First off, a backspin imparted on a golf ball will cause the ball to gain loft and stay in the air longer. As the ball spins in the air, it directs more airflow up over the top of it and then downward behind it. This means that the air above the ball is moving faster than the air below the ball, and because of the pressure difference, the ball has additional force pushing it up, which helps it stay in the air for a longer period of time. This spin also helps golfers produce more accurate shots because with a backspin imparted on the ball, it drops quicker toward the end of the shot. And after hitting the ground, the backspin helps slow the ball more quickly. So the path the ball takes in the air is not a simple parabola. It is a parabola that rises more gradually at first and then comes back down more quickly after reaching its peak. Here are some examples of the paths a ball would take with different amounts of backspin:|
Dimpled golf balls fly much further than smooth balls. Before discussing why this is true, we need to understand something called the boundary layer. The boundary layer is the thin layer of air surrounding a ball as it flies. In the boundary layer, the speed of the air varies from the air on the surface of the ball (which is not moving relative to the ball) to the air out by the mainstream airflow, at the edge of the boundary layer. The reason dimpled balls travel further than smooth balls is because the dimples on a golf ball create turbulence in the boundary layer. This actually helps because the dimples then scoop air back towards the rear of the ball. By moving more air to the rear, this helps keep the air pressure behind the ball from dropping. And by doing this, the amount of air pressure pulling backwards on the ball is decreased. Here is a diagram of the affect of dimples with varying depths on a golf ballís distance:
The wind effects on a ball seem rather obvious. As discussed earlier, the golfer will have to adjust for any type of wind that is present while taking a shot. If there is a tailwind, hitting the ball high will maximize distance by letting the wind do more work in pushing the ball along. However, if there is a head wind, you should hit the ball lower than normal as headwinds destabilize the ball and tend to emphasize a slice or hook. Cross-winds will make the ball drift to the side, in the direction the wind is blowing, so you will need to aim into the wind to compensate. Windís effects on golf are very easy to understand, it is simple vector addition. A cross wind blowing perpendicular to the ballís intended path would be much like the physics problem we did in class involving a person trying to row a boat across a river with a current pushing them sideways.