Physics for Bottle Flippers 101

“There have been school-wide loudspeaker announcements banning bottle flipping from our school,” posted one of my teacher friends on Facebook recently.

She was writing about the fad that is sweeping the nation. Forget high-tech, smartphone-addicting Pokemon Go, low-tech water bottle flipping is the new rage.

Apparently, it all started with Michael Senatore, a high school senior in Charlotte, North Carolina, who flipped a water bottle during a talent show. The video has gone viral and now, seemingly, every middle-schooler wants to do it. 

If you’re going to spend your time trying to land this stunt, you ought to understand the physics involved. Yes, I said physics.

Here are some of the terms you’re going to need to know:

• Angular momentum
• Mass
• Fluid dynamics
• Air resistance
• Inertia
• Gravity

Angular momentum is a lot like linear momentum, with which we’re all familiar. Picture this: Tom Brady throws a fast, tight spiral just over your head. As you reach up and grasp the ball, its momentum pulls your hands and arms in the direction the ball was traveling until it slows enough for you pull it in for a catch. That’s linear momentum. 

Angular momentum is the same thing but in a circle. When you flip the bottle you impart spin - that’s angular momentum. 

The spin causes the water to slosh around inside the bottle - this is where fluid dynamics comes into play. The bottle tries to transfer its angular momentum to the water but the water has a lot more mass then the plastic bottle and, because of inertia, the liquid doesn’t want to spin. Instead, because it's a fluid, it sloshes around, slowing the rotation. 

The trick is to get the angular momentum to zero when the bottle is vertical so gravity can do its thing and the bottle lands upright on a flat surface.

There’s a complex balance between angular momentum, fluid dynamics, air resistance, inertia and gravity.

There’s no reason you have to stop with a single rotation either. If you impart enough angular momentum, you should be able to do 720 degrees of rotation before landing your bottle. Of course, that makes the whole trick much more difficult.

Wouldn’t it make a great science project to build a machine that can flip a bottle perfectly every time? Hmmmmm, maybe we can tackle that challenge in the STEM Club…

Sources: The Boston Globe, Vox