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Bernoulli's principle

Spherical object in a fluid flow

Stream lines of a source (hair dryer) and resulting force for a fluid flow around a sphere. The flow streams from the left to the right in the picture starting from the source. Places where the density of stream lines is large correspond to high average speed of the fluid molecules and vice versa.

When we go around the surface of the sphere, then we find places where the density of streamlines is larger and other places where that density is smaller. This may give us an idea of how the pressure on the surface varies from place to place. Places where the density of streamlines is large indicate that the speed is high there and consequently, according to Bernoulli's principle, the pressure low. On the other hand, at places where the density of streamlines is lower, the pressure is higher.
When we add all forces on the surface of the sphere, then we obtain a resultant force as indicate by F in the streamline picture. Contrary to the previous example, here the force F acts through the center of the sphere and points towards the source. For a light sphere, like a ping-pong ball, that force moves the ball towards the source of the airstream.