Magnus effect: Where is the energy coming from? I am not an expert in Physics, so please go easy on me.
The magnus effect creates a perpendicular force to the axis an object spins around and the velocity vector. But where does that energy come from?
Does the object loose energy by slowing down the spin or the velocity?
Every object that experiences the magnus effect looses velocity through friction, but does it loose considerably more energy than without spin (assumed the object is a sphere or a cylinder)?
 A: The Magnus effect , which applies to objects which have circular symmetry about the axis of spin, stems from the fact that the side of the object spinning towards the air flow (from forward motion) sees a higher air speed than the side spinning away from the direction of air flow. The thin layer of well-behaved (jargon: laminar) air becomes turbulent earlier on the faster side (jargon: it has a higher Reynolds number). Therefore, the turbulent wake behind the object is lopsided. This asymmetry leads to a tangential force. This phenomenon is not easily thought of in terms of energy. Yes, the object slows down and spins more slowly from drag but these only affect the forward speed and amount of tangential force respectively. I would guess that, yes, comparing objects with the same amount of kinetic energy to start but one has only translation kinetic energy while the other has translation AND rotation kinetic energy, the one with rotation will transfer more energy to the surrounding fluid. 
A: I'm not sure what you mean by "where does that energy come from?"  The Magnus force is a force not an energy. As the force  is at right angles to the motion, the Magnus force does no work, so no energy need come from anywhere.  
A: 
As shown in the figure, the water surface in a rotating bucket will eventually become concave. The faster the rotating speed, the more concave the water surface is. The bucket in the left picture does not rotate very fast, so the water surface is not concave very much. The bucket in the right picture rotates very fast, so the water surface is concave very much. CONCLUSION: The faster the water rotates, the lower the pressure in the center of the bucket.

As shown in the figure, because the air flow on the right side of the ball is opposite to the rotation direction of the ball, the air flow on the right side of the ball rotates slowly; the air flow on the left side of the ball rotates in the same direction as the rotation direction of the ball, so the air flow on the left side of the ball rotates fast. According to the conclusion about the bucket, the pressure on the left side of the ball must be lower than that on the right side of the ball. So the ball will be exerted a right-to-left force F.
