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April 05, 2005
An excerpt from the SETPRO Instructor's Swing Training CD....
The following is a portion from approximately the 100 pages of information on the SETPRO Instructor's Swing Training CD.
Force, Torque, Momentum and Power, Basic physics of the swing.Part of the "mystery" surrounding swing mechanics is due for/no understanding of basic physical principles/properties such as force, mass, torque, momentum, and power.
These principles/properties are important because they help quantify our interaction with the physical world around us.
In terms of understanding how the body acquires and produces movement, motor learning researchers have look to other scientific disciplines such as physics and engineering.
The new theories of motor control that were first proposed in the 1960's and 1970's, and that form the focus for contemporary movement science research and literature review today. (Bernstein, 1967; Gibson, 1966; Kelso, 1984; Schmidt, 1975). Two current theories of motor control, the motor program theory and the dynamical systems theory, have both integrated concepts from the ecological theory of motor control into their constructs. Consequently, a new clinical intervention approach has evolved that advocates an "ecological model" of motor control. This new approach is called a task-oriented approach (Shumway-Cook & Woolacott, 2001).
A basic premise of ecological motor control it is that movement (how we learn to use our body) is determined by our interaction (how we deal with the constraints imposed upon us) with our environment. A large part of this interaction is dealing with the “physics” of ourselves and our environment.
Dealing with our environment is dealing with the following variables;
The gravitational field of the Earth.
Space (length, width height)
Time
Mass.
Newton's three laws form the starting point for basically all of classical mechanics. Classical mechanics being be understanding and application of how “macroscopic” object move in space and time. Macroscopic meaning that we are dealing with objects that we can see, touch, feel (as opposed to a comic and subatomic physics).
Newton's three laws simplified:
Here are Sir Isaac Newton's three laws of motion.
Law 1 - An object moving in a straight line will continue moving in a straight line, unless acted on by an outside force. Also, an object at rest will stay at rest. The word for this is inertia.
Law 2 - Force will cause a change in the motion of an object. The change in motion depends on the amount of force and the mass of the object. There is a formula for this F=ma (force equals mass times acceleration).
Law 3 - For each action, there is an equal and opposite reaction.Force
Most of us have an intuitive understanding of what force is. We know the heavy of the object the more effort it takes to move it. Which is a pretty good definition of “force”. Technically force is defined by Sir Isaac Newton's second law, Force= Mass x Acceleration (F=MA). Force is something that causes an object to move, and more specifically to accelerate (assuming there's no friction the object will continue to accelerate forever (until it approaches the speed of light that is)).
Muscles great force by a combination of electrical and chemical actions. These actions typically produce muscle contractions i.e. shortening of the muscle.
Units of force are typically pounds. As in example how much we way is typically specified in pounds (how much we way is the result of the Earth's gravitational attraction i.e. the acceleration of gravity acting upon our mass).
Which brings up another word/concept that people confuse, mass.
Mass
Mass is the property of an object that resists acceleration in a straight-line. How massive of an object is determined using Newton's second law Mass = Force/Acceleration.
Our weight is actually the measure of the Earth's gravitational attraction and is defined as Weight = Mass X Gravitational Attraction. Gravitational attraction is the property that the planet Earth exerts on objects which exhibit mass.
Inertia
Inertia is “first cousin” to mass. Inertia is the property of mass subjected to a rotational force and/or motion. Inertia en masse are not the same thing. Mass is a “prerequisite” for inertia, i.e. you cannot have inertia unless you have mass. But in her sure is the property of mass in a rotational “environment”.
Torque
If inertia is first cousin to mass, then torque is first cousin to force.
Torque is the most important concept to understand with respect to how the body swings the bat. The word torque is also the "scientific word" causing the most confusion with respect to understanding how the body swings the bat.Definition of torque: The torque on an object about some pivot point is due to the action of a force on the object.
Another way of defining torque is "force acting through a distance".
One of the most common applications of torque is force acting on a lever. That force is causing rotation around a fixed point i.e. the fulcrum of the lever. And the torque being created on one side of the fulcrum is being resisted by the torque created by the weight on the other side of the fulcrum (object you are trying to move with the lever).
In order for there to be meaningful torque, three things are required; force, distance, and a pivot point. The amount of torque produced is directly proportional to the force in the distance that that force acts through (length of the lever arm).
Centripetal Force
Centripetal force is a “poor cousin” to the concepts of inertia and torque. Centripetal force is poorly understood by most baseball people. And in fact most people refer to centripetal force as centrifugal force. And to the physicist there is no such thing as centrifugal force i.e. centrifugal force is an imaginary force “balancing” centripetal force.
The reason I call centripetal force a “poor cousin” is because it is a somewhat special form of force. Special and that it is “more passive” then your “ordinary force”. Centripetal force RESULTS whenever you try to constrain an object that wants to move in a straight-line to moving in curved line. And unlike “regular forces” which create energy by moving an object through a distance, centripetal force does not create energy any more energy than the object possessed prior to the centripetal force changing the direction of the object. This may sound somewhat confusing but simply stated centripetal force does nothing more than change the direction of an object that is already moving. And centripetal force does not affect the energy or power that that object had prior to centripetal force changing its direction. This is what makes centripetal force somewhat special i.e. it is purely reactionary (passive force if you will).
Centripetal force does have great influence on the swinging a bat IF the player can change the direction of the mass of the bat. The same principle behind the cracking of a weapon i.e. changing the direction of the mass of the whip (straight-line to rotation, rotation being created by the loop in the whip).
Posted by PaulNyman at April 5, 2005 12:27 PM