Racquet Handle Weighting and Maneuverability
By Rod Cross
Inspection of 320 different racquets listed in the March 2004 and 2005 issues of RSI shows that almost every light racquet is head heavy and every heavy racquet is head light (see Fig. 1) This result is not so surprising because each racquet must have a comfortable swingweight. The swingweights in the RSI list vary over a relatively small range, from about 290 to about 340 kg·cm². Racquet weights themselves vary over a wider range, from about 240 to about 360 grams.
Figure 1: Balance vs. weight for
all 2004/5 performance racquets.
If you take a medium weight racquet (around 300 grams) and add 30 or 40 grams to the tip, it will feel really head heavy and will be very difficult to control. If you add 30 or 40 grams to the handle, the racquet will feel heavier but it will not be much more difficult to swing because the swingweight stays almost the same. The measured swingweight refers to rotation about an axis four inches from the butt end of the handle because that is how a racquet is swung in a swingweight machine. If all the extra weight was added at this axis, then the swingweight wouldn’t increase at all because the extra weight remains on the axis and no extra force is needed to rotate it around the axis.
Adding 30 or 40 grams to the handle does not increase the swingweight or the twistweight of a racquet and it does not increase racquet power. Racquet power increases when weight is added to the head, because that is where impacts occur. For the same reason, golf clubs and baseball bats concentrate weight in the head. However, most professional tennis players like extra weight in the handle because it makes the racquet feel more solid or more stable and easier to control.
The physics of “feel” and “control” are hard to pin down, but a simple explanation of the effect is as follows: Imagine that you are conducting an orchestra with a baton. If you hang onto the pointy end and wiggle it around, the heavy end will tend to stay where it is and the orchestra won’t have much of a clue what you are doing. But if you wiggle the heavy end, the pointy end will more or less follow what your hand is doing. Delicate wrist motion will add to the effect, enabling you to point the baton rapidly at one section of the orchestra and then another. That’s the principle behind handle weighting, but what are the physics of it?
A player swinging a racquet does not rotate it about a fixed axis, especially not the one used to measure swingweight. Just before the racquet hits the ball, in the last few inches of the swing, the racquet will be swinging about an axis that is somewhere beyond the end of the handle, not inside the handle itself. But the swing action starts well before that, when the racquet is back. The whole racquet is swung forward through a distance of about four or five feet and it covers that distance in a split second in a fast serve or groundstroke.
In order to get the whole racquet moving forward through four or five feet, a forward-directed force is needed on the handle. In addition, the racquet needs to be rotated through about 90 degrees in a forehand or backhand so it is pointing in the right direction on impact with the ball. The racquet starts off pointing approximately at the back fence at the start of the swing and is then swung through about 90 degrees to point approximately parallel to the net at the time of impact. The effort required to rotate the racquet is determined mainly by the swingweight about an axis somewhere beyond the end of the handle. That particular swingweight will be typically about double the measured swingweight. The extra 30 or 40 grams in the handle will make it slightly harder to rotate the racquet because the extra weight is swung around in an arc centered beyond the end of the handle.
There are two separate actions required to swing a racquet forward, although each is performed at the same time and it might therefore appear to be only one action. One is the action needed to move the whole racquet forward. That is done by pulling or pushing the handle forward. The other is the action required to rotate the racquet. That is done by applying a torque or twisting action to the handle, in the same way that a steering wheel or door handle is rotated. The effect of extra weight in the handle can best be explained by looking at these two actions separately.
|Figure 2: A force applied at right angles to a racquet acts to move the racquet sideways. If the force acts at the balance point as in (a), the racquet moves forward without rotation. If the force is applied at the handle, as in (b), the racquet moves forward but the racquet head rotates backward with respect to the handle. Extra weight in the handle reduces this backward rotation effect.|
Suppose that a force is applied at right angles to the handle of a racquet, as shown in Fig. 2. If the force is applied at the balance point, then the whole racquet will move forward without rotation. However, players push forward on the handle, not at the balance point, in which case the whole racquet moves forward and it also rotates. If the handle is relatively light, the handle will move forward rapidly and the head will get left behind. In fact, the head will move backward due to rotation of the whole racquet unless the player also exerts a torque on the handle to rotate the head forward. If the handle is relatively heavy, the handle will not move forward as rapidly and the head won’t fall so far behind. The player will still need to exert a torque to rotate the head forward, but the required torque will be less than that required with a light handle. This is the big advantage of having a heavy handle.
There is an additional reason why handle weighting works to reduce backward rotation of the head. Weight in the handle shifts the balance point closer to the butt and it also increases the racquet’s resistance to rotation. The torque on the handle due to the push force is therefore reduced because the force acts at a point closer to the balance point. If the force acted at the balance point, the torque would be zero and the racquet wouldn’t rotate at all. The combined effect of the reduced torque and the increased resistance to rotation means that a player can push forward as hard as he or she likes on the handle without the head falling too far behind.
A social player doesn’t need a heavy handle because he doesn’t swing his racquet as fast as a professional player. Consequently, the social player doesn’t suffer as much from having the head lagging behind, and can easily rotate the head forward using a small torque on the handle.
|Figure 3: Backward rotation of the racquet head must be prevented by applying a torque to the handle using the wrist in such a way that Force A (near the first finger) is bigger than force B (near the little finger).|
In order to rotate a racquet forward, a player must exert opposite forces at different parts of the handle (Fig. 3). This is a perfectly natural, subconscious action that results whenever a player swings a racquet. Without this action, the racquet head would fall behind as soon as the player pushed forward on the handle. Exactly the same action is required when holding a racquet (or any other object) steady in a horizontal position. The area of the hand near the first finger pushes up on the handle and the base of the hand near the little finger pushes down on the butt end. At the start of the swing of a racquet the wrist needs to be locked to pull the head around. With a limp or completely relaxed wrist, there would be no torque applied to the handle and the head would fall behind. When a torque is being applied at the start of a swing, the muscles in the forearm and wrist tense up and the force exerted on the handle near the first finger increases rapidly.
The torque required to rotate a racquet depends on the swingweight of the racquet and also on the speed at which the player wants or needs to rotate the racquet. Keeping the wrist locked at the start of the swing helps to swing the head around, but once the racquet is rotating, keeping the wrist locked can actually slow down the subsequent rotation speed. For that reason, top players usually relax the wrist just before impact, ending up with a “wristy” swing. Golf players do the same thing. They start off with the wrist cocked so that the club is at right angles to the forearm at the start of the swing. Just before impact the wrist is relaxed, the club swings around rapidly pulling the hand and wrist around with it, so the club and forearm are in line at the time of impact with the ball. The club or racquet rotates most rapidly just before impact, despite the relaxed wrist, for an interesting reason. That is, the forearm slows down just before impact. That way, rotational energy in the forearm is transferred to the club or racquet, just where the player wants it. By slowing the forearm, a backward force is exerted on the handle and the head swings around rapidly. It is the opposite effect of that shown in Fig. 2 where the head falls behind if the handle is pushed forward.
Having extra weight in the handle therefore allows a top player to control what he is doing. It slows down the forward motion of the handle and the backward motion of the head just enough so that he can swing the head around with a reasonable effort rather than an excessive amount of wrist torque. An average player doesn’t need extra weight in the handle because he doesn’t swing the handle forward fast enough for it to present a problem. Similarly, he doesn’t need to apply a large torque to rotate the racquet since he doesn’t rotate the racquet as fast as a pro. A recreational player needs to get the same power as a pro does from his racquet, so there must be the same weight in the head, but there is no need for a heavy handle. That’s why almost every light racquet is head heavy and every heavy racquet is head light.
See all articles by Rod Cross
About the Author
Rod Cross retired in 2003 as an honorary member of the Sydney University staff and continues to work on the physics of sport and forensic physics. He is a physicist and co-author of The Physics and Technology of Tennis available from the USRSA.
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