## Watch How 32 Metronomes get Synchronized Automatically!

### Background

From biological cells to celestial bodies spontaneous synchronisation is found everywhere in the nature. In simple words, you could call “spontaneous synchronisation” as “a natural self-organisational behaviour” in things. Where, out of a chaos, uniform order starts appearing. If that feels too abstract to understand, read on…

Probably the first human to note this effect was a Dutch physicist, Huygens. Huygens noticed this when he was working on a ship with two pendulum clocks. For very long times, his work of calculating longitudes required him to watch these clocks swinging away their pendulums. He would lie on the bed and watch them go. There was one weird thing he noticed about these pendulum clocks. No matter how the pendulums started swinging, after an hour or so, both the pendulums ended up synchronized! This was a perfect example of uniform order appearing out of no where from an apparent chaos.

The effect amazed scientists for about 350 years. Only then some researchers at Georgia Tech University, were they able to produce a perfect mathematical model that proved it. So, what was happening on the boat? In a similar fashion, would all pendulum clocks in the world get spontaneously synchronized? Let’s look at the following example to find the answer.

### Synchronizing metronomes

Think of it this way. You have a couple of metronomes with you – the physical ones, the ones that are based on pendulums. You start each one of them and there is almost no chance that you’d get them perfectly synchronized in the first go. So what do you do to get them synced?

You simply keep all of these metronomes (ticking with the same frequency but different phase relations) on a free-floating table. That gets them synchronized in a matter of minutes. See how the 32 metronomes completely out of sync of each other get synchronized in the following video. Note that they are on a surface that is free-floating.

Adam Milkovich explains the effect very beautifully in the following video:

### Back to Huygens

Now, if we come to see the boat as a free-floating base and the 2 discordant pendulum clocks as metronomes, the segue of their motion into a perfectly synchronized one, makes complete sense.

The only difference is that the boat was a pretty huge free-floating base – something which has a relatively very high mass as compared to the pendulums. And then there is the drag on water; other forces etc.. The pendulums had a very very tiny effect on the boat and in turn, were able to transfer only a teeny bit of energy with every oscillation. So it took longer.

I find it pretty incredible that it even happened in an hour. I think it would have taken a much longer time, given the huge difference in their masses. May be Huygens exaggerated. Or it was a very small boat. Anyway, that is the reason, Huygens’ clocks took about an hour to get synchronized. While the ones we see above are able to do it in a matter of minutes.

### Back to the Question

Would all pendulum clocks in the world would get spontaneously synchronized?

Well, I’m not too sure. But this is how I see it:

I think of Earth as a really really really huge free-floating boat. Now, the movement of pendulums on Earth certainly has an effect on the earth. And in turn the other pendulums get affected. And they end up synchronized at some point. But the first effect itself is unimaginably small.

I mean, the Earth is so massive that even if all of the 7 billion people on Earth jumped at the same time, the 6-trillion-trillion-kilogram Earth would move so less. Earth would move about a hundredth of the radius of a single hydrogen atom.

So, pendulums would hardly have any effect. But the effect would certainly be there.

Therefore, I’d say the answer is yes. Yes, all the pendulum clocks on earth would eventually get synchronized. But it would probably take so long, that even earth, leave alone pendulum clocks, would cease existing.

Toy idea: Well, that gives me a great idea for a toy. 5 – 10 pendulums inside a huge pendulum. The inner ones would get beautifully synchronized automatically!

Hit like if you learnt something today.

## Build an Autonomous Toothbrush Robot in Minutes

### Background

If you are looking for a cool little science project, I think your search should end right here because today I’m sharing with you an awesome way to transform your toothbrush into an autonomous toothbrush robot. This one is just autonomous enough to move around on its own, hit obstacles, turn around and continue. But remember, since it is a fun project that can be completed within minutes (in under \$5), you can’t expect a lot out of this basic bot.

Also, I did not invent this thing. I happened to stumble upon a video by Evil Mad Scientist on YouTube that taught me the basic idea of how this thing works. So, cheers to him. However, since my supplies were constrained, I felt a need to find some alternative methods to construct a similar bot. I’ve shared the original video and my own alternatives (in text) under it… You can skip reading the next two sub-headings and watch the video below them.

### Here is what you’ll need:

• A toothbrush (preferably, one with angled bristles)
• A cellphone vibrator motor
• Some double side tape
• and a Button cell

### Here is what you do:

Firstly, do not worry if you don’t have the exact materials mentioned above, I’ve suggested some alternative ideas after the video.

1. Grab the toothbrush and carefully cut off the handle, we’ll just need the head. Now, this part can be the most difficult because the plastic at the neck can be pretty tough sometimes. If you are not confident, take help from an elder.
2. Use the double side tape to stick the motor on top of the head in a way that the rotating shaft of the motor doesn’t touch the bush.
3. Connect the button cell to the terminals of the motor. If the whole bot starts vibrating with the motor, It’s done. Place it on the floor and watch moving…
[Video]

### Alternatives

• Suppose you don’t have a brush with angled bristles. You can just take any other toothbrush and keep it under your mattress for a day to get pressed. The straight bristles turn into angled bristles. I had to do this, so I know.
• Now, if you don’t have a cellphone vibrator motor, you can use one of these common motors too. All you’ll have to do is stick a piece of clay or tape on the shaft to make a counter weight so the motor vibrates when it rotates. You don’t want it rotating smoothly here.
• To make the bot turn away better from obstacles, I stuck 3 toothpicks on top of the brush in a way that one of them was sticking out in the front and the other two were pointing out from the sides to form wing like structures.

It hardly takes any effort to try it out and then you’ll have your own bot moving around on the floor of your house. It feels great to watch it move like that! If you can, try making a huge variant. Use a bigger brush, pencil batteries and a bigger motor.

[See this for more details]

## Dancing Drops of Water and Dipping Hands in Molten Metal

###### By Anupum Pant

When you sprinkle water on a hot pan, you’ll find that the droplets start dancing on the surface, as if there was no friction at all. From far, this effect looks a lot like water droplets on a lotus leaf (a super-hydrophobic surface). But, the physics behind this phenomenon is completely different. Read on to find out what is the mystery behind these dancing drops of water.

### The Leidenfrost Effect

Why does this happen?
Unlike the drops on a lotus leaf, this happens at a particular temperature for a specific liquid. Different kinds of liquids display this effect at different temperatures.
For water, at a temperature when a small amount of water in contact with the pan gets heated enough to form a thin-film of vapor below the drop, water is no longer stuck on the pan (water sticks to some surfaces due to low surface tension). The drop has a thin vapor film below it which enables the drop to move around on the film. The formation of this vapor film is a continuous process, till the whole drop turns into water, one film at a time. This is called the Leidenfrost Effect.

Some liquids like liquid Nitrogen are extremely cold. At normal room temperature, they start boiling. A normal room’s floor is like a hot pan for liquid Nitrogen. So, it forms these dancing drops on a floor which is just at room temperature. You can try this yourself – If you can find some liquid Nitrogen, you can simply drop it on the floor and watch droplets moving effortlessly. They won’t stop moving!

### Dipping hands in Liquid Nitrogen

The temperature of liquid Nitrogen is around -195 degree centigrade. It is one of the coldest substances and is used with extreme caution in industries and laboratories. If it touches you, your skin can easily get burnt. Yes, burnt – at extremely low temperature. It could probably also make the dipped limb useless for life. So, you shouldn’t try stuff with liquid Nitrogen at home.

But, it turns out, you can safely dip your hand in it for a small amount of time and return unharmed. Thanks to the Leidenfrost effect. Our hot-pan like hand – for cold liquid Nitrogen – makes a thin film of vaporized Nitrogen around the whole hand. This film, protects our skin from the ill effects of extremely cold temperatures. Still, there is no reason for you to try this. It has been done already.

The crazy duo from Myth Busters tried this with molten lead. It worked!  They, of course had to wet the finger with water – for the vapor film formation.

### Water flowing uphill

Recently, an undergraduate research student group from the University of Bath found out a way to manipulate the movement of water on a specially designed surface, using this phenomenon. They found that machining ridges on the surface (and heating it) would make the thin vapor films under water droplets move in such a way, that they could use it to propel drops against gravity. They were able to demonstrate this by showing water moving uphill on a slope. It is enthralling to see it for yourself. I’ve attached their video below.