The Dynamics of the Ball

I need to thank Steve Haake, who did his PhD on golf ball impacts for his help on this article. This is a genera look at what happens from tee to green with the ball.  

So… you’re on the tee with the ball teed up for play.  You have selected a driver and begin to swing.  The club head is taken back and comes down to meet the ball on the tee, in theory (but rarely in practice) like Tiger.  It would take an expert in biomechanics, which I’m not, to explain how the complex action of the muscles actually get the club to the ball.  The shot needs about 2 ½ kilowatts of power from you.  This is equal to about a tenth of the power of a small car.

Next, assuming you play somewhat better than I do, (which is not too hard to accomplish) some of the energy built up in the swing is given to the ball during the time of contact between the club and the ball.  This only takes 0.000450 of a second, or much quicker that you can blink.  The ball shoots off into the air at 160 mph, about three times faster that the speed limit on I494, and about twice as fast as most drive on I494.  By the time your hands feel the shot, the ball is ¾ of an inch away from the face.  By the time your brain receives the information and tells your hands what to do to correct the shot, the ball is 15 feet away and moving out fast.  In that, short time of contact with the club, the ball has picked up backspin of about 3,000 rpm’s. 

The ball is now air born and flying off into the distance seeming to hang in the air then suddenly drops toward the end of the flight.  To understand this movement you need some basic aerodynamics.  Think of your golf ball moving in a straight line through the air (If we were thinking about my golf ball, it wouldn’t be a straight line).  There are little swirls created behind the ball like the wake of a boat.  The bigger the wake the more drag and the slower the ball flies.  A smooth ball has a large wake, while a ruff or dimpled ball has a smaller wake.  Dimpled golf balls travel further.

Remember us mentioning that the ball has backspin.  The spin causes the wake of air behind the ball to be deflected down towards the fairway.  This has an equal and opposite reaction giving the ball lift.  It is this lift that causes the ball to hang in the air for so long (about 5 seconds).  Eventually the drag slows the ball down and it falls to the green…the rough, a trap, whatever.

To understand what happens as the ball lands on the green requires knowledge of dynamics, tribology, and biomechanics.  With Steve’s help we’ll make it simple.  The bounce of the ball depends upon where it lands and what the green is like.  Let’s assume the green is flat and has the same hardness all over it.  The ball hits the green and immediately starts into a skid across the turf.  The grass layer comes up in a long pitchmark, much like slipping on a rug on a slick wooden floor.  The ball rebounds at about the same angle that it came in, but slower, and still with a small amount of backspin.  On the next bounce the backspin stops the ball almost dead in its tracks, and sometimes it even screws it back across the green.  The backspin is where the skill of the golfer comes in.  If you don’t get a lot of backspin, the ball doesn’t stop.  Top professionals get up to 10,000 rpm’s of backspin on their shorter shots.

Once the ball has stopped on the green all you have to do is get the ball in the hole.  To use dynamics again, when you take your putt, the putter makes the ball bounce slightly in the air with a small amount of backspin.   The first part of the motion of the ball across the green consists of shallow bounces and skids.  The ball then starts to roll along the turf where it hopefully falls in the hole.

So there you go, from tee to hole.  A simple, but yet semi-scientific look at the dynamics of the ball.   We’ll take some closer looks in the next few issues.