Finally, and explanation for the bead chain fountain

My self siphoning beads video presented a puzzle... Why do the beads rise up above the rim of the pot before they fall to the floor?

The problem eventually came to the attention of academics at Cambridge University, John Biggins and Mark Warner. And I'm happy to say, we have an answer! In a published scientific paper no less.

It was published in the Proceedings Of The Royal Society A and can be read here.

They also put together an explainer video:

My favourite part is where they call it the Mould Effect. I've never had an effect named after me before!

The surprising top line explanation is that the pot pushes the beads up. It sounds crazy but the way to reach this conclusion is to consider an idealised version of the chain; a chain of rods. As each rod is pulled into motion, the opposite end of the rod is forced downwards (as the rod rotates around it's centre of mass). The reaction force from the pot is where the extra upward force comes from. The links between beads make the chain somewhat ridged and in that way it acts like a chain of rods. Anyway, watch the video or read the paper or both, their explanation is great.

Like all good scientific ideas, this explanation makes testable predictions. Firstly, that a larger drop will result in a higher fountain. This is certainly the case. It also predicts that a chain built from more loosely joined beads would not produce the fountain effect because they would not act at all like rods. Watch their video to the end to see this tested.

Finally, Biggins and Warner have used the bead chain fountain problem to inspire young physicists to look at real world practical problems. You can find their resources here.

4 Card Puzzle

Here's an interesting puzzle that tells us a little bit about the way we think.

Did you get it right? Let me know in the comments.

Pillow illusion

I discovered an illusion when I opened my eyes this morning. I happened to be looking in the direction of 2 stacked pillows and the dark region where the two pillows met appeared to expand for about a second. I noticed it worked better when I was looking at a bright part of one of the pillows instead of the dark region itself.

I've recreated the effect below. To make it work, close your eyes for 10 seconds. When you open them, immediately look at the grey dot. The dark region in the middle should appear to expand for about a second:


Pillow illusion


I'm not sure if this has been done before or even if it works for anyone but me! Let me know if it works for you.

My theory is that when you first open your eyes, your pupils are dilated, so a lot of light is coming in. As a result, the dark patch looks less dark. In the fractions of a second after you open your eyes, your pupils contract. Less light gets in, so the dark patch gets darker. Because there is a gradient from the middle outwards, that darkening could also be interpreted by your brain as the dark patch expanding.

It might be that other things are happening besides your pupils contracting. Your brain does all sorts of adjustments to the information coming from your eyes.

Film camera operators talk about white balancing before taking a shot. It's where they make adjustments to their camera so that things that are supposed to look white actually do end up looking white. Your brain does some pretty intense white balancing too and it leads to a phenomena known as colour constancy. There's also brightness constancy going on in your brain. And if this brightness constancy takes any sort of time to kick in, that could also be an explanation for the effect in this illusion.



Self siphoning beads

Here's a quick video I made of my self siphoning beads:

The chain is the stuff from vertical blinds. The thing you pull on to open and close them. Searching for metal 4.5mm bead chain on ebay gets you the right sort of thing. That also bring up the linkages you'll need to buy to make the chain really long.

The reason it self siphons is that the chain pulling down outside the beaker is longer (and heavier) than the chain pulling down on the inside of the beaker.

The reason the chain loops up higher than the rim of the beaker is a bit of a mystery. I think it's to do with the fact that the beads are changing direction and it can't do that instantaneously as that would represent infinite acceleration. So a big loop is formed. I don't know, something like that.

UPDATE 28/06/13

This video was posted on Reddit where it got loads of upvotes and it's been seen by hundreds of thousands of people. Thanks Reddit! It was seen by Earth Unplugged who invited me to film it in slow motion. Here's that video:

Reddit is great for discussions, here's the original thread. And it was discussed at length in the sub reddit Ask Science. And here is a brilliant analysis from user Silpion with videos and images.

The sound from a vibrating rod

I made a video to show you the cool way a rod of aluminium vibrates when you hit it:

Why is purple weird? A video for the Royal Institution

I was giving my Illusions talk at the Royal Institution and had a few minutes at the end to film this video about purple.

Arguing with Matt Parker about Pi and Tau

Numberphile is a great youtube channel about maths. They invited me and Matt Parker on to fight about the circle constant. Here it is:

You can also follow Matt on twitter. And catch us both live in Festival Of The Spoken Nerd.

Talking about Benford’s Law for Numberphile

Numberphile is a great youtube channel about maths.  They invited me on to talk about Benford's Law. Here it is:

Here's my earlier post about Benford's Law.

Make your socks last longer with a Euclidean rubber glove switch

Your left hand and right hand are mirror images of each other. There's no way you can position your left hand so that it looks like a right hand. It will only look like a right hand if you look at it in a mirror.

There are molecules like this in chemistry. Molecules that can't be positioned in such a way as to look exactly like their own mirror image. These are called chiral molecules. We talk about them having a handedness because they share this property with our hands. Continue reading →

Turning a webcam into an infrared camera

Turning a webcam into an infrared cameraThe sensors in digital cameras pick up more than just visible light. They pick up a lot of infrared too, that's light below red that we're not able to detect with our eyes.

This can make pictures look funny, so manufacturers add a filter to block the infrared and give you a more natural image. Actually the filters don't do a perfect job and if you fire a TV remote control at your camera phone you should see it light up on the screen.

All this means you can have a bit of fun with your old web cam. You can remove the infrared filter then add a visible light filter so your webcam only sees infrared!

Continue reading →