For Teaching Young Players who are Learning how to Throw!
A Physics discussion related to throwing....
While you can find article after article that break down every scientific nuance of throwing / pitching, I'm going to keep it simple a use a few simple examples of what we are trying to achieve. In fact, I read articles that speak with authority and having pitched myself, I'm not so sure they know what they are talking about or how they are helping anyone. Our bodies are complex systems with many many degrees of freedom. Watch any major league throw and think about the number of joints, muscles, ligaments and tendons that are engaged throughout this complex body motion. This is complicated stuff! To understand how I thinking of throwing, consider the following devices with fewer degrees of freedom.
Now while creating rotational velocity from the legs and torso is heavily stressed above, obviously the arm does some work too. I compare this to when you pushed your friend on a big wheel when you were a kid...you're legs were running pushing that thing as fast as you could go, but you were still able to give that final twitch/push when you sent him hurling ahead towards whatever danger awaited ahead. The arm (and fingers) act in that way. The arm must accept the rotation velocity and build on top of this, just like the final shove of the big wheel. Now, examine this major league throw and visualize the rotational forces at play. A throw is sequence of events that maximize the velocity of the ball by way of rotational force generated by the legs and torso, constrained by the body's degrees of freedom. I see something that has elements of the finger propeller and the trebuchet in the sequence below.
Image from M&R Glasgow: https://www.flickr.com/photos/glasgows/131547232/in/photostream/
The human arm alone still has multiple degrees of freedom, but it alone can not create powerful throw by itself. The arm can push things, it can pull things, it can snap a forearm wrist and fingers, but it needs a body to maximize its velocity. The arm can't create a powerful rotational force. Try it, how fast can you move your arm without anything else? A proper throw is a sequence of events that maximize the velocity of the ball by way of rotational forces generated by the torso and legs, constrained by the body's degrees of freedom.
The finger propeller is a simple device that transfers rotational velocity applied to the stick (sort of like a torso) to a stiff propellor (like an arm). By doing so, the propellor moves so fast this device will fly. It has few degrees of freedom. A baseball throw is similar in that the legs and torso maximize rotational velocity which translates to arm velocity (like the propellor). There are many obvious difference, most notably that the propeller is rigid and stiff. A torso does not have a giant pair of hands spinning it, this it must create velocity using legs and itself. The rotation axis of a throw is not vertical.
Baseball Throw 101
The Trebuchet. A midevil device of fear, death and destruction. The trebuchet creates tremendous rotational forces such that it can hurl boulders long distances. It uses a stiff arm that rotates horizontally to the ground to maximize the rotational velocity of a payload at the end of a loose non-rigid rope. There are obvious difference between a trebuchet and a throw. It has fewer degrees of freedom. An arm is not like a loose rope. A throw is not a rotation that is completely horizontal to the ground. But much like the propeller, the payload is pulled and accelerated from core rotation, much like the body must accelerate a throwing arm.