taking device” (as far as I know). So, for example camera or scanner (in my case). When cameras take pictures, they do so by scanning from top to bottom and saving up line by line of pixels. Similarly, how scanners do it except much faster so that you do not notice it. Scanner on the other hand is slow enough that when something is moving the pictures won’t make any sense. If I would move an object with the scanner, at the same speed it would smooshed across the whole picture because it does not see everything at once, only a thin line.
Really interesting stuff starts to happen when you spin something so that it goes back and forth (around and around). I did exactly that and it produced for example image above or the ones to the side.
It is interesting how the twisted shapes change with the speed that the fidget is rotating. The fifth and sixth picture are part of the same thing, fidget spinner spinning and being moved by me at the same time. The first one on the collage is spinning really fast, the second one not so much the third one is changing directions and the fourth one is really slow which makes for quite “solid” fidget spinner.
I recommend to try this at home, great and easy “experiment” (of course unless you do not have fidget spinner, then I do not recommend buying (life at stake)).
The first time I really encountered object with bearings and was wondering about what they really are was about 3 years back when I was on inline skates with a classmate. There was a nice long and smooth downhill and we both drove down without much beforehand added speed. Soon he was going way faster and was still moving many seconds after me. At that point when we started to talk about it, I thought than my inline skates do not have any ball bearings, which I now think is not true, he only had clean ones since his skates were new. Probably without bearings the skates would not work.
Ball bearing. See how they do not slide, they rotate.
Ball bearings are small balls (often from metal) enclosed between two spaces that are supposed to rotate, for example on some axis. It is possible to just leave the two surfaces touching but then they just rub against each other which causes high friction. The important part is that the balls as you can see on the left, rotate, they do not slide and when circular object is only rotating instead of sliding it does not experience much of a resistance. Try it yourself. Take a pencil and toss it across table so that it does not start to turn (parallel with the direction of the movement). Remember the distance where it got and try the same thing but this time perpendicularly and see how far it gets, that is exactly what the bearings are doing.
There are lot of types made for different purposes. Since the bearings have much lower area with which they are touching they do not distribute pressure so well, also they might need cleaning often or lubrication. In fidget spinners you will of course find bearings. The ones that spin very long time are the ones with ceramic bearings.