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In physics, Hooke's law is an empirical law which states that the force (F) needed to extend or compress a spring by some distance (x) scales linearly with respect to that distance—that is, F s = kx, where k is a constant factor characteristic of the spring (i.e., its stiffness), and x is small compared to the total possible deformation of the spring.
Compressibility factor values are usually obtained by calculation from equations of state (EOS), such as the virial equation which take compound-specific empirical constants as input. For a gas that is a mixture of two or more pure gases (air or natural gas, for example), the gas composition must be known before compressibility can be calculated.
The following table gives formula for the spring that is equivalent to a system of two springs, in series or in parallel, whose spring constants are and . [1] The compliance c {\displaystyle c} of a spring is the reciprocal 1 / k {\displaystyle 1/k} of its spring constant.)
A torsion spring's rate is in units of torque divided by angle, such as N·m/rad or ft·lbf/degree. The inverse of spring rate is compliance, that is: if a spring has a rate of 10 N/mm, it has a compliance of 0.1 mm/N. The stiffness (or rate) of springs in parallel is additive, as is the compliance of springs in series.
The most common example is in a vehicle's suspension, where it is used to describe the displacement and forces in the springs and shock absorbers. The force in the spring is (roughly) the vertical force at the contact patch divided by the motion ratio, and the spring rate is the wheel rate divided by the motion ratio squared.
The strain rate is measured by the rate of change of the sample radius at its middle. It is calculated using the following equation: ϵ ˙ = − 2 R d R d t {\displaystyle {\dot {\epsilon }}=-{\frac {2}{R}}{dR \over dt}} where R {\displaystyle R} is the mid-radius value and ϵ ˙ {\displaystyle {\dot {\epsilon }}} is the strain rate.
An ideal constant-force spring is a spring for which the force it exerts over its range of motion is a constant, that is, it does not obey Hooke's law.In reality, "constant-force springs" do not provide a truly constant force and are constructed from materials that do obey Hooke's law.
A selection of conical coil springs. Spring rate is the measurement of how much a coil spring can hold until it compresses 1 inch (2.54 cm). The spring rate is normally specified by the manufacture. If a spring has a rate of 100 then the spring would compress 1 inch with 100 pounds (45 kg) of load. [1]