During my recent science class, I got introduced to a new topic on force and motion. This blog post is on the physics of bottle flipping and an exciting project for science enthusiasts. In school, I learned there is an angular motion that acts on the flipped bottle and makes it land perfectly each time. Further research, I found there is a lot of physics behind this simple task. We have all tried this or watched countless videos on the miracle bottle flip. As I watched the bottle flip, I pondered is this miracle or what is the physics behind the bottle flip. Still, it was simple physics. Now time to dive into the deep science of the miracle flip. Towards the end, you will find the art of flipping the bottle and land it perfectly.

## What is Bottle Flipping?

Before we start, let me give you a heads up on what bottle flipping is. The bottle flip challenge is a fun game where friends try to compete with each other to see who lands the bottle upright. This challenge to all over the internet. Try searching up the bottle flip challenge on Youtube. The chances are that you will find at least 20 videos. Now that we are all caught up. Let us commence.

# What is the Physics Behind the Bottle Flip?

To master the physics behind the bottle flip first, we will need to understand angular momentum.

### So What is this Angular Momentum?

An object's angular momentum depends on its angular velocity (how fast it rotates) and its moment of inertia (how much mass the object spreads out from a central point). When there is no external twist or torque (force)acting the object's angular momentum will be maintained and conserved. This is the law of conservation of angular momentum. An example of this might be when you go to the ice rink. You see a person spinning with their arms open and stretched out. At this point, the moment of inertia is high. The inertia is more when the figure skater mass spreads out from the central point or the center of the body. As the figure skater slows down, she starts to pull her arms firmly closer to her body. Now, her moment of inertia decreases. According to the law of conservation of angular momentum, to maintain the angular momentum, the angular velocity increases as she spins faster and, the inertia decreases. The same principle applies in a spinnable chair too.

Let's get back on track. I know there is still one question pondering your brain. What does this have to do with the miracle bottle flip? Try throwing a stern or rigid object, like a dice. As we all know, gravity will pull it back down. The dice being a solid object, the spread and distribution of the mass do not change as it flips in the air. Also, remember it's the moment of inertia and angular velocity that stays the same. Maybe angular momentum makes rolling dice is always unpredictable and exciting. Fortunately, a water bottle is different because it contains liquid. When the bottle filled with water is flipped, the water moves around inside the bottle. Unlike the dice, the mass of the object(bottle filled with water) distributes and spreads out. Remember the skater which we talked about earlier. Just like her, the bottle moment of inertia and its angular velocity changes. But the angular momentum remains the same as the bottle lands perfectly upright.

## How To Do a Perfect Bottle Flip?

Now to get to the exciting part, How To Do a Perfect Bottle Flip?

Drum roll, please! Time to learn how to land a bottle perfectly every time! Most bottle flipping videos have their bottle filled with water. Well, go back and look at the bottle. Most of the bottles have less than half of the bottle filled with water. Surprisingly, researchers have found out that to land a water bottle upright, you will need to have it 20% to 41% filled with water. If we try to land a full bottle, the probability of landing the bottle is less than 5%. It took more than more than an hour to land a bottle filled with water (90%) upright. This is because (just like the dice) the mass does not spread out inside the bottle. If the bottle is less than half full, the water has room to spread or distribute.

In the following videos, we have tested different amounts of water.

I hope you enjoyed this post on physics behind the miracle bottle flip. Also, just a reminder, do not get discouraged if the bottle does not land upright on your first few tries. Now you know the secret to all the bottle flipping videos. I guess that is all. Hope to see you next time. Bye!