# Pressure resistance

The pressure resistance (also form resistance ) is the force on a body in flow, which results from the pressure difference between its front and back: ${\ displaystyle F_ {p}}$${\ displaystyle \ Delta p}$

${\ displaystyle F_ {p} = \ Delta p \ cdot A_ {q}}$

with the cross-sectional area . ${\ displaystyle A_ {q}}$

The differential pressure has its origin in power loss of the friction -prone flow (i. E. With viscosity ). Due to the friction, the flow can no longer follow the body contour in such a way that an undisturbed flow can be observed on the rear side; instead, boundary layer separations occur , which in turn lead to turbulence on the back of the body. With the turbulence, the pressure on the back of the body drops, and the aforementioned pressure difference arises. From an energetic point of view, work has to be done to generate the turbulence on the rear side of the body around the body.

The pressure resistance must not be confused with the shear stress resistance , which is caused directly by the friction of the flow on the surface. Together with the shear stress resistance, the pressure resistance forms the total resistance of a body in flow.

## Individual evidence

1. Peter R. Hakenesch: Script for the Fluid Mechanics Lecture , p. 121 ff , (PDF file; 7.19 MB).
2. Peter von Böckh: Fluid Mechanics. 2nd edition 2004, pp. 238-239.
3. ^ Siekmann, Thamsen: Fluid Dynamics , 2nd edition, 2008, p. 225; ISBN 978-3-540-73726-1 .