How to calculate the static pressure in a pitot tube? In a pitot-static tube, we have two different pressure, the static pressure $p_s$ and the total pressure $p_0 = p_s + \frac{1}{2}\rho v^2$, which comes from the Beroulli equation for incompressible flows. 

Now, lets say we are given an inflow of air from the freestream (assume STP conditions) with a speed of $v_{\infty} = 100$ ft/s. The total pressure would just be $p_0 = p_{\infty} + \frac{1}{2} \rho v_{\infty}^2$, but what I fail to understand is how we would get the static pressure. Would it just be the freestream pressure? Or something else...
The pitot tube is pointed into the airstream and measures the total pressure. Static pressure must be measured, not calculated. It is done so at a separate location, using a static port.



Both pitot tubes and static ports are needed in order to derive air speed, as this incident sadly illustrates.