There are few things as thrilling as hitting a perfectly straight drive and watching the ball split the fairway some 250 yards away.
Okay. Maybe "thrilling" isn't the best word but there is a certain majesty to watching a well hit drive.
It is an exercise in intuitive science as many things are. We don't need to understand the complex mathematical equations that define the ballistic trajectory of the ball or the physics at play at the moment of contact or the chemistry of the composite used in putting the ball together. These are "givens" - stuff that we learn by doing without the benefit of a classroom or a science education.
Still, understanding a bit of the science can certainly help to explain the results and maybe even improve one's game.
For me, a perfectly straight drive is a rarity. More often than not, when I hit a golf ball it bends one way or the other - either a hook or a slice. Sometimes these can be quite dramatic sending the ball in truly strange directions!
Scientifically speaking, the amount a ball deviates from a straight line once it has been hit is a result of the interaction of the surface of the ball and its spin. Indeed, like a soccer ball, baseball, frisbee, or any other object, the spin of a golf ball alters its flight path.
This is a consequence of something called the "Magnus Effect" which derives from a more fundamental principle discovered by Bernoulli in 1738. Bernoulli found that the pressure that a fluid or gas exerts is related to how fast it is moving. The faster a gas or fluid flows, the lower the pressure.
Bernoulli's Principle accounts for some of the "lift" experienced by airplane wings. The shape of an airplane wings is such that they are longer on the upper surface than the lower. This means that air travelling above a wing has a longer path and must travel faster to reach the same point at the trailing edge.
The result is that the upper surface experiences less pressure. The pressure differential between the upper and lower surfaces results in an unbalanced force and the wing is literally pushed upwards by the air below it.
With a golf ball, the pressure differential is not so much top and bottom as side to side, as golf balls can leave the club face with a lateral spin. Still, this spin means that the air on each side of a ball will have different velocities.
If you were to look at a ball from above, with a clockwise spin, then the right hand side of the ball will have the ball and the air moving in the same direction resulting in an increased velocity. On the left hand side, the ball is moving against the wind resulting in a decreased velocity.
The different velocities mean differential pressure and the ball curves in flight, in this case, towards the right. It slices as a result of this "Magnus Effect".
Controlling the lateral spin of a ball is important if one wants to get a long, straight drive. For some golfers, they can even control the spin to the point that they can deliberately draw or fade a shot into the green or around an obstruction. Alas, that is not part of my game.
The truly great golfers can impart backspin which increases distance but once the ball has left the club face, "drag" or the resistance of air to the movement of the ball takes over.
Below a critical speed, the flow of air over a spherical surface is slow enough that the molecules of air can get together smoothly on the other side. The sphere passes with little disturbance in streamlined flow.
Above a critical speed, the air molecules do not flow smoothly resulting in turbulence. Little whirlpools and eddies form which use up energy and slow the golf ball down.
The amount of drag is directly related to how fast an object is moving and puts an upper limit on achievable speeds. For example, drag is partly responsible for the terminal velocity of a skydiver.
Drag can be diminished by dimpling the surface of a golf ball. This disrupts the layer right next to the ball in a way that lowers the drag coefficient. Without dimples, even Tiger Woods or Rory McIlroy would have trouble hitting a ball more than 200 yards.
The dimples also help with distance as a well hit ball will only have backspin and no lateral spin. The result is that the air pressure will be lower on top, helping to keep the ball in the air for longer and making it travel straighter. The dimples help to maximize this lift or "Magnus Effect".
If done well a thing of beauty, a long straight drive, results.
