Building bridges, pulleys and catapults

As we wrap up the first phase of this semester, children are rapidly finishing up their projects. The creativity and persistence being displayed by everyone is so infectious.

We should see videos from each child next week, but here is a sneak peak.

Some of the designs …

Look at the craftsmanship of this catapult …

… the creativity …


and the struggles …


Don’t get fooled by how simple this looks, it shoots like crazy …

French call it Bricolage … we call it Jugaad … I call it brilliant. A wonderful way to demonstrate the pulley mechanism … sewing machine anyone?


Complex contraptions that are still evolving as we build them …


Simple but no simpler way to build a catapult out of pencils …


Some awesome bridges that go above and beyond the original design … unstoppable creativity

Can’t wait to see all the projects being finished soon … and post the videos online.


Shooting the monkey and floating the watermelon

Today was probably super high on fun and learning quotient.

The idea was to continue exploration of Newton’s laws and the concepts of weight / weightlessness. People often confuse weight and mass. Mass is not easily changeable. It’s more real. Weight is experienced. That was the theme of the initial discussion.

We talked about why weight is felt due to the ‘Normal force’ acting on us. So if the Normal force doesn’t exist, weight cannot be felt. That’s what happens in free fall. If the elevator is in free fall you feel weightless.

This is what happens with astronauts in space. They ‘feel’ weightless.

A rising elevator makes you ‘feel’ heavier. A falling elevator makes you ‘feel’ lighter.

We talked about the science behind simulating weightlessness on earth. In fact I could show it in the living room by jumping off the chair with a watermelon in my hand … and using the slow motion camera on my phone.

Then came the crown jewel of our program. The shooting monkey experiment.


That’s me dressed up as a hunter !!

It’s a sad story of a monkey being shot by a hunter. The monkey (Fred) is hanging by the branch.

The hunter aims perfectly to shoot the monkey. All should go as per plan and sadly the monkey should get shot.


The monkey is smart. It let’s go as soon as it sees the flare of the gun.


The hunter is smarter. He expects the monkey to let go and decides to adjust for the falling monkey. He has three choices.

(A) Leave it as it is (B) Lift it up even more (C) Lower the gun to catch it falling


What would you recommend?

We built an interesting mechanism to demonstrate this phenomenon (Built by our intern Kautilya and my two sons). We had so much fun.

From next week we will be starting the journey of building our projects.

Our inspiration is the Classical Mechanics lecture by Walter Lewins. (Watch from 35:03). Hats off to the master.

Turn right to go left. Makes perfect sense


Doc Hudson: I’ll put it simple: if you’re going hard enough left, you’ll find yourself turning right.
Lightning McQueen: Oh, right. That makes perfect sense. Turn right to go left. Yes, thank you! Or should I say No, thank you, because in Opposite World, maybe that really means thank you.

In the famous movie Cars there is a scene about Hudson Hornet teaching McQueen how to race on a dirt track. Our session today was about exploring the science of turning corners and why this works in some cases.

Here are the scenes we watched.

McQueen failing to make the turn …

Hudson Hornet explaining what he needs to do and then showing it …

We started with the basics. A rotating object will have a tendency to continue in the same path.


This is the implication of Newton’s 1st law. Path of inertia.


Yes we can still turn a sharp corner while riding a car or a skateboard. Thanks to friction in our wheels. But, if there the corner is too sharp, we usually have banking to increase the friction.


In this case the dirt road doesn’t offer enough friction and there is no banking. So the car will tend to drift and spin.

The rear wheels will over rotate causing the car to spin. Happens when you turn on ice too. To compensate you need to turn the front wheels away from that spin and also ensure the back wheels are horizontal offering maximum friction. You steer into the turn.

Counter intuitive.

You can see this in many car racing movies.