Apr. 14, 2009

Alex and the Principle of Inertia

by Guest Blogger

As it turns out, Spring break is great for science experiments. There's plenty of time and plenty of scope, especially if the weather is lousy and you have a curious five-year-old.

So, Alex decided that he wanted to do three experiments while he was on break. We found them – as we have found most of the things we have done – in Pop Bottle Science, which features 79 easy experiments that are not too time-consuming or messy. And in addition to a book full of experiments, the Pop bottle breaks into two, yielding both a container and a funnel as necessary.

Firstly, Alex wanted to blow bubbles. You know those little bubble-blowing kits that you can buy that contain a small bottle with some kind of detergent in it, and have a hole on a dipping stick that you have to blow through? The bubble blowing experiment in Pop Bottle Science is based on the same principles.

Get a large bowl of water, and then add a few squirts of detergent and a spoonful of sugar. (The sugar is to help strengthen the mixture and thicken the bubble wall so it doesn’t pop too quickly. I’m guessing this is the reason why bubble gum is so sweet, although I don’t know that for sure.) Then dip the top half of the pop bottle in the mixture, and blow through the neck of the bottle.

At first, Alex blew too hard, and the bubbles popped immediately. But once he got the hang of it, the gentle, sustained stream of air that he sent through the Pop bottle neck yielded fantastic results. Big bubbles formed, grew, and then hung off the bottle neck like pendulous fruit.

Next up: an experiment to make a raisin ballet. A simple premise: add four tablespoons of vinegar and three tablespoons of baking soda to a half a container of water and then throw in ten raisins. The combination of vinegar and baking soda creates carbon dioxide, which should make the ten raisins rise and fall in the water, creating a raisin ballet.

Or not so much a ten-raisin ballet as a pas de quatre. We only managed to get four of the raisins to rise and fall. Even after we threw in some more vinegar and baking soda to liven things up, the six uncooperative raisins would not budge. It was a bit like an experiment we tried a while back to get a grain of rice to rise and fall in a glass of carbonated liquid. It took us a while to get that one right, too.

Lastly, Alex wanted to explore the principle of inertia. This started with a discussion we had about how if you pulled a tablecloth out from under a bunch of dishes, there was a chance the dishes would stay in place. Instead of putting the whole dining table at risk, we decided to try it on a micro level. We put a card on top of the empty bottom half of the Pop bottle, put a quarter on top of the card, and then Alex flicked the card to try and make the quarter fall into the container.

It took Alex a couple of tries to get the trajectory right. At first he was flicking the card upward, which dislodged the quarter. But eventually, he was flicking the card straight ahead, making the quarter fall into the empty container below. This one, Alex loved. He still likes to do it from time to time, just to make sure that the principle of inertia hasn’t changed its mind.

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