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What is the principle of banana ball in 2018 World Cup

Sihaiwang: banana ball is a technical term in football. Banana ball is also a highlight in the world cup. Some people associate banana ball with boat. What's the relationship between the two? You will know after reading this article.

What's the use of those four tall columns? Are they chimneys? Of course not. What do they have to do with banana balls in football?

It's also a ball. In fact, there are banana balls in table tennis, which is called spinning ball.

On the green field, banana balls are hard to kick out, but many people have played table tennis, and spinning balls have also been played, playing to the extreme, and even allowing the other side to fall because of misjudging the direction of the ball.

In physics, banana ball is a kind of 'Magnus effect'. To understand this effect, the simplest and crude way is to use another principle, Bernoulli's theorem.

Two balloons are placed in front of you. You don't treasure them. You blow them hard. It's reasonable that they should be blown away, but & hellip; & hellip;

But the two balloons are close together, because the air speed in the middle is faster when blowing from the two balloons, and Bernoulli's theorem says that the faster the flow speed is, the smaller the pressure is.

When the air pressure between the two balloons decreases, the normal atmospheric pressure around them forces them together.

So, what's the relationship between banana ball phenomenon and Bernoulli's theorem? The reason is that if you want to play banana ball, you have to make the football rotate. Let's start with an example of throwing a basketball from a high dam.

When the spinning basketball falls from the high dam, it flies far and wide horizontally because of the "banana ball" phenomenon.

When the ball is rotating, the movement direction of the sphere above the ball is opposite to the air flow direction. Due to the friction of the sphere, the air flow speed above the ball slows down, which will lead to the atmospheric pressure above.

Under the ball, the sphere moves in the same direction as the air flow. Due to the driving effect of the sphere, the air flow speed increases, resulting in low air pressure below.

Let's look at an example where the air flow is in the opposite direction.

It's not hard to analyze that if the air pressure at the bottom is big and the air pressure at the top is small, then the pressure will push the ball upward.

Football, tennis and table tennis, as long as they rotate fast enough, there will be a "banana ball" phenomenon on the green field.

From the above analysis, we can easily come to the conclusion that if you want to make the football fly to the left suddenly after a straight distance, then when you play the ball, you should start from the right bottom of the football, only in this way, the football can rotate left, that is to say, anticlockwise.

In short, left-handed, football to the left, right-handed, football to the right.

At the beginning of this paper, we mentioned the rotor ship, which uses the 'Magnus effect' to provide part of its power for the following reasons:

Sailboats are most suitable for downwind, while rotorcraft is most suitable for crosswind. The wind blows from top to bottom, and the rotor on the ship rotates counterclockwise, which causes the air pressure difference between the front and back of the rotor. The air pressure behind the rotor is greater than the air pressure in front, and the pressure acts on the rotor to push the ship forward.

To sum up, banana ball phenomenon is a Magnus effect. In order to understand this effect simply, we introduce Bernoulli theorem. However, we need to note that Magnus effect has a deeper explanation, but it involves turbulence, wake and boundary layer. It's easy to watch the ball, so we won't go further.