X-Peri-Mas #13 – Bernoulli Baubles

Baubles look so boring stuck on a tree… I wondered whether we could make one fly!

Watch this video and you’ll see that the air stream the ‘out’ hose of a vacuum cleaner really can make a bauble fly. I can put my hand through the stream, too, and the bauble stays flying.

How can I make baubles fly?

You need a strong flow of air – you’ll notice in the video that the bauble flies higher (futher away from the hose) when I added the attachment to make the opening narrower. If you’ve got a fancy vacuum cleaner or the type people use in their garage or workshop then you might be able to fix the hose onto an ‘out’ rather than an ‘in’ port and you’ll have a stream of air blowing. If not, you’re looking for a leaf blower for massive baubles or if you’re lucky you might be able to get a small bauble to fly on a hairdrier air stream. Try it out – I’d love to see some attempts at this on #XPeriMas on twitter!

Why are my baubles flying?

This comes down to the Bernoulli effect. There are some great videos out there already showing how big you can go with this and plenty explaining how the effect works.

The air has to go around the bauble. When the bauble is perfectly in the middle of the stream, all the air goes the around the bauble and meets back up and since it’s in all directions at once it all cancels out and all that happens to the bauble is that is gets an upwards push from the air that cancels out gravity pulling it back down.

But no ball is not perfectly round, especially not a bauble with rough edges and that seam where the two plastic halves were glued together as it was made and then there’s the bit that sticks out for you to hook it onto the tree. So some of the air tries to go around the bauble and hits a rough bit or the seam or that knobbly bit for the hook and it has to go around that as well, not just around the smooth bits of the bauble. To meet back up with the rest of the air at the top, despite going further than the rest of the air, this bit has to go faster. The air is all going to have to go slightly further and slightly faster in different places around the bauble. This means that those forces don’t all cancel out and there will be some push from side to side on the bauble!

If the bauble starts to move to one side then pretty things get really different – the air that has the bauble in the way now needs to go a really long way around while the air that now has no bauble in the way has a big shortcut and just goes straight up. This causes a big difference in pressure and that ‘sucks’ the bauble back towards the middle.

Pink shows the air is having to move further around the bauble – this pushes the ball back into the middle!

Since the bauble is never perfectly in the middle it is always being pushed one way or another and you’ll never get it to stay totally still. My favourite is when it starts to spin around faster and faster – like in the GIF at the top of the page.

Try this out – see if you can get flying baubles this Christmas!

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