# Question about Reverse Magnus Effect

• robhlee
In summary, the NASA guy was correct in his explanation of the maximum rpms allowed in the FoilSim App for middle school students, as higher rpms can create secondary boundary layers and decrease the lift force generated. Additionally, having a rough surface can negate the reverse Magnus effect and disrupt the linear relationship between rpm and lift force.
robhlee
Hi,
I was looking at the NASA website's FoilSim application (google it) and for spinning objects, there is a maximum rpm. I was wondering why there were maximum/restricted rpms, so I emailed a NASA guy with the question. He said that the FoilSim App was for middle school students and that higher rpms would create secondary boundary layers, or something like that, too complicated for middle schoolers. He also said that the rpm-lift force relationship remains linear (higher rpm-higher lift force) at higher rpms than allowed in the FoilSim. So then I read about the 'reverse Magnus effect', and now I need a bit of clarification. How would having a rough surface completely negate the reverse magnus effect (according to http://209.85.165.104/search?q=cache:5eXgtFXUgfkJ:maxwell.ucdavis.edu/~cole/phy9b/notes/fluids_ch3.pdf+reverse+magnus+effect&hl=en&ct=clnk&cd=1&gl=us) , and is the NASA guy mistaken when he told me the rpm-lift force relationship remains linear at increasing rpms?

Thanks.

Last edited by a moderator:
The reverse Magnus effect is a phenomenon that occurs when a spinning object moves through a fluid, such as air or water. It causes the object to experience a force that is opposite the direction of its spin. This force is known as lift force, and it is generated because of the differences in pressure that exist on the surface of the object due to its spin. The greater the spin rate, the greater the lift force generated. The NASA guy was correct in saying that higher rpm would create secondary boundary layers, or something like that, too complicated for middle schoolers. These secondary boundary layers are caused by the increased turbulence that occurs with higher spin rates. This turbulence can decrease the lift force generated, depending on the surface of the spinning object. If the surface of the object is rough, the turbulence will create eddies along the surface of the object, which will disrupt the flow of the fluid around the object, thus reducing the lift force generated. The NASA guy was also correct in saying that the rpm-lift force relationship remains linear at higher rpms than allowed in the FoilSim App. However, if the surface of the object is rough, the lift force generated will be reduced due to the eddies created by the turbulence. Therefore, the linear relationship between rpm and lift force will not hold true in this case.

## 1. What is the Reverse Magnus Effect?

The Reverse Magnus Effect is the phenomenon in which a spinning object experiences a force in the opposite direction of its spin. This is in contrast to the regular Magnus Effect, where a spinning object experiences a force in the same direction as its spin.

## 2. How does the Reverse Magnus Effect work?

The Reverse Magnus Effect is caused by the difference in air pressure on the opposite sides of a spinning object. As the object spins, the air on one side is moving in the same direction as the spin, while the air on the other side is moving against the spin. This creates a pressure difference, leading to a force in the opposite direction of the spin.

## 3. What are some real-world examples of the Reverse Magnus Effect?

The Reverse Magnus Effect can be observed in various sports, such as baseball, tennis, and golf. When a ball is hit or thrown with spin, it experiences a force in the opposite direction of its spin, causing it to curve in the air. It is also seen in the flight of frisbees and boomerangs.

## 4. How does the Reverse Magnus Effect impact flight?

The Reverse Magnus Effect can have a significant impact on the flight of projectiles. It can cause objects to curve or change direction, making it challenging to predict their trajectory. This effect is especially crucial in sports that require precise aiming or throwing, such as archery or discus throwing.

## 5. Can the Reverse Magnus Effect be useful?

Yes, the Reverse Magnus Effect can be intentionally used in sports such as football or soccer, where players can curve the ball to avoid defenders or make a shot. It is also utilized in some engineering designs, such as helicopter rotors and certain types of wind turbines.

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