# The Role of Physics in Golf

## Introduction: The Golf Swing, Ball Flights, and Backspin

 Fig. 1: Ball Spin Diagram (Source Wikimedia Commons)

When swinging a golf club, there are a variety of factors in the mechanics of the swing that in turn influence the spin generated on the golf ball. This spin affects the flight the ball will take in the air. When a right-handed golfer's club-head trajectory impacts the ball on the inward side first then propels outward, this will create a counter clockwise spin on the golf-ball. [1] This counter clockwise spin causes the ball to move from right to left in the air. The degree to which the ball moves from right to left ultimately depends on how much spin was generated: more spin results in more ball flight movement. Golfers refer to this type of ball flight as a draw.

On the other hand, when a right-handed golfer's club-head trajectory impacts the impacts the outer side of the golf ball first then propels inward, a clockwise spin is generated on the ball. [1] This clockwise spin causes the ball to move from left to right in the air as seen in Fig. 1. Golfers refer to this ball flight as a slice or fade. This type of ball flight is more typical of an amateur golfer, since experts find that being able to have an inward swing is more difficult.

The third type of ball flight is simply a straight trajectory; however, this is the most difficult type of trajectory to consistently maintain. While one may think hitting the ball straight at the target would be the best option, the physics of the golf swing prove that relying on playing either a fade or a draw is a golfers best bet. In order to hit a straight shot, the golfer's club-head must hit the ball square in the center. In doing so, there is neither a clockwise or counterclockwise spin on the golf ball, which allows for a straight trajectory. However, there is a significantly smaller margin for error for a golfer trying to mimic this swing pattern than for a golfer attempting to hit a fade or draw. As a result, nearly all professional golfers rely on hitting either a draw, fade, or both.

Another type of spin that golfers use on the ball is backspin. Backspin is used by golfers to control the roll on the ball after it lands and helps golfers hit their balls closer to the hole. Backspin is generated when the bottom of the golf-head impacts the backside of the ball with a downward force. This contact causes the ball to compress, and the friction between the club head and ball results in the backward spin. The amount of downward force that is applied through the golf swing dictates the amount of spin on the ball.

## How Technology Affects the Game: Club-head Grooves and the Golf Ball

 Fig. 2: Smooth versus Dimpled Golf Balls. (Source: Wikimedia Commons)

The part of the golf club that has had the greatest impact on the amount of spin that can be generated on the golf ball is the club head grooves. [2] As mentioned earlier, spin is created from the friction between the club head and the ball upon impact. Grooves are used to create as dry a surface on the club at impact as possible by removing any water, grass, or dirt that may be interfering. In removing these factors, the grooves allow for the club and ball to create greater friction and in turn generate more spin. Recently, the USGA, the organization in charge of golf rules, decided to place greater restrictions on the amount of grooves allowed on club heads. Players had been using clubs with grooves deep enough that even when hitting balls out of the rough players were able to generate significant spin on their balls. The USGA felt shots out of the rough should be more penal, and they decided to limit the depth of grooves to essentially make the game more difficult.

Today, there are thousands of different types of golf balls that players choose to play with. Perhaps the most important element of the golf ball is the dimples on the outer shell. As seen in Fig. 2, dimples are extremely important for reducing the drag the ball has while in the air. This diagram further illustrates what happens with balls that only have dimples on either the right or left side of the ball along with a smooth dimple free surface on the other side. Balls with dimples only on the right hand side create counter clockwise spin after impact that causes the ball to move from right to left. [1] Further, dimpled golf balls are able to travel further due to the reduced levels of drag. Less drag allows dimpled balls to have greater lift and ultimately travel further.

## Conclusion

As anyone who has ever played the game can attest to, golf is one of the most difficult sports in the world. Though the objective of the game couldn't be simpler, mastering the physics of the swing and the multitude of factors involved is nearly impossible. It's not uncommon for a professional golfer to shoot a round of 62 one day and then shoot an 82 the next. Overall, from the swing itself down to the equipment, physics plays a tremendous role in the game of golf.

© Jay Fuster. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

## References

[1] T. P. Jorgensen, The Physics of Golf, 2nd Ed. (Springer, 1999).

[2] R. Minton, Golf by the Numbers (Johns Hopkins University Press, 2012).