Balance Point
The balance point is the location on a bat where it may be supported and balance. It is needed to find the mass moment of inertia of the bat (MOI).
The balance point, center of gravity, or center of mass are terms used to describe a location on the bat where all of the mass would be concentrated if the bat had no volume. While it is often close to the geometric center of the bat, it does not have to be. The bat would lie horizontally balanced if it were supported only at its balance point. The location is reported in reference to either the knob end of the bat or the pivot point. The pivot point is 6 inches from the knob and will be described in more detail below.
The balance point can be readily found by balancing the bat on your finger. In this way one can observe the effect of knob or end loaded bats. A laboratory test, depicted in Fig. 5.1, provides a more accurate and repeatable measure of the balance point. The method is described in detail in ASTM F2398. The bat is placed in a fixture with supports that are 6 inches and 24 inches from the knob. The supports are placed on two scales. The weight from these scales (minus the weight of the fixture) W6, and W24, are used to find the balance point, BP, according to
(5.1)
where BP is with respect to the knob end of the bat. The balance point of a 34 inch long bat will typically be between 24 and 28 inches from the knob.
Fig. 5.1. Schematic of laboratory fixture to measure balance point of a bat.