And this ultimately controls the volume of blood that actually reaches our tissue or organ of our body. Now, let's discuss something known as the volume flow rate. So the volume flow rate is simply the volume of blood that passes our blood vessel over some given period of time. And in physics and from fluid dynamics, we know that our volume flow rate of the blood queue is equal to the change in pressure between some .1 and some .2 inside our blood vessel divided by the resistance of that blood vessel. Now, if we take this equation and we plug it in for the resistance, we basically get the following equation. So Q is equal to pi radius, the power of four multiplied by the change in pressure divided by a multiplied by the viscosity multiplied by the length of that blood vessel.