1/5/2024 0 Comments Resistance physics calculatorIn the hydraulic analogy, current flowing through a wire (or resistor) is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Pushing electric current through a large resistance is like pushing water through a pipe clogged with hair: It requires a larger push ( electromotive force) to drive the same flow ( electric current). When a pipe (left) is filled with hair (right), it takes a larger pressure to achieve the same flow of water. The hydraulic analogy compares electric current flowing through circuits to water flowing through pipes. ![]() The resistance R of an object is defined as the ratio of voltage V across it to current I through it, while the conductance G is the reciprocal: All objects resist electrical current, except for superconductors, which have a resistance of zero. For example, a wire's resistance is higher if it is long and thin, and lower if it is short and thick. The nature of a material is not the only factor in resistance and conductance, however it also depends on the size and shape of an object because these properties are extensive rather than intensive. This relationship is quantified by resistivity or conductivity. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. The resistance of an object depends in large part on the material it is made of. The SI unit of electrical resistance is the ohm ( Ω), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ℧). Electrical resistance shares some conceptual parallels with mechanical friction. Its reciprocal quantity is electrical conductance, measuring the ease with which an electric current passes. The electrical resistance of an object is a measure of its opposition to the flow of electric current. This leads to a decrease of the tire flexing energy and due to the smaller contact patch, to a decline of the frictional component of resistance. ![]() This happens because an increased internal pressure leads to a further stiffening of the tire, which means that the tire deflection decreases at steady state load. As the air pressure increases, the rolling resistance coefficient decreases. In the image below you can see the influence of tire pressure on the rolling resistance coefficient. In reality, the rolling resistance coefficient depends on several factors, like: Table: Rolling resistance coefficient of a vehicle at low speed on a given road Rolled, firm gravel wear down, washboard asphaltĪdditional values for the rolling resistance coefficient can be found in for different pavement types at low vehicle speeds. ![]() New, firm asphalt concrete small pavement cobblestone pavement Table: Coefficients of rolling resistanceįrom we can also extract a table of rolling resistance coefficients function of road surface. For example in, you can find the value of the rolling resistance coefficient function of the road type. There are several sources of automotive literature, in which you can find the value of the rolling resistance coefficient, function on several parameters. The rolling resistance coefficient slightly increases with the increase of the traveling speed of the vehicle. According to, under normal operating conditions, with the vehicle speed below 200 kph, the rolling resistance coefficient is between 0.01 – 0.02. In general, for low vehicle speeds, the value of rolling resistance coefficient is constant. ![]() The rolling resistance coefficient of a tire depends on tire construction, materials, air pressure, vehicle speed, and road conditions.
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