The protagonist of the video, which could well be the captain of your school football team, performs a relative feat that is significantly amplified by the cheers of his fellow.
The feat in particular is throwing a bottle of water on a table, making it rotate until it falls into a fully vertical position.
But, although it may seem fruit of chance or of trial and error, it is actually a complex technique based on physics. Nathaniel Stern, Professor of physics and astronomy at Northwestern University, has tried to shed some light to the subject on Vox.
“Is the combination of using the right amount of water with practice and an elaborate technique”, explains.
“It is the combination of using just the right amount of water with practice and an elaborate technique”
It all starts with a twist of the wrist, which creates a specific force through called angular momentum. It is a movement similar to the classic impulse, in which an object displacement does not change its motion unless another force acting on it. With angular momentum, the same concept applies to the rotation.
“If you print him an exaggerated force, will fail you. He grabs the bottle by stopper, so when you launch it, the bottle is already turning naturally. If he seized the bottle from half, the force would not be enough”, added Stern.”
Then enters scene fluid dynamics, or what is the same, how water moves into the bottle. When the bottle is released, water moves despite the fact that it has more mass than the plastic. The weight of the water slows down the speed of rotation, so that the bottle lands squarely has to get that water ends up on the bottom of the bottle when in vertical.
Michael Senatore, the young protagonist of the video, explains that her only secret has been to practice while I was bored in school and work. But for all those who want to try the trick, Stern leaves some practical advice:
1- fill the bottle about one-third, since if there is too much water so that he could move.
2- the technique has to be always the same when it comes to throwing the bottle, only changing it minimally to detect possible errors.
3- turning is essential. If you do not give the proper effect, the bottle never will be vertical.