The Knuckle Ball

The description of how the Knuckle Ball(A soccer move where you try to kick the ball with the least amount of spin to create an unpredictable movement)With a example of it using coding an animation/game about it with a leg demo/entertainment/visual
Daniel Khan Odai Sawedi
Grade 6

Problem

Our problem is that we do not understand how the knuckleball works, so we made a question: How do you do the knuckleball, and why does it move so unpredictably?

Method

First we had to do lots of research for our explanation. After we had to make a demo. The following are the steps for the demo:

1. Shape the cardboard.

2. Glue the cardboard  together.

3. Make the stand.

4. Put the soccer cleat onto the leg.(optional)

5. Make the pulley system.

6. Test and debug. 

 

Research

To shoot a knuckleball, you need to kick the ball with very little spin. If too much spin comes in, the knuckleball effect will not be completed. Let’s first talk about the case where you do spin the ball. To get the ball to spin, we need to put torque into the ball which is equal to the force applied. Multiply that by the perpendicular distance (the shortest distance between a point and a line or surface, measured along a line that is at a right angle to the given line or surface) from the soccer ball’s centre of mass. With the knuckleball, we want to kick the ball in such a way that we apply no torque to the ball. So to shoot the knuckleball, your foot has to move in a line of motion that goes through the center of mass of the ball. But that doesn’t explain why the ball moves in such an irregular pattern. To find this out, we need to look at a subject of science called fluid dynamics.

Fluid Dynamics is the study of how fluids interact with moving objects (air is a fluid, a soccer ball is an object). The knuckleball is also used in baseball. People used to think that the seams on the baseball jutted out and caused turbulence in the air behind the ball making the ball suddenly change direction, but this idea had one major contradiction. Where are the seams on a soccer ball? In fact, in the 2010 World Cup, Adidas released the Jabulani. A perfectly spherical ball. The funny thing is that the Jabulani was the most out of control, overpowered ball for knuckleballs. Before I continue, there are two terms we will need to know. Laminar flow, and turbulent flow. Laminar flow is when a fluid flows smoothly around an object, while turbulent flow is a chaotic process where the flow around the object results in sudden changes within velocity and pressure. Researchers have learned that something very interesting happens at a point called the drag crisis. The drag crisis happens when the drag force for the ball drops dramatically, which results in an increase in speed. 

The drag crisis does sound unnatural, but there is a simple explanation. When the drag crisis happens, the flow of air around the ball is going from laminar to turbulent, resulting in the sudden decrease in drag force. We can understand more about the knuckle effect from the boundary layer theory. A boundary layer is the thin film of air which encases a moving object. This is why your car is still dusty even after driving it. The boundary layer is subject to intermittent reattachment (when something is temporarily disconnected and then reconnected multiple times) to the ball. This gives the ball a side with laminar flow, and a side with turbulent flow. The side pattern is random, so any side can be laminar or turbulent at any given moment the ball is in the air. This means that the constant detachment and reattachment of the boundary layer which makes the random turbulence on any side of the ball is the main reason of the knuckle effect. In conclusion, the drag crisis phenomenon is the main reason that a knuckleball happens, switching between a turbulent and laminar flow of air creating the unpredictable shooting technique.

 

Data

To shoot a knuckleball, you need to kick the ball with very little spin. If too much spin comes in, the knuckleball effect will not be completed. Let’s first talk about the case where you do spin the ball. To get the ball to spin, we need to put torque into the ball which is equal to the force applied. Multiply that by the perpendicular distance (the shortest distance between a point and a line or surface, measured along a line that is at a right angle to the given line or surface) from the soccer ball’s centre of mass. With the knuckleball, we want to kick the ball in such a way that we apply no torque to the ball. So to shoot the knuckleball, your foot has to move in a line of motion that goes through the center of mass of the ball. But that doesn’t explain why the ball moves in such an irregular pattern. To find this out, we need to look at a subject of science called fluid dynamics.

Fluid Dynamics is the study of how fluids interact with moving objects (air is a fluid, a soccer ball is an object). The knuckleball is also used in baseball. People used to think that the seams on the baseball jutted out and caused turbulence in the air behind the ball making the ball suddenly change direction, but this idea had one major contradiction. Where are the seams on a soccer ball? In fact, in the 2010 World Cup, Adidas released the Jabulani. A perfectly spherical ball. The funny thing is that the Jabulani was the most out of control, overpowered ball for knuckleballs. Before I continue, there are two terms we will need to know. Laminar flow, and turbulent flow. Laminar flow is when a fluid flows smoothly around an object, while turbulent flow is a chaotic process where the flow around the object results in sudden changes within velocity and pressure. Researchers have learned that something very interesting happens at a point called the drag crisis. The drag crisis happens when the drag force for the ball drops dramatically, which results in an increase in speed. 

The drag crisis does sound unnatural, but there is a simple explanation. When the drag crisis happens, the flow of air around the ball is going from laminar to turbulent, resulting in the sudden decrease in drag force. We can understand more about the knuckle effect from the boundary layer theory. A boundary layer is the thin film of air which encases a moving object. This is why your car is still dusty even after driving it. The boundary layer is subject to intermittent reattachment (when something is temporarily disconnected and then reconnected multiple times) to the ball. This gives the ball a side with laminar flow, and a side with turbulent flow. The side pattern is random, so any side can be laminar or turbulent at any given moment the ball is in the air. This means that the constant detachment and reattachment of the boundary layer which makes the random turbulence on any side of the ball is the main reason of the knuckle effect. In conclusion, the drag crisis phenomenon is the main reason that a knuckleball happens, switching between a turbulent and laminar flow of air creating the unpredictable shooting technique.

 

 

Conclusion

 In conclusion, the drag crisis phenomenon is the main reason that a knuckleball happens, switching between a turbulent and laminar flow of air creating the unpredictable shooting technique.

 

Citations


 

Acknowledgement