Posted by: Mike Myers (mike.myers@bellnexxia.com) on Fri Apr 25 12:44:22 2003

Jack,
>
> I notice you differentiate forces applied from counter-rotating hands (you call torque) vs forces applied from the full rotating hand path (CHP):
>
> “With the aid of high-speed cameras, motion detectors, pressure sensors and a motion-study computer, it was found that there were two forces acting on the bat that generate bat-head acceleration (gravity is not supplied by the batter). One force transferred the body’s rotational energy by the angular displacement of the hands (termed - a circular-hand-path). The second force that accelerates the bat-head was torque (causing an object to rotate by forces applied from opposing direction). In the baseball swing, torque is mainly applied to the bat by the push/pull effect of the hands with a minimal amount supplied by wrist action.”
>
> This can be a source of confusion to anyone unfamiliar with your full discussion.
>
> Note: torque is a net force applied at 90 degrees to the axis of rotation. There is no requirement how this net force manifest i.e. two forces from opposing directions, as you suggest. This is why both forces you have identified are, in fact, torque examples.
>
> As the long as the object changed its angular speed, torque has been applied. For example, if you pull a lever, you have applied torque to the lever, although there is only one point of application.
>
> Regards,
> Mike.
>
> Hi Mike
>
> There is nothing contradictory between the definition you gave (“torque is a net force applied at 90 degrees to the axis of rotation”) and the explanation used on this site to define torque (forces from opposing directions that induce rotation). Both definitions require a net vector force working at 90 degrees to the axis arm.
>
> For an example, if you laid a bat on the floor and pushed on the knob with one finger (at 90 degrees to the shaft), the bat would rotate around a point. It would appear that a single force caused the rotation. But in fact there are other forces at work that must also be vectored into the equation – the inertia of the axis arm mass to acceleration, friction from the floor and air and etc. The vector sum of these forces is doing work in the opposite direction to the force applied by your finger. If the vectored sum of those forces were brought to zero, the bat would not rotate but move linearly. --- In the case of your “lever”, the hinge point is applying the opposing force.
>
> In the baseball swing, for reasons mentioned above, when you push on the knob-end of the bat with one hand (or in fact both hands), the knob would rotate around the bat-head. But that is not the result we want. We want the bat to rotate around a point close to the hands. This requires one hand to be pushing in one direction while the other hand pulls in the opposite direction.
>
> PS: If any of you coaches can think of a better descriptive than “Torque” for this push/pull action, I am open to suggestions. But in the meantime, I do not think teaching them “Quick Hands”, “Knob to the Ball”, or “Just Grip it and Rip it” will advance a hitters progress.
>
> Jack Mankin
>
>

Jack,

I completely agree that your torque definition is non-contradictory. However, as I indicated, the use of the term (by suggesting a requirement of 2 opposing forces)in your above discussion can be confusing. For example, the successive statements:

"One force transferred the body’s rotational energy by the angular displacement of the hands (termed - a circular-hand-path)."

"The second force that accelerates the bat-head was torque (causing an object to rotate by forces applied from opposing direction)."

True, however, one may conclude by implication, that your first force (CHP) was not torque, since you chose to explicitly call only the second force torque.

In reality, both forces are torque examples since in both cases applied forces are 90 degrees to an axis of rotation.

Keep up the good work. I enjoy the discussion.

Mike.