The Science of Why A Ball Curves
The friction between the spinning ball and the air causes the air molecules on the right side of the ball to move backward. ... If a ball is thrown with a counter-clockwise spin, it will curve towards the left. If it's thrown with a downward spin, then the ball will curve downwards.
Why do balls curve?
Philosophers have argued about this for hundreds of years. One reason for a non-uniform curve of a curveball is that at launch, the pitcher's hand naturally starts in the plane of the strike zone, while the batter's hands are in the plane of the pitch. The more likely that pitchers hit a strike, the higher the probability that the ball will curve downwards. This isn't a physics question, but the way we understand the idea of centripetal force is from our ability to move things with our feet (i.e. bicycles, bowling pins), so it's nice to know how centripetal force works to help the ball curve. Why does a ball curve? A slight head tilt A fair baseball will stay flat on a flat plate. But the ball isn't completely flat and can fit into the gap between the plates if its height is adjusted.
The physics of spin
The world around us is incredibly complex. Everywhere you go, the sun is shining, the breeze is blowing, the tree branches are swaying, there's a myriad of tiny particles swirling around all the time. We see this all the time, but it's not until you step back and look at the big picture that you begin to realize how intricate it really is. As you can see above, the air is a fluid that behaves pretty much like water. There are three main forces that govern the motion of air: gravity ... which pulls everything downward aerodynamics ... the physical laws that govern the way air moves heat conduction ...
The Magnus Effect
If a spinning ball hits a stationary flat surface, the ball leaves a mark called a shadow. But this ball shadow isn't a solid shadow. When the ball hits the ground, the friction created from hitting the ground releases a small amount of air and causes the air molecules to hit the surface of the ball. Since the ball is spinning, this tiny amount of air sends the ball shadow spiraling upwards with the ball. If the ball hits the same stationary surface on the opposite side of the ball, the shadow never reaches the ground. The spiral represents the ground, and it doesn't interact with gravity, and the shadow never falls back down. This can be seen in the shadow on the floor after a spinning ball has just hit it.