The spring constant and its unit
What happens when forces deform elastic bodies? The simplest example is a spiral spring, the deformation of which can be described with the spring constant (including the physical unit).
How much does a spring deform?
Branches of trees are bent by the force of the wind, tennis rackets are dented by the blow on the ball. Many objects return to their original shape after being deformed by an external force - they are elastic. The simplest model for such deformations are coil springs:
- A typical school experiment in connection with the stretching of such springs is attaching different weights and measuring the respective extension.
- If one plots the acting force (it is the gravitational force or the force of gravity) against the extension graphically, this results in elastic springs a linear relationship: the force F (in the unit N for newtons) is proportional to the extension s (in the unit m for meters or cm for centimeters). In other words: If you double the attached weight, for example, the extension of the spring is also doubled.
Incidentally, the following applies to the force F, if it acts as a gravitational force: F = m * g, where m is the mass of the attached body in kilograms and g is the acceleration due to gravity (g = 9.81 m / s²).
Spring constant - definition and unit
- However, when you experiment with different springs, you will find that they change when a weight is attached behave differently: Some feathers can be stretched easily (i.e. with little effort), while others only have large weights little effect.
- This is where a material property of these springs comes into play, which is called the spring constant. This is the relationship between the force F applied and the path extension s. In formula notation you get D = F / s, where D is the spring constant. Mathematically, D is nothing more than the constant of proportionality between force and elongation.
- The definition also gives the unit of the constants, namely Newtons per meter (or Newtons per centimeter), abbreviated to N / m.
- Conversely, if the spring constant D is known, then the relationship between force and elongation can be determined using Hooke's law. The following applies: F = D * s. This law also applies to the compression or twisting of bodies.
The English researcher Robert Hooke dealt with the elastic behavior ...
However: The spring constant D is of course only constant in the elastic range of the spring and Hooke's law only applies there. If you overstretch springs, you get into the plastic area. Even rubber bands or balloons do not strictly follow this law.
