As a young and curious kid, I was determined to produce fire by rubbing two sticks together. Try as I might, I could never produce enough sliding friction to even make the wood seem warm.
Friction is the motion energy created by the movement of one rough surface against another rough surface and the conversion of that energy to heat energy. As my younger self rubbed the two sticks together, the action created resistance--which should have translated into heat and eventually fire.
Converting motion energy to heat energy can cause problems. The force of rolling friction resists the motion of the ball bearing and--and as heat increases--degrades the bearing surface.
Friction can provide benefits. Static friction exerts pressure on an object at rest and resists movement. Without static friction, our cars would slide over a road surface rather than nicely slowing to a stop when we apply the brakes.
Fluid Friction is the Same But Different
| A fluid rubbing against another fluid or contacting a solid object resists motion. This definition illustrates that fluid friction and solid friction have common characteristics. Yet, the differences between fluid and solid friction become apparent when combining the coefficient of friction with fluid dynamics. The coefficient of friction describes the ratio of the force of friction between two objects and the force that presses the objects together. |
Several factors affect the coefficient of friction value. Because the static force required to place an object in motion is greater than the kinetic force needed to keep an object moving, the values for the coefficient vary. The roughness and dryness of an object also impacts the coefficient of friction. Smooth surfaces have a lower coefficient of friction value with the roughness of a material directly proportional to the coefficient of friction. Dry materials typically have high coefficient of friction values.
The differences between solid friction and fluid friction begin with the properties of fluids--and more specifically--liquids. Every liquid has viscosity--or the resistance to flow. In turn, flow behavior depends on the molecular weight of the liquid and the distribution of the molecular weight. The measurement of viscosity defines the internal friction of a moving liquid.
Several variations become apparent. Friction pushes back against the bottom of a ship while water resistance impedes the movement of the ship through water. The same type of resistance occurs as an aircraft flies through air. Resistance builds around the shape of the aircraft and as the air contacts the aircraft surface.
Along with fluid friction existing through the action of fluids against solid objects, it also appears withing fluid-fluid motion. Water moving over grease or oil causes fluid friction. The weight of one fluid against another generates force between the two fluids and holds back the motion. Friction can also occur between the layers in a fluid.
Energy Costs Increase with Friction Loss
| Reducing friction in a pipe or pumping system designs depends on accurately measuring viscosity.The viscosity of a liquid causes resistance to occur when a fluid moves over the surface of a pipe. Fluid friction exerts force in the opposite direction of liquid flow. This loss of pressure translates into a loss of fluid energy and impacts the design of pumps and piping systems. In a pumping system, fluid friction causes pressure or head loss. |
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The Darcy Equation defines friction head loss through several major loss factors. Those factors include pipe length, pipe diameter, the velocity of the liquid, and the acceleration caused by gravity determine the amount of head loss.
Within the equation, the Darcy friction factor describes the frictional losses in a pipe. The number associated with the Darcy friction factor depends on the turbulent flow and degree of roughness of the inner surface of the pipe. In contrast to the friction factor for turbulent flow, the friction factor for a laminar flow does not depend on the pipe inner surface roughness.
When designing a pipe system, the changes in velocity caused by bends in the pipe or valves, the density of the fluid, and the friction coefficient are minor loss factors. The friction coefficient depends on the type of flow and the roughness of the pipe. Each type of flow refers to a specific formula.
Friction loss causes energy loss. In a pumping system, the height of the liquid—or head—produces pressure at the bottom of the pump. Applying more force increases the pressure but also requires more energy. Any loss of pressure causes a pumping system to work harder as it attempts to maintain the liquid level in a pump or tank. The ability of the pump to produce pressure depends on the flow rate. Because of the need to maintain flow rate and pressure, piping systems that have long lengths of pipe, worn pipes, worn fittings, or damaged equipment also have larger energy losses.
Learn more about the impacts of friction loss for better flow and pressure, energy savings, and enhanced pump performance. It's a simple solution made by physics for easy, alternative methodologies to addressing water quality issues and advancing sustainable practices.
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