First off, some background. The Magnus Effect is the phenomenon of a spinning object flying in a fluid (air) experiencing a force perpendicular to the line of motion in which it's flying. As in Figure 1 below, the ball spinning like a fastball or dropball causes the air at velocity V to travel
a little bit faster than V underneath the ball, and a little bit slower than V on top of the ball, causing a difference in pressure. And in accordance to the Bernoulli Principle (google it!), the side of the ball in which the air is traveling slower will experience more pressure than the side with the faster moving air. Thus, the resulting force F will be in the direction of the side with least pressure, the ball drops.
Figure 1: The Magnus Effect on a spinning ball. V is the air's initial velocity, more lines underneath the ball indicate the increase in the air's velocity, and hence less pressure. F is the resultant Magnus force towards the side of least pressure. Ok, so we know that a ball that has topspin will go down, and a ball that has backspin will stay up. But, what about side to side curveballs and screwballs? The Magnus Effect is not exclusive to the vertical direction, but as far as the limitations of humans are concerned, it's impossible to throw a true curveball or screwball with complete horizontal spin. No matter what, the ball will always have a tilted axis of rotation, this is because your hand is always going to be either under or over the ball. It is impossible for your hand to be completely on the side of the ball to spin it. Therefore, most screwballs and curveballs you see are riseballs or dropballs that have some component of side spin making the ball move in or out. What makes the ball go side to side is how much pressure you apply to one side of the ball. Like pushing a big box across the floor, the only way to push the box straight is to push from directly behind it. Pushing just a little off to the side, will make the box turn or spin.
But even with all these fancy terms and differences in air pressure, we cannot forget about the principle force gravity. The forces on the ball due to gravity greatly outweighs the effects of the forces from the Magnus Effect. Gravity is a powerful thing, it acts on all objects all the time, and accelerates them at 9.8 m/s2 or 32 ft/s2. In fact, ignoring the forces from air pressure, if a pitcher were to throw a pitch at 65 mph from a 37ft release point, by the time it gets to the plate, the ball would drop a total of 29 inches! This is why pitchers must throw the ball upwards to compensate for the drop from gravity so the ball ends up in the strike zone. See Figure 2, the green line always has an upward angle regardless of pitch.
Basically spin can be thought to help or hinder gravity, changing the ball's path just enough to make hitters miss. Dropball spin helps gravity, the ball drop a little bit faster than a fastball would, hence hitters generally swing over them and ground out. Riseball spin hinders gravity, the ball drops a little bit slower than a fastball would, and hitters swing under them and pop up. Take a look at Figure 2, from top to bottom, the pitches are: 1. Fastball 2. Roll drop 3. High Rise 4. Strike Rise 5. Low Rise. The red dots are the path of the ball. As you can see compared to the fastball, the drop has a steeper descent. The strike rise which is aimed higher is not quite on its way down because the upward spin is hindering gravity, making the ball plateau slightly at the top of its flight path. The low rise is aimed lower, and if you look closely it's actually going down.
Figure 2. From top to bottom: Fastball, Roll drop, High Rise, Strike Rise, Low Rise. The red dots are the actual path of the ball, the green line how the ball would travel without gravity, the blue lines are the strike zone. Along with affecting the movement of the pitch, spin also affects the speed of the pitch. Dropballs are always faster than riseballs for the following reasons: The vector addition of the forces on the ball, a larger radius of circular motion, and the amount of force by the pitcher's fingers in the direction of horizontal motion.
Forces and velocities are vector quantities, or they have direction. If two forces are in the same direction, they are added and the ball speeds up, opposite direction, they are subtracted and the ball slows down. When all the force vectors in all directions on an object are added through vector addition (google it!), an overall velocity can be determined. In our case, once the ball leaves the pitcher's hand, the only forces acting on a pitch are gravity and the Magnus force from the spin. Adding these forces will give us the acceleration and velocity in the vertical direction, then adding the initital horizontal velocity using vector addition, we can determine the overall velocity of the pitch. Therefore, since riseball spin produces a force opposite of gravity, a riseball is traveling in the downward direction at a slower velocity than a dropball. So if we assume the same horizontal velocity for a riseball and dropball, through vector addition we can conclude that the overall net velocity for a riseball will be slower.
Try thinking of vector addition like this. Imagine a North, South, East and West coordinate system drawn on a table. A ball is rolled from one end of the table towards the North. As the ball is rolling, it is nudged slightly from the South-West. As you can imagine, the ball changes direction slightly to the North-East, but it also speeds up. If the same ball traveling North were nudged from the North-East, the ball would change to a more North-West direction, but it would also slow down.
The velocity of an object traveling in a circle is directly proportional to the radius of the path it is traveling. So, the larger the radius of the circle, the pitcher's arm, the faster the ball is going at the point of release. When throwing a dropball, the pitcher releases the ball off of her fingertips with her wrist straight to make the ball have topspin. To throw a riseball, the pitcher must get her hand underneath the ball to create backspin, so her wrist is in a bent position at release, a shorter radius of motion. This bent position versus the straight position of the wrist can be the difference of a couple miles per hour.
Note: If you want to know more about wrist position for different pitches, go talk to a pitcher! Talking to pitchers is a good way to learn more about spins as well. Know how the ball spins, know where it's going, know how to hit it.
Finally, a last contributing factor to the speed of the pitch is how much force you apply to the ball in the direction of motion, the plate. Like the earlier box analogy, if you push from directly behind the box, all your force will be used to push the box in the direction you want to go. Any force a little off of centre will cause the box to turn, you have to push harder to slide the box the same distance as the box that slid perfectly straight. When throwing a peel drop, your hand is completely behind the ball spinning it downwards. For a riseball, all your force is applied underneath the ball on the seam to make it spin in the opposite direction. Again, if you can't understand me, go talk to a pitcher.
So what does this all mean? Well from the earlier 5 questions we can use the spin we see to make an adjustment with our hands to hit the ball square. For those hitters who can't see spin, they are put at a disadvantage because their eyes can only recognize the height of the ball. They then swing to where they assume the ball to end up, however if the ball is spinning in a different direction they might miss. Good pitchers are able to throw the ball that is able to spin up or down, as well as have some component of side spin, a curve rise, or a screw drop for example.
Also, as discussed earlier riseballs are slower than dropballs, therefore you should have more time to hit it right? This is not necessarily true, although the ball is moving slower through the hitting zone, as far as reaction time is concerned you actually have less time to hit a riseball than a dropball. Remember, the golden rule says that higher pitches must be hit more out front, lower pitches farther back in your stance. So, for the simple fact that you must hit a high inside riseball approximately 2 feet farther out in front than that of a low outside dropball, the less distance traveled by the ball provides an illusion of increased velocity. The less distance the ball travels, means there is less time to react, an equivilant to an increase in speed. In fact, if a riseball were to be thrown at 65mph high and inside, you would have to have a quicker reaction time of .021sec, equivilant to an increase in speed of 4mph.
