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 vxvx

Velocity Gradient  The resistance tends to keep the fluid in place. Law of inertiaLaw of inertia  The fluid moves most near the object and least farther away.  This is a velocity gradient. y vxvx F

Law of Viscosity  Newton combined these two proportionalities.  This is the law of viscosity. A is the area of the solid sliding on the fluidA is the area of the solid sliding on the fluid  The constant  is the dynamic viscosity and depends on the type of fluid. y vxvx F

Poiseuille’s Law  Flow in a tube is affected by sides in all directions.  The relationship between velocity and distance is  The total volume flow rate is r vxvx P1P1 P2P2 L

Drag Force  Objects falling through a fluid reach terminal velocity.  For low speeds this is due to viscocity.  Stokes’s Law describes the drag force. FgFg FbFb FdFd

Surface Tension  Liquid molecules attract each other.  At the surface this force is the surface tension. Force per length parallel to the surface.Force per length parallel to the surface. Constant for different liquidsConstant for different liquids next insect leg on water