When I was asking my children for ideas on where we could get air molecules in motion to power our pinwheels, my oldest suggested perhaps if we held it over hot water it would move. He remembered conversations we had before about hot air rising and how birds, clowds and gliders use it. I asked him to think what would happen if we held it over a pot of hot water and he admitted he didn’t think it would work unless the pot was boiling and steam was rising.
My real goal for the activity was not pinwheels at all. I wanted to challenge my kids to figure out how to test a hypothesis. I wanted to see if they could come up with explanations for the results. As an added bonus I got to talk more about air molecules moving around and transferring energy. A filled balloon has potential energy. It takes energy to force those air molecules into it and then it can release the energy pushing molecules out.
The kids have been looking again at Walter Wick’s I Spy: School Days book. Their favorite page is of a balloon popping machine and we have spent numerous hours attempting to create our own variation of this. The task allows us to explore force in so many different ways. Does the falling marble have enough force to move a toy train? How much force is necessary to pull a small pulley? They gain experience in measuring force and estimating how much force something has or needs. They gain problem solving abilities. How can we reduce friction? What is preventing a particular gear from turning? Kids need to experience potential energy and have chances to talk about it. Setting up the contraptions they can see where potential energy exists. None of their machines have been as beautiful or complex as Walter Wick’s, but some have also included pretty complicated mechanisms. Some of what they know right now is wrong, but they are getting better and better at explaining things.
Soon I hope to see if we can use our own little pinwheels in the contraptions. Can we blow strong enough to push a pinwheel which turns an axle and triggers something else to happen? Or can we use the pinwheels as fans, with something else turning the axle and then have it create enough wind to nudge a balloon hanging on a string next to it? With every attempt the children learn more about estimating the amount of energy needed for a particular set-up.
We’ve also speculated about how we could add chemical energy to the system. I’m not keen on using fire but we have some tentative ideas around trying to harness the energy baking soda and vinegar. The question would be how to get the chemicals to mix at the right time but to have something on top that would get moved by the rising gasses. We haven’t figured this out yet, but we will sometime. Problem solving is an important skill to learn.