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Me and my friend were doing the bottle flip challenge when after a few unsuccessful attempts, my friend told me to add more water to increase the chances of a successful flip.

So my question is

Does a bottle flip really depend on its water content?

From what I get from my observation is that one could get more control if more water is added to the bottle. However, if you add even more water, you end up losing control.

So, is there an optimal water level which maximises the chances of a successful flip?

PandaScientist
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    Related: https://physics.stackexchange.com/questions/384470/can-you-calculate-exactly-if-a-bottle-flip-will-be-successful, https://physics.stackexchange.com/questions/326346/the-physics-of-bottle-flipping, https://physics.stackexchange.com/questions/151001/flipping-a-bottle/151023#151023 – kricheli Aug 08 '23 at 20:26

2 Answers2

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The most optimal amount of water inside a bottle seems to be between 20 and 41 percent full.

Factors that come into play is how the water can spread inside the bottle while in the air. The rearrangement of the water changes the rate of rotation (because angular momentum is conserved). The rearrangement of the water changes its moment of inertia $I$ which slows down the rotational velocity making it easier to land upright. It also reduces the chance of rotating and tipping over when landing on the bottom. If the rotation is slower the friction of the table has higher chance of stopping the bottle in rotating.

$$ L=I\dot{\theta} $$

Some undergraduate physics students have analysed the bottle flipping with cameras:

https://www.utwente.nl/en/news/2018/9/309591/university-of-twente-students-unravel-the-physics-behind-the-perfect-water-bottle-flip

https://www.youtube.com/watch?v=E98-GcJb4qI

bananenheld
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Part of increasing your chances to successfully land the bottle flip is having a low center of gravity (to avoid it tipping over when it is landing and not exactly vertical). If the bottle is empty, the center of gravity is roughly at half the height. If you partially fill it with water (enough for the water to outweigh the (say plastic) bottle itself), the center of gravity will approximately be at half the water column's height. Increase the amount of water and the height of the center of gravity increases as well, up until the point where it is back at half the bottle's height for a completely full bottle. Somewhere in between there must be a sweet spot which given a shape of the bottle and weight of the bottle it should be easy to calculate.

All that being said, of course this is not the only effect playing a role here.

kricheli
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