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Flight Dynamics of Golf Balls
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It is the combination of the lift and drag properties of the ball, as well as its speed, launch angle and spin rate,
which will dictate the flight path or trajectory of the ball, and thus the distance it will go.
Since the early human notion of air and speed as a
lifting force, technical textbooks have explained rotating
balls in terms of the Bernoulli effect - the spinning ball
drags a sheath of air around with it; due to superposition,
there is higher gas velocity where the spin adds to the
velocity of the streaming air creating a lower pressure at
that point and the ball moves in the direction of the leading
edge.
This is not so much incorrect as incomplete. The rest
of the story is the Magnus effect, a peculiar lifting force
experienced by revolving bodies traveling through a fluid
medium.
Magnus lift is present because a driven golf ball has backspin that warps the airflow much like the angled wing
and a regular, dimpled texture that creates drag. The Magnus force can be thought of as an upward push due to the
relative dimpled drag on the air at the top and bottom portions of the golf ball: the top portion is moving slower relative
to the air around it, so there is less drag on the air that goes over the ball.
A thin layer of air next to the ball, called the boundary layer, becomes turbulent. Rather than flowing in a
continuous, laminar boundary layer, it has a microscopic pattern of fluctuations and randomized flow. In short, a
turbulent boundary layer has better tires; meaning that the air grabs portions of the golf ball and slows down the rotation
almost like a well-treaded tire gripping against a road.
A smooth golf ball
A golf ball with wire hoop around it, simulating a rough surface
represented by dimples
Air travels around the ball further before separating, creating a smaller wake and much less drag while the
spinning motion warps the airflow to generate lift as shown in the flow pattern.
Surprisingly, the phenomenon described above gives a dimpled golf ball only about half the drag of a smooth
one. A perfectly smooth golf ball with no dimples would travel about 130 yards when hit with a driver by a good player.
On the other hand, a ball with well-designed dimples, struck the same way, will travel about 290 yards.
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