Pump up the volume
I've often used balloons as the theme for a design lab exercise and was wondering how to give it a new twist when I came across these mini pumps on eBay. They were really cheap so I wasn't expecting much. So, when they arrived I wasn't surprised that they didn't work. After a couple of pumps the balloons just didn't get any bigger. I stuck them in a drawer with the rest of my rubbish. Today I had some time to kill so thought I'd see what was wrong with them. What I found was that they actually work perfectly well. The first couple of pumps make the balloon grow quite rapidly but after that the rate of growth gets less and less. I had previously thought that the air must be leaking out or something but it wasn't.
Great, that's me sorted for the lab next week then.