الموضوع: ليه أحسن سرعة 90 كلم/س؟

المشاركة الأصلية كتبت بواسطة MMamdouh

i write much faster in english myself so it is not a problem for me at all

i have no idea about the dents on golf balls... i only know that air pressure rifle pellets are slimmer from the middle for directional stability



and the same thing applies to the fact that the pellet is revolving around its axle while it is shot

seems like aerodynamics is far more deep than we thought

MMamdouh

Let me just put those two theories:

First, any thing that rotates around itself creates negative pressure on one side and positive pressure on the opposite side and this generates a force sometimes we call it Lift.
Example:
In football, when you shoot the ball with a spin the ball makes a curve due to this force.

Second, when you move a body in the air or any other fluid and this body has different length on one side than the other side you get also this lift force. This is actually the theory of flying.
Example:
We talked about the lift under the car because the top of the car is longer than the bottom.

For the golf ball, the ball is required to go far and in order to do that you have to give it an initial high velocity (strong hit). Due to this high speed a negative pressure is generated behind the ball because of the vacuum and this means a high drag force.
So although you hit very strongly you create an opposite force.
The reason of the negative pressure is that the air flow separates from the surface of the ball due to high friction. So the trick is to prevent the air flow from separating and this can be done by creating turbulence in the air flow by introducing the dents on the surface of the ball. This is to reduce the difference between the negative and the positive pressure thus reducing the Drag force