Class 3 filled a balloon with matter. They thought it would be lighter so we put lots of children on the mat to think about which would be heavier; the mat with children or the mat without children. Interesting predictions!
So… Established that filling a balloon with ‘stuff’ made it heavier (weighing them both to check too) we moved on to removing matter!
Heating a gas makes it move around lots. We also tried this in the school hall by getting the children running about. If we did this with children on a mat, then surely they would spread about and the mat would end up having fewer children (representing gas) and be lighter?
Back outside, we heated up a balloon with a hair drier (thanks for saving us the Percivals) and then also with a small camping stove. Inside the balloon, its air was really hot and it spread about, think of it emptying out of the balloon, and therefore being lighter than the air around it. Yep, our balloon went up in to the sky! Sadly, a gust spun it round and it collapsed, making it land somewhere in Darcy’s back garden!
Word of warning: please don’t send up the Chinese lanterns that also work on this principle! Ours didn’t have a source of ignition or a wire frame making it dangerous! (Ours was biodegradable!)