Loft is not necessary for backspin. One could drive a ball with a club having a vertical face and obtain much backspin and a good carry, provided the tee were high enough to allow the cut down across the ball, and it would have to be a really high tee.
Although the blow that produces backspin is a descending blow there is of course much more forward motion than downward at and about the moment of impact so that all the ordinary principles of the golf stroke are in the blow. The loft must get its chance to act as in any other stroke, but there must be no notion of leaving the loft to play the stroke for one unless one wants to be grievously disappointed.
I must return for a moment to one of Professor Thomson's statements that seems to me to be very interesting and to require some analysis: ". . . but if you grasp the principle that the action between the club and the ball depends only on their relative motion, and that it is the same whether we have the ball fixed and move the club or have the club fixed and project the ball against it, the main features are very easily understood."
I am now going to deal with what Professor Thomson meant to say. For this purpose let us take the case of an ordinary slice. We all know that a slice is produced by a glancing blow coming inwardly across the intended line of flight and Professor Thomson tells us that it is exactly the same whether we hit the ball with the club or fire the ball against the club. We must analyze this a little and see what results we get on paper before worrying about it any further.
Let us consider that we have played a perfectly good slice and that we did it by coming across the line at an angle of 35 degrees. Let us bolt our club down on the line quite rigidly at a right angle to it, as it was when we got our slice. Let us now fire our ball at the club down a line at an angle of 35 degrees to the face of the club.
Now most of us know enough elementary mechanics to know that in hitting a still object such as the face of a club, the ball will come off it at the same angle at which it hit it, that is to say that the angle of reflection will be the same as the angle of incidence, making a trifling allowance for the loft of the club. Here we have one object that is held absolutely still and all the motion is confined to the ball.
Now we must consider the other proposition, the case in which the club strikes the ball. The ball flattens onto the face of the club to a considerable extent and while it is thus in adhesion the two travel together for a short distance. This slice is being played, remember, in the same manner as the first stroke. While the ball and the club are adhering they travel together across the line from where the ball lay to the hole. In effect the club picks the ball up and carries it a little way inwards towards the player's side of the line of flight before the ball leaves the club. At the moment of impact there is no angular spread of the ball in any way. The same argument applies with possibly less force in the case of the ordinary drive where the point at issue is the "spread," or angle, of the ball after impact in a vertical plane instead of, as in the case we are considering, one that is almost horizontal.
The analysis that I have given of Professor Sir J. J. Thomson's famous lecture will show that this subject of the dynamics of the golf ball is not so simple that it may be dealt with successfully unless one, in addition to some knowledge of physics, also understands thoroughly the production of the various golf strokes.
In connection with the flight of the golf ball I am often asked to explain why the modern rubber-cored ball swerves so much more than the old gutta percha ball. This is supposed to be something in the nature of a puzzle but I believe the answer is simple. The modern ball on account of its greater resilience stays longer on the face of the club, although Mr. W. J. Travis, in Practical Golf says otherwise. It therefore has more time to be affected by the oblique nature of the stroke, and thus almost certainly has more spin than the old guttie had at the moment of leaving the ball. Every one knows that the swerve comes in mainly at the end of the flight of the ball. As the spin gets to work at approximately the same distance as it did with the guttie and the ball, from that point to the end of its carry, has a longer distance to travel the spin has a greater time within which to work its will on the ball. If we add to this Sir Ralph Payne-Gallwey's discovery about the defective center of gravity so prevalent in the modern ball and his experiments proving how it assists drift it is easy to see that there is quite enough to account for the apparently greater amount of swerve. In the main however it is a question of the longer carry giving the greater spin more time to act.
Before closing this chapter I (The Eight Way To Learn Golf) should like to suggest an experiment to any one who thinks that the beneficial backspin of golf is obtained by the loft of the driver as stated by Professor Thomson.
Prepare a block of wood or get a wall or other place fixed up so that it has the same angle as the loft. Against this fire a ball with a catapult or other instrument until you have ascertained the angle of rebound caused by the loft. Then at a yard or so, according to the force of rebound fix another piece of wood. Draw a mark round a golf ball so that it is a circle cutting both poles of the ball. Place the ball in the machine so that the circle is in the plane of its flight. Mark the top pole with a blue dot. Color the wall you are firing against red, or some color that will mark the ball. Deal similarly, but in a different color with the board that is to catch the rebound of the ball. Fire many balls at the first board and compare the distance on them between the mark left by the first board and that of the second. It seems to me that if this experiment were properly carried out one could accurately measure the amount of backspin produced by the loft alone in driving. It would be found to be very small. An arrow should be put on the circle round the ball showing the direction of the backspin, and care would have to be taken to fire the ball in such a manner that the arrow was correctly pointed. It seems to me that an absolutely correct measurement could be taken in this manner.