# Understanding Spring Constant Dimensional Formula

In the physics of spring design, the spring constant dimensional formula provides the appropriate equation necessary to meet the application requirements of a particular type of spring—such as a compression or extension spring. A dimensional formula relates fundamental units like meters and kilograms into dimensional quantities such as mass and length to express an equation and, for spring design, the spring constant dimensional formula anticipates how a spring will behave in an application. The spring constant, articulated in Hooke’s Law, is the restoring force that is exerted by a spring to return it to its original position after it has been displaced by an external force. In other words, the force applied to a spring is directly proportional to its displacement, whether compressed or extended. The constant of proportionality as defined in Hooke’s Law is the essence of the spring constant.

For design considerations then, the importance of calculating the spring constant is to determine how much force is required to deform a spring and return to its original position. The calculation is needed to measure a spring’s stiffness and the required load to stretch or compress it. The higher the spring constant is, the stiffer the spring. Stiff springs carry greater loads because they are more difficult to displace, i.e., stretch or compress. Lower spring constants would allow for greater displacement.

The Importance of the Spring Constant Dimensional Formula for Manufacturers

Calculating the spring constant dimensional formula matters for spring design in order for manufacturers to know how the spring will behave in an application. Though it is obvious that same spring used for a shock absorber in an automobile’s suspension system would not work in a Pogo stick, for many mechanical applications there are minute differences in spring behavior that will determine whether the application can function or not.

This is particularly true for springs used in, say, medical applications. An incorrect dimensional formula for the spring constant of a spring used in an application to enlarge blood vessels could result in the wire being too thin or the displacement too high, which could cause a life-threatening rupture. On a much larger scale, the spring design for a tractor trailer’s suspension system must be precisely calculated to provide the necessary shock absorption without destabilizing the truck at high speeds.

As the formula provides the appropriate equation to know the design characteristics of a spring, it also helps to determine the material properties to use in the manufacture of the spring. When a spring is manufactured, there is no guesswork. The spring coiling machines are programmed to produce a spring with the exact measurements as calculated to that they coil the right spring for the application.

The Spring Constant Dimensional Formula

As Hooke’s formula relates to the constant of proportionality, i.e., how much energy is released proportionally, the spring constant is a property of the spring itself. The constant is represented by the algebraic value, k. Mathematically, the spring constant equals the dimension of force, F, over the dimension of displacement, x, and is expressed as F = kx or k = -F/ x. The value of k depends not only on the kind of elastic material under consideration but also on its dimensions and shape, the wire diameter comprising the spring, the diameter of each coil, the free length of the spring at rest, and the number of active coils.

The dimensional formula of the spring constant is derived from mass, length, and time, which is expressed as M, L, and T, in relation to force applied, F, times the displacement, x to equal, k, the spring constant. In calculating the dimensional formula of the spring constant, where the dimension of F = [MLT-2] and the dimension of x = [L], therefore, the dimension of k = [MLT-2]/[L] = [MT-2], and is expressed as [M1L0T-2 ].

The importance of calculating the spring constant in any application is critical to ensure the right spring will be coiled, as intended, for the application. For manufacturers, determining how much force will be required to deform a spring cannot be left to guesswork or approximation. If you have questions about calculating the spring constant dimensional formula to meet your application needs, contact James Spring for a custom solution!