(089) Rocket Science

I've been using water bottle rockets for years to teach forces/energy conversion etc, but yesterday I had my first failed launch. Water was getting back into the air tube from the bottle so I thought the problem must be with the valve. I dug out an old inner tube tonight, cut the valve from that and fitted it into the air tube. Now, even with a (good quality (Lezyne brand)) mini-pump I can easily achieve a decent air pressure in an empty 2 litre plastic bottle, so confidence is high for a second rocket attempt tomorrow.