The Bernoulli Effect     It is found that there is a relationship between pressure and speed  and it was formulated by Bernoulli.  If we look at the stream lines around a ball for an idealized flow, we can see that the stream lines are closer together around the ball than when it was away from the ball.  (See figure 1.)  The air approaching the ball is sped up as it moves around the ball and then it slows down as it goes away from the ball.  With this, it is seen that a change in the speed correlates to a change in pressure.  At lower speeds, the pressure is higher and vice versa.  So, for the golf ball, the pressure is higher in front of the ball.  As the air moves around the ball, it speeds up and thus having a decrease in the pressure.                                                                                                                                 In the previous slide, we have seen that the boundary layer viscosity slows the air down.  We also see that the difference of pressure produces a change of speed in the air flow.  As we follow along the stream line, the air flow speeds up as it moves around the ball, but the air is stopped before reaching the rear of the ball and the flow separates from the ball.  Then viscosity plays a role of slowing the air down and then the flow is then formed into eddies.  The flow beyond this separation is turbulent. Eddies that are formed are confined inside the wake behind the ball. (See figure 2.) These eddies have kinetic energy to which the ball's lost of energy comes from the drag of the air.  As we increase the speed of the ball, the drag force is increased.  It is seen that by doubling the speed, the drag is four times greater.  However, it is seen that there is a critical speed to which there is a drop in the drag force.  This is explained in the next slide.