Vascular transport is the movement of fluids (including gases) through tubes. The major difference in vascular transport between plants and animals is that animals push, while plants push their vital fluid through their vascular system. The flow rate (q) is defined as the difference in pressure between the entry and exit to the system. It is quantified with the following equation: q = p / r , where p = p2 p1 and r is the resistance in the system. Flow rate can be determined by the pressure at the start of the system, the pressure loss in the system, or the resistance in the system. Also note that pressure is proportional to both q and r. Resistance is calculated by the following equation: r = 8 l / r 4, where l is the length of the tube, is the viscosity coefficient and r is the radius (diameter) of the tube.