Resistance

In physics, resistance is the measure of the opposition to the flow of any physical quantity, not just electric current.  For example, the resistance of a fluid flow is measured by the pressure drop that is required to produce a given flow rate.  The resistance of a solid material to deformation is measured by the force required to produce a given strain or displacement.

In general, resistance is related to the properties of the material and the conditions of the system in which the flow or motion is taking place.  For example, the resistance of a fluid flow is affected by the viscosity of the fluid, the size and shape of the flow channel, the velocity of the flow, and the pressure difference driving the flow.  Similarly, the resistance of a solid material to deformation is affected by the strength, stiffness, and plasticity of the material, as well as the size and shape of the object being deformed and the conditions of the loading.

In all cases, resistance represents a loss of energy or efficiency in the system, and is an important consideration in the design and analysis of physical systems.