(viewed 4415 times)
I thought it was time to show some SCIENCE from my kids, so here we are.In the last week or two of the summer term, not a lot usually gets done, especially in the last week, where videos tend to get shown too much. I'm rather proud of myself for only showing videos on the last day of term, and instead performing SCIENCE experiments. Huzzah!Here is one of them:
Water Rocket Challenge
This is a standard challenge to build a water rocket out of readily available materials. I'm sure a lot of you have done it before. In this challenge, the task was to launch an egg along with the rocket, and to have it come back to Earth safe and intact (no hardboiling here thankyou very much!).
This task was given to a bunch of 11 year olds to do, and in the end we had two contenders, the boy's team, and the girl's team.
Water rockets work by filling the rocket with some water, and then pumping lots of air into it as well. When the pressure gets to much, it forces it's way out in the only available direction: through the mouth of the bottle. A bloke called Newton came up with a third law to explain what happens as a result of this. He said, "All actions must have an equal and opposite reaction."
Imagine you are sat on one of those wheeled swivel chairs, facing someone of a similar size to you on another wheelie chair. If you push the other person, then that person will go wheeling away from you. That's our action. However, you will also go wheeling backwards because of your push, and that's the reaction.
Another common example is the Earth's gravity pulls you to the Earth. An action. The reaction is your gravity pulls the Earth to you. (Depressing, isn't it) Hang on a minute though, why isn' t the Earth being moved around by all these gravity people wandering around then? It all goes back to that middle bit of Newtons third law, the "Equal & Opposite" bit. The Earth's pretty big, right? And you're, compared to it, really really small. So the force the Earth has on you is enough to keep your feet on the Earth. A force of equal size attracting the Earth to you, isn't going to do much, since it has to affect the entire planet, rather than just one small bag of water and bones like a human.
Anyhoo, back to the rocket. Why water? Well, it leads back to the last bit, air doesn't have much mass compared to a plastic bottle (especially if it looks like the rocket in the photo, the boy's team entry) so the force pushing that rocket upwards (the reaction to all the air pushing out of the bottle downwards) wouldn't be all that big. That's where the water comes in. Water weighs an awful lot more than air, so when that gets pushed out of the bottle, the reaction is a much bigger force, shooting that rocket much further up in the air. Too much water though, and the air can't force it all out, and your rocket is weighed down. You need to experiment to find the ideal combination!
As I said earlier, this rocket was the boy's team contribution. They got a bit carried away. ^_^
Innovations on this one include a truly amazing egg protection system. That egg was so well protected that I was willing to bet money it wouldn't break, no matter what. The egg is suspended in a half water bottle chamber by elastic bands, making a sort of suspension sling to absorb impacts. Surrounding it is a shedload of cotton wool, and surrounding that are two bags partly filled with water to provide even more of a buffer.
To give you an idea where the egg is in relation to the picture, it's pretty much in the middle of the rocket, just beneath the bottle that is used as the pressure chamber (the rocket is upside down) So it has even more protection in the form of a rigid plastic nose cone! It's a tank!
For anyone wondering about the loo rolls and plastic bags, these are parachutes they designed themselves. air is supposed to flow through the tubes, inflating the bags, and slowing it down by drag. A slight problem with the design is that they will also slow it down going up, but they were willing to lose some height for safety. And, let's face it, this thing weighs a tonne. ^_^
So, on the day of launch, this thing managed to get 8 or so feet of the ground, soaking me (the person doing the pumping) in the process. It was a majestic launch, and the egg came down fine. We launched it a couple of times, and they even through it, and that egg was safe as (incredibly well padded) houses.
Height: 1/10 Looks: 8/10 Egg Survival: 10/10
Now, onto the girl's team!