This week, catapults. Simple physics, and a great opportunity for the kids to get into experimentation and engineering. Here's a video of the oldest group of kids in the design and testing phases.
The basic model that I did with every age group was the elastic-band and popsicle stick catapult, which you can find guides to all over the internet. SpecificLove on youtube has a clear tutorial.
For the 3-4 group, we used colourful popsicle sticks and worked on counting the right number of elastics and popsicle sticks for each step and picking our colours. Parents had to help with wrapping the elastic bands, but some of the kids tried it out too. Motor skills!
We added forks as launching cups, and wrapped tape around them if they broke (which actually gave them a little extra oomf).
With the 3-6 year olds, I put an emphasis on prediction by offering four launching ammunitions: cotton balls, mini marshmallows, beads, and gum. All of the kids started with cotton balls, but before they got the others everyone had to sit by the supply they thought would work best. Kindergarteners had a tough time separating the idea of what would fly best from what they most wanted to eat, though.
7+ kids got a lesson on fulcrums and catapult arms before getting the option to follow along with building the mini catapult or building one based on the models I had ready in class or inventing one altogether.
The big triangular catapult you see one of the kids testing in the video came from Storm the Castle, an excellent catapult-devoted page. A few of the kids older than 7 tried their hand at it relying only on my model for guidance, and were delighted with the result. Not giving them instructions resulted in some great problem-solving and team work, not to mention asking me some well thought-out questions.
Everyone built a working catapult.
A 7-year-old build a balloon and popsicle stick crossbow.
It was awesome.