Transcript Viscosity
Viscosity Fluid Resistance An object moving through or on a fluid meets resistance. Force causes the fluid to move. The velocity is proportional to the force. F vx vx F Velocity Gradient The resistance tends to keep the fluid in place. F • Law of inertia vx The fluid moves most near the object and least farther away. This is a velocity gradient. vx y y Law of Viscosity Newton combined these two proportionalities. This is the law of viscosity. F vx • A is the area of the solid sliding on the fluid The constant h is the dynamic viscosity and depends on the type of fluid. vx F hA y y Poiseuille’s Law Flow in a tube is affected by sides in all directions. r The relationship between velocity and distance is vx P 2 2 (R r ) 4hL The total volume flow rate is V R 4 P t 8hL P1 vx L P2 Drag Force Fb Objects falling through a fluid reach terminal velocity. For low speeds this is due to viscocity. Stokes’s Law describes the drag force. Fd Fg Fd 6hrv Surface Tension Liquid molecules attract each other. At the surface this force is the surface tension. • Force per length parallel to the surface. • Constant for different liquids insect leg on water next