## Double Pendulum and Why We Can Never Predict Weather

###### By Anupum Pant

A single weight, if suspended from the ceiling, forms a pendulum – A simple device whose position at any point in the future can be predicted fairly easily if the initial conditions are known.

Now, if another pendulum is attached to the bottom of this first pendulum, preferably using a rod (not a string), and is then given a good amount of initial energy, things move from a simple single pendulum to a very complicated two pendulum system.

The system turns so chaotic that it is impossible to make two of such exactly same systems, forget keeping them synchronised. Even if every mass and ever little distance is carefully calculated and two such systems are constructed, it would be impossible to drop them from the same height and see them move in the exactly same manner.

That is because even if they are really dropped from the same position, they’d in reality have a very tiny difference in some parameter, which would eventually become so huge that the two systems would soon go out of sync. Initially they might really seem like they are moving in a synchronized motion, but that doesn’t stay for too long.

This is also the reason why we’ll never be able to predict the weather perfectly. Nikola explains…

## Gravity Explained

###### By Anupum Pant

I’m always amazed by how teachers all around the world come up with fantastic ideas to make science easier for kids. A couple of months back we saw a video of Dan Burns using a trampoline to explain the space-time warping at a Physics Teacher SOS workshop in Los Gatos High School. In fact there is even a place on the web where you can learn it to do yourself [here].

Another explanation which came around much later just takes the cake. EdwardCurrent uses a “space-time stretcher” to demonstrate how gravity, well, stretches the space-time fabric. Moreover, the material he uses to construct this teaching aid comes mostly amongst all the old stuff lying in his garage.

## The Weissenberg Effect

###### By Anupum Pant

Remember the time we talked about a boiled egg spinning on a pool of milk? If you don’t then it’s good to know that if you do spin a hard-boiled egg on a pool of milk (or any relatively viscous liquid) the milk mysteriously climbs the side of the egg, reaches the equator, and then sprinkles around beautifully. It’s fun to see it happen. This is something similar…

The thing we see today is called the Weissenberg effect and this is how it works.

You take a spinning rod and put it into a solution of liquid polymer (which is usually very viscous). And when you do that, you see that the liquid polymer magically climbs the walls of the rod.

Some liquids reach a little high and never beyond. While others can climb up really high. The difference in heights to which different liquids can climb to is demonstrated in the following video very clearly. The three liquids used in it are as follows:

1. Guar gum solution crosslinked with sodium tetraborate
2. Pancake batter
3. and Dyed glue crosslinked with sodium tetraborate.