There is More to it Than You Think!
Qin Ru Zhang
Bottle flipping is a trend that became popular after it was performed at a high school talent show. It looks simple on the outside, but further examination of the science behind it says otherwise. A few factors can influence the odds of a successful flip.
Firstly, the surface area on the bottom of the bottle, part of the kinetic energy accumulated from the flip makes the bottle bounce upon contact with the table. But why does that matter? The principal in practice dictates that with a wider surface area, the bottle will bounce less, and the odds of a perfect landing will increase. A soda bottle with prong-shaped bottom, for example, is much more likely to not land compared to a water jug with a wide contact surface. A normal water bottle is in between these two extremes.
An arguably more influential factor for a successful bottle flip is perhaps the water level. This determines the center of gravity of the bottle. The lower it is the better chances the bottle has to not tip over. Gravity pulls the bottle down and will cause it to stand back up if the center of gravity is above the tipping point. Filling 1/3 of a standard bottle should give it a low enough center of mass. If there are uncertainties in this area, giving 45 degrees of tilt to the bottle and seeing if it stands back up can verify that the center of gravity is indeed low enough. What’s next is a combination of fluid dynamics, center of mass and angular momentum. As the fluid sloshes around, the center of gravity moves with it. And when the bottle is flipped, it is given angular momentum. The movement of the water, and in extension the shifting of the center of mass, takes some spin, or angular momentum, away from the bottle. That’s why you see the bottle’s rotation slow immediately after it has been thrown. It is a result of the water moving around and adjusting to gravity, taking away angular momentum, the bottle then stops flipping in mid-air and lands straight down, pulled by gravity. Hopefully, it lands in the perfect flip considering everything mentioned above.
A perfect toss should include minimal forward momentum, and toss the bottle upward while putting a good spin on the bottle. If it is tossed with too much forward momentum, the water will keep wanting to go forward even if the bottle’s movement is stopped, therefore contributing to the bottle tipping over. To conclude, picking a bottle with a bottom that doesn’t have a small surface area, finding the right water level, and throwing it just in the right way increases the odds of a successful bottle flip. The science behind bottle flipping is more complex than what we see on the surface.