We have explained that forearm turning continues to add power even at the moment of impact. However, some observers believe that no additional power exists at the moment of impact. Using golf as an example, I would like to challenge this theory by delving into the mechanism of the swing.
Even though the arms are bent immediately before impact, in both golf (Figure 1) and badminton (Figure 2), the arms and equipment make a straight line at the moment of impact.
Recall the spin in figure skating. What happens when arms held close to the body (Figure 3a) are extended while spinning
(Figure 3b)? Rotation will slow down almost to a halt. This happens because the position allowing easy rotation is changed to a position where rotation is more difficult.
Based on this principle, rotations in badminton and golf will slow when the arm is extended, though not as much as in
skating.
You may respond that, when the racket or club is extended, the velocity at the tip should be increased.
That is correct. Figure 4 depicts a golf swing observed from above. Immediately before impact, the arm and the club make a straight line and can be supposed to rotate around a common pivot. The rotation velocities at the hand and the tip of the club are indicated as arrows. This drawing clearly illustrates that even if the hand velocity is slow, the speed at the tip is much faster.
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Figure 2:
An overhead'r·stroke in badminton
Slow
Clubhead ~Faster
Figure 4:
Immediately before impact in golf(Velocity increases
~Figure 1:
The moment of impact in a golf swinga b
Figure 3:
What if the arms are extended in a figure skating spin?toward the tip of the club.)
70. While the grip slows down, the clubhead speeds up ?
To continue the explanation in the previous section, it may be anticipated that even though the tip is accelerated, the grip is decelerated~ these speeds may offset each other and eventually slow down the velocity of the tip.
We made a rough estimate of how much the tip is accelerated.
Figure 1 shows a model where a driver, the longest of all clubs, swings in the sequence a ~ b ~ c. The motion involved
is examined through the model as indicated in Figure 2.
In actual swings, since the arms are alternatively bent and extended, it is difficult to determine length and weight.
Still, this model is a useful rough approximation of the situation. With this model it is relatively easy to calculate how tip velocity changes when the arm and the club make a straight line, as depicted in the uncocking process from
b ~c.
According to detailed calculations, the velocity of 100 in Figure 2b is halved at the grip and increased to 140 at the club tip in Figure 2c. These figures may vary slightly due to different assumptions, but will not show any great deviations.
A common piece of swinging advice is: "Accelerate to maximum velocity with uncocked wrists." But uncocking alone does not seem to accelerate the clubhead to any great extent. What contributes to maximum acceleration of the clubhead? There are two other factors involved: one is performed at the stage from a to b in Figure 2, the other is at the stage immediately before and after c. We will further look into these points in the following sections.
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b
0 <Impact>
c
Figure 1:
Swinging a golf driverAmt!J¢(£)9
....___::,
100
a. Overhead b. Immediately before uncocking
Privot
140
c. Immediately before impact The two sticks with attached weights represent the arm and club: the weight ratio of the arm to the club is 6 : 1; the length ratio of the arm to the club is 1 : 2. We assume that immediately after b, the arms are extended at once (uncocked).
Figure 2:
A simplified model of Figure 171. What is late hitting?
First, we will examine the stage from a to b of Figure 2 of the previous section,which is generally called the "downswing".
In order to produce a powerful shot, the body must be rotated quickly, and the power must be fully transmitted to the arms and club.
To accomplish this, you should increase rotational velocity during the downswing by decreasing the moment of inertia
(please refer to page 124).
To attain superb acceleration, it IS necessary to maintain a constant angle between the arm and the club until immediately before impact, to ensure that the body can easily accelerate, and to extend the arms and club.
Delay the downswing of the clubhead until the last moment befo re the impact, and smash the ball in a quick and powerful swing: this kind of swing is called "late hitting". The figure on the next page shows the exemplary form of a top professiona
l golfer, and provides us with an excellent model of late hitting.
The stage from b "* c of the previous model, which involves extending bent arms to make a straight line with the club, cannot be expected to produce much acceleration, as discussed above. Therefore, sufficient acceleration should be obtained before this stage. It is crucial to bend the arms and club adequately to reserve sufficient energy and accelerate body rotation.
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<What i s "" l a t e h i t t i n g " " ? >
In an actual swing, you can hit a powerful shot by reserving the energy up to Stage b, when the club becomes horizontally positioned, and then bj quickly swinging down. But if you wait too long,
the swing becomes delayed and will lose its effectiveness. By reserving an adequate amount of energy, you can maximize your own physical power.
72. Forearm turning to hit a ball hard!
Next, let's consider the stages immediately before and after impact (frame c on the previous page). How can we maximize clubhead acceleration and ball distance (even if 300 yards is a tall order ... )?
Figure 1 indicates a top professional's so-called "body-turn"
swing. Figure 2 depicts arm movements: both arms turn simultaneously, reversing their vertical locations.
Mental visualization of this technique is not enough; please attempt the movement indicated in Figure 2. Turn your forearm
(between the elbow and the wrist); this movement is called,
"rolling of the forearm".
In order to understand why this movement can accelerate the clubhead, hold a stick and turn the forearm as in Figure 3.
With this simple movement alone, the stick moves in a big arc with substantial acceleration. This is the principle of
powerful acceleration at the last stage, which has not yet been fully discussed.
Try this movement, using as much power as possible rather than decreasing power immediately before and after impact. If you maintain an unbent wrist, the ball should fly straight forward.
At any rate, to hit a ball more accurately and powerfully, replace relatively feeble wrists with the more powerful
"forearm turning" and rotation of the entire body. Additional new power will be imported at the moment of impact.
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Imagine hitting the ball with the
"follow-through".
Figure 1:
A golf swing that incorporates body turning and rolling of the forearm.Velocity: smaller
~
principle of forearm rolling
Velocity: