If you build this just right, by getting the water bottle as full as possible, you can make the diver go down with a barely perceptible squeeze of the bottle, which then allows you to pretend you’re controlling the diver’s movement with the power of your mind… Putting a few marks on the bottle with a permanent marker might help you turn this into a game – can you get the diver to stop at a particular height? Build two of them and you can race someone else up and down. I’m sure you can come up with your own ideas to make this particular “marvellous machine” even more interesting and fun to play with.

EXTRAS: Here’s a lovely video explaining how a submarine works. Can you work out how the deep-water diver works from this?

And here’s another video explaining how submarines work:

MORE GOOD STUFF: Click here for more activities. I’ll be publishing more videos of activities from my book over the coming weeks. Check back here, follow me on Twitter or subscribe to my YouTube channel to make sure you don’t miss them.