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The Effect of Mass and of Swingweight
More mass is definitely better. More swingweight (moment of inertia) is also definitely better. The touring pros, in customizing their racquets, add mass and increase swingweight, because they know from personal experience what really works. Their customized racquets bite on the ball more, so they are able to generate heavy spin on their [Devi essere iscritto e connesso per vedere questo link] and [Devi essere iscritto e connesso per vedere questo link]. Pete Sampras' heavily customized Wilson Pro Staff 85 (a modification of the legendary St. Vincent ProStaff, which is no longer in production) weighs 14 ounces, about the same as the old woodies, but much heavier than the heaviest racquets marketed to the public these days.
Chain store customers, and even those who buy at pro shops, demand lighter racquets -- completely the opposite of the pros! A candid observer must find it somewhat incredible that even though the racquet makers pay the pros lots of money to display what appears to be the same racquet they are selling to consumers, in reality the racquet is not at all the same in weight or swingweight. Racquet manufacturers tout light weight as if it were something good, when in fact they should be putting a warning label on their racquets advising buyers that they are increasing their risk of disabling injury if they insist on banging away with a wimp stick. The heavier, the better. If 14 ounces sounds big to you, consider that even ladies and juniors used to play with wood racquets that weighed that much, and Don Budge won the Grand Slam with a racquet that weighed a whole pound.
Mass (in kilograms, symbol M) is a measure of the racquet's "inertia," a word that means essentially its resistance to change. The change resisted by mass is change in linear (straight-line) velocity. More mass means that the racquet will not slow down so much on impact. A short, controlled swing of a heavyweight racquet can hit the ball harder than a frantic flail of a featherweight. Same as bats in baseball: if you want home run power, bring a heavy bat to the plate. Babe Ruth's long bat weighed 52 ounces. You want a racquet that will hit through the ball, instead of bouncing off. Pete Sampras' second serve has an [Devi essere iscritto e connesso per vedere questo link] on it because his racquet can bite on the ball due to its high inertia on contact.
Mass is not the same thing as weight, but weight units such as ounces may readily be converted into mass units of kilograms, using the conversion factor of 1 ounce = 0.02835 kg.
Swingweight (symbol I) is another measure of the racquet's inertia, but it is a different kind -- rotational inertia, or a resistance to change in a racquet's angular velocity about an axis of rotation. A useful way to understand swingweight is as the energy storage potential of a racquet. Just like flywheels, racquets store up the player's effort. A racquet with a high swingweight (I in the formulas) requires more effort to swing, but will not lose much angular velocity on impact, and will snap through the ball more, biting for more spin, especially if the strings are tight and the head is small.It is most important to realize that swingweight has meaning only with respect to a specified [Devi essere iscritto e connesso per vedere questo link]. A swingweight number where you don't know the axis of rotation is of no use. The published swingweight numbers of the USRSA come from measurements on their Babolat Racquet Diagnostic Center (RDC), which measures swingweight about an axis of rotation 10 cm from the handle end. In play, this is not the axis of rotation of the racquet, so you will have to use the [Devi essere iscritto e connesso per vedere questo link] to convert the RDC swingweight figure to a value for I that can be used in the formulas.
Angular velocity means how much of a circle is swept out every second, in radians per second. There are 2p radians in a circle so an object having an angular velocity of 6.28 radians/s will rotate at one revolution per second.
On the forehand, the axis of rotation is 7 cm from the handle end, which is between the ring and middle fingers. Hold a racquet and waggle it to see that this is true. On the serve, where most top players use a choked-down grip over the butt cap, the swingweight will be higher because the axis of rotation has moved to 5 cm from the handle end. In other words, swingweight will change depending on how low you grip the racquet. Notice when Pete Sampras is going for a forehand putaway, he chokes way down over the butt cap to increase the swingweight.
The unit of measurement of swingweight in tennis is kg.cm2 (kilograms times centimeters squared), which is the unit for the swingweight measurements of the Babolat Racquet Diagnostic Center (RDC), presently the industry standard measuring device. Other scientific names for swingweight are moment of inertia, rotational inertia, and Second Moment. More swingweight is good for accuracy and comfort (low Torque, Shock, Shoulder Crunch, and Elbow Crunch).
A racquet with a high swingweight takes more effort to whip around the axis of rotation, but on impact that investment pays off in better speed and accuracy. "Maneuverable" is a term loosely used to describe a racquet with a low swingweight (although there seems to be some confusion between swingweight and Moment as this term is used). Maneuverability in a racquet, under this definition, is not good, because high swingweight is good.
Two racquets that weigh the same (have the same mass) may have very different swingweights because of the way this mass is distributed. More mass to the head of the racquet, such as by adding lead tape, will increase swingweight. Although more swingweight is good, head-heavy balance is bad for your arm, so lead head tape fixes one problem (higher I) but aggravates another (higher r). Increasing r means a higher Shock, Torque, Moment, Work, Shoulder Pull, Shoulder Crunch, Wrist Crunch, and Elbow Crunch. Note that the effect of r is squared in the Shock and Torque formulas, but the effect of I is not. So lead tape to the head should be counterbalanced somehow with a tailweight. The tailweight will not affect the swingweight materially because it will be close to the axis of rotation.
una decina nel manico? 
