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## Viscosity

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**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**Velocity Gradient**• The resistance tends to keep the fluid in place. • Law of inertia • The fluid moves most near the object and least farther away. • This is a velocity gradient. F vx y**Law of Viscosity**• Newton combined these two proportionalities. • This is the law of viscosity. • 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. F vx y**Flow in a tube is affected by sides in all directions.**The relationship between velocity and distance is The total volume flow rate is Poiseuille’s Law r P1 vx P2 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. Fd Fb Fg**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