Historically, the golf swing has always been part art, part athleticism and part science. The way the swing has been taught over the years has varied the emphasis on these three areas, but with all the technological advancements in the game in recent years, the modern swing is more science than anything else. A rudimentary understanding of physics will serve every level of golfer well when trying to optimize each motion in the swing. Four elements in the golf swing are of particular value.
Imagine swinging a heavy bucket of water with your arm. Swing it smoothly back and forth with a fully extended arm, and the centrifugal force of the swing with keep the water in the bucket. Try to start that swing with your fingers, hand or elbow and the bucket will jerk and become unbalanced, spilling water all over the place. The same principal applies to the golf swing. Keep your forward arm straight through the swing and feel the clubhead as the heaviest part of the club–with a force extending out away from your shoulder through your arm–and the clubhead will return smoothly at the same level where it started. This is exactly the position you want to be in at impact.
If the fastest moment of your golf swing–the point at which the clubhead is moving fastest–is just beyond the ball at impact, your clubhead must be accelerating through the ball. This is exactly the condition you want to repeat every time. This accelerating motion imparts a positive spin on the ball, making it travel exactly along the line you intend. The opposite condition of negative acceleration--deceleration--brings the clubhead through as it is losing speed, meaning the clubhead is changing angles through impact. The ball will lose spin quickly and be subject to all sorts of unpredictable forces like wind.
This is a particularly important aspect of the golf swing with today's modern, large headed drivers. When the ball is on a tee, your driver's angle of attack can be downward as with an iron, level or upward. Combined with the natural loft of the club, most golfers are best served hitting the ball on the upswing. Depending on how much clubhead speed you generate, your launch angle will be optimized at a different overall loft. At 105 mph of clubhead speed, for instance, the best launch angle is between 14 and 18 degrees. Considering most golfers hit swing speeds under 100 mph, an even higher launch angle is optimal, so swinging through the ball on the upswing is most beneficial for hitting longer shots.
Square the Clubface
No matter how much club technology is available to you, until you can bring the clubface into the ball square to your target line, you are losing valuable power. Swinging hard doesn't make the ball go far--a square clubface does. When the clubface comes through square, or at 90 degrees to your intended target line, all the weight in the clubhead and all the clubhead speed you've generated are being directed into the back of the ball and the sweet spot of the club. If your clubface is not square and you hit the ball off-center, you are leaking power from either the heel or toe of your club. Since a golf club is so long and the ball is so far from your hands, a good way to think about this is to imagine the back of your left hand (right hand for left-handed players) as equivalent to the face of your club. Whatever the back of your hand does, the face of your club does. Therefore, if the back of your hand is square at impact, so is your clubface.