# Bottle Flip Challenge (and the science behind it)

My kiddo is all about the Youtube challenges these days. She’s having a blast recreating all the challenges she can find. She is quickly adding videos to her Youtube channel. One of her latest videos was about the Bottle Flip Challenge.

It goes a little like this. Grab a few water bottles, fill them up with different amounts of water, flip the bottle and see if you can get it to land on end. 🙂 It’s pretty simple, but it is fun to try, and there’s actually a lot of science behind why it works and doesn’t work.

## Hanna doing the Bottle Flip Challenge:

You’ll notice she managed to flip and land the first two, but not the third. She tried and tried (and tried and tried) to land that almost full bottle, and it never happened.

We discussed the possibilities. She thought there must be some force in action. I thought it was about the motion of the water, and once in motion the fullest bottle was unable to stop itself in enough time to stand upright, and just kept pushing itself over.

But… you know, we’re not physicists. 😀 So we went and hunted some down.

Here’s what the physicist had to say:

Recording the motion and playing it back in slow-motion helps reveal what is going on. As the bottle moves through the air the liquid inside it starts to climb the sides. This increases the bottle’s moment of inertia and so decreases its rotational speed, much like a diver who extends his arms and legs to slow his spin.

Trying different amounts of water shows how important it is to get the amount of liquid right. The trick just doesn’t work with a full bottle. The  liquid can’t move, and its higher centre of mass means that a full bottle topples over when it lands. Filling it to just a bit below a third seems to be optimal.

You can read the full article and explanation, along with their video and a great illustration of the diver here.

This is what I love about homeschool… you can take a seemingly silly looking Youtube challenge and it ends up being a pretty fun way to learn about physics. Even if you’ve never taken physics in your whole life, there’s bound to be someone out there with the answer. 🙂

Are your kids flipping over the bottle flip challenge? I’d love to hear how they did, and if they defied physics and managed to make the full bottle stand! Tell us all about in the comments!

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