Balloon rocket

My toddler has recently taken to trying to sing "Zoom zoom zoom, we're going to the moon" whenever he sees a picture of a rocket (he can't quite say all of the words, but his actions are so enthusiastic that it's very clear what he's trying to sing!), and his brother enjoys filling in the words he can't yet pronounce, so I thought they might find a rocket-themed activity fun.  On a day when none of us were feeling very well, I went for a simple setup.  I have no doubt that the engineering of this one could be improved with a little thought and we may try to refine it in future!

We used some string (I found garden twine first, but in hindsight something a little smoother would have less friction and therefore work better), a plastic straw with the bendy bit cut off, a balloon and some sellotape.  We also used a clip of the sort used for sealing food packets, but you could use a clothes peg or make do without.  I put a knot at the end of the string and threw the rest of it from an upstairs window, closing the window so it trapped the string and the knot stopped it slipping through.  No doubt better ways to anchor it at a height but it worked!

First balloon rocket

At ground level, I threaded the straw on, then tied it around our empty water table.  This meant that if little people ran into it, the water table (which is pretty light when empty) moved rather than them running into a tight, fixed string.  Alternatively you could tether it to something above head height, but I wanted my 3 year old to be able to reach it easily.  

I inflated the balloon, clipped the end to stop the air escaping and my 3 year old helped me to sellotape it onto the straw.  We then sang Zoom Zoom, and at the end of the countdown, we took the clip off and the rocket zoomed up the string to the window!  

This works because the air inside the balloon is under pressure (which is why it's hard work to inflate it) and when there's somewhere the air can leave it is forced out, and this propels the balloon forward.  If you do this without the straw and string, the balloon goes in a fairly random direction, but the straw and string guide it upwards.  We did this quite a few times, replacing the sellotape every few runs as it came fairly loose each time the balloon deflated, and replacing the balloon after an unfortunate incident where it was popped!  

Second balloon rocket

When my husband asked my 3 year old later why the rocket had gone up, my son said it was because I'd blown into the balloon really hard.  Not quite the explanation I'd have given, but he'd linked the effort I put in with the energy that ultimately propelled the balloon upwards.  Next time we do it (I'm sure there will be a next time, the littlest keeps pointing to the bedroom window and saying "Zoom zoom"...), I will get him to feel the air being expelled from the balloon and maybe start to talk about forces in terms of pushes and pulls.