Diver in a bottle

Ethan asked to do some science today, so I pulled out an old favourite of mine.

 This is supremely easy, and easy to play with, so great for little hands. Bonus - it doesn't make a mess.

You only need 4 components, a bic (or very similar) pen lid, blu tack or similar, a clear plastic bottle and the water to fill it.

Use a tiny blob of blu tack to clog the hole at the top of the pen lid, and a slightly larger blob to weight the tail. This will be your diver.

Fill the bottle to the brim. We used a 2 litre bottle as it's easier to see and the diver has further to go up and down, but I guess it would be fine in a smaller one. Test your diver's weight. Keep adding blu tack until it floats like this -

 You want it to just float, with just the tip poking out. Too much weight and it'll sink to the bottom and you've got to start over, though I suppose you could test this part in a cup. Probably should have thought of that while doing it! Screw on the lid, wipe up the overflow, and your done!

Squeeze the bottle, and he dives. Let go, and he comes back up. Simple! If you hold it just right, you can even make him stop at any point.

 Yes, the diver is red in this photo and the video. I didn't take progress shots while doing it and couldn't be bothered to fish him out afterwards. And the boys wouldn't have relinquished him had I tried.

How does it work? The science is actually really simple too, in case you were wondering. Squeezing the bottle forces water up into the diver, compressing the air. This increases the density of the diver, and he sinks. When you release it, the reverse happens, the air re-expands, the diver is to all intents and purposes lighter (technically, less dense) and he floats. I love science!

Instant hit! It's quick, mess free, and they can help do it without causing a stress. The only downside, if you can call it that, is that if they get too excited and knock it over or shake it, the air bubble comes out and you have to get it all out and start over. However it's so fast to do that it's no big deal.

For Science!

Update: This blog has now moved to www.undomesticaited.wordpress.com - Hope to see you over there!

Squeezing the bottle causes the diver to sink because the increased pressure forces water up into the diver, compressing the air at the top of the eyedropper. This increases the mass, and density, of the diver causing it to sink. Releasing the squeeze decreases the pressure on the air at the top of the eyedropper, and the water is forced back out of the diver. - See more at: http://www.stevespanglerscience.com/lab/experiments/eye-dropper-cartesian-diver#sthash.FXg7Q158.dpuf

queezing the bottle causes the diver to sink because the increased pressure forces water up into the diver, compressing the air at the top of the eyedropper. This increases the mass, and density, of the diver causing it to sink. Releasing the squeeze decreases the pressure on the air at the top of the eyedropper, and the water is forced back out of the diver. - See more at: http://www.stevespanglerscience.com/lab/experiments/eye-dropper-cartesian-diver#sthash.b3Uo4Pyf.dpuf

Squeezing the bottle causes the diver to sink because the increased pressure forces water up into the diver, compressing the air at the top of the eyedropper. This increases the mass, and density, of the diver causing it to sink. Releasing the squeeze decreases the pressure on the air at the top of the eyedropper, and the water is forced back out of the diver. - See more at: http://www.stevespanglerscience.com/lab/experiments/eye-dropper-cartesian-diver#sthash.FXg7Q158.dpuf