Static moment situation in a racquet looks similar to this pic:
For this example I used the situation where you add 4 g to the tip and 10 g to the butt. All is idealistic (perfect tip, perfect butt placements of mass). And as the centre point of hand holding the racquet I used 9 cm (never mind if this is 7, 8, or 9.5 cm in reality, it doesn't change much in terms of a principle).
Any added mass creates another static moment, and differential static moment equals (mass added) * (length between added mass position and the fixed point). The fixed point is center of your hand holding the racquet. Any moment tends to rotate the racquet around the axis in fixed point. The further the mass from this fixed point is, the bigger the moment (force) to rotate (linearly proportional). It feels in hand as a heaviness.
So, any mass added in direction closer to the tip when looking from the center point of hand increases static moment of a racquets. But also, any mass added in direction towards the butt when looking from the center point of hand also creates the differential moment opposite to racquets, moment, therefore it decreases the static moment of the racquet.
The differential moment is equal to the formula in rectangule (delta M = M1 - M2). delta M adds to the M(racquet). M1 = 4 g * 59.6 cm. M2 = 10 g * 9 cm. M1 and M2 act in opposed directions (circles). M1 acts in direction of racquets static moment, so it inreases it in fact. M2 acts in direction opposed to racquet's static moment, so actually it decreases it a bit.
M is a vector, so it must be observed as such. While mass or swing weigth are scalars.
Moment (static moment) of a racquet is what you feel in your hand as head heaviness when you hold your racquet still by the handle (with playing hand only). Whenever you feel racquet a head heavy, you feel racquets static moment. The bigger the static moment of a racquet, the heavier the feel when racquet is held still. The smaller the static moment of a racquet, the lighter the feel in your hand.
It is not directly proportional to balance point (COM) of racquet, although head lighter racquets should have smaller static moment too, and vice versa. Sometimes you have head light racquets which feel quite head heavy, more than their balance should actually suggest. This is because of their higher inherent static moment.
Static moment influences a bit of swing dynamics too, and a bit of racquets behaviour too. Because even in swing, static moment is present, so there is some additional effort needed by the hand to compensate it.
And also, physical formula states that:
Torsion = Moment * Torque. Therefore, the bigger the moment, the higher the torsional force. So it affects even impact with the ball.
Now, I don't yet have a picture, but imagine adding a leather grip instead of adding 10 grams to the butt. Let's suppose for example that this leather grip is 10 grams heavier than the original grip, so we actually add the same mass to the handle if we replace original grip with leather grip.
What happens to the moment? The additional weigth of a leather grip is evenly distributed throughout the whole handle part which the grip covers. Let's suppose that this length is 18 cm. So, in this given example, exactly one half of the leather grip is in direction to the butt from the center point of hand, while the other half is in direction of the tip. And if the mass is evenly distributed, than one half of leather grip creates the moment which completely cancels the moment created by the other half of the grip, because they act in opposed directions!
Therefore delta M is equal to mass added to the tip * 59.6 cm. Static moment only increased, while adding a leather grip didn't help to cancel some of the moment at all! This is quite contrary to adding some mass to the butt, which did create moment of 10 g * 9 cm to cancel at least one part of the racquet's moment.
This is the reason why adding mass near the butt is simply superior to adding leather grip. It helps in creating lower static moment of a racquet - this means it helps in creating a racquet that feels more head light, expressed in terms of experience. It's also a bit better at moving of the balance point more to a more head light balance too (because of placement of mass which is more distant to COM than average distance of added leather grip mass).
Now in terms of swing dinamycs, for what I know, moving a balance point more to HL helps some. But I experience that with mass added to the butt racquet just feels whippier compared to adding a heavier grip which makes swing feel more sluggish. I don't know yet how to explain this by physics, yet I'm certain with this experience.
I hope some will appreciate this effort to explain this
for some reason static moment of a racquet is a spec that is never taken into account and which is never measured. Unimportant? Judge for yourself.
