This article is about vibration. We will explain to you what a vibration is, what conditions must be met for it, what parameters it describes and which types you have to distinguish with regard to them. This article is assigned to the school subject physics and shows you everything you need to know about vibrations. As you will see from the following examples, we encounter them in many areas.
What are vibrations?
One vibration (oscillation) is generally one periodic change over time one or more physical quantities in a physical system.
We will look at mechanical vibrations as an important special form. These only describe processes in which a body regularly moves around an equilibrium position (rest position). In such cases, the inertia of a body to maintain this movement causes the body to move past the equilibrium position. This is the reason why an oscillation around the position of equilibrium is also recorded. In the following, we shall now be concerned precisely with such mechanical oscillations.
Prerequisites for the occurrence of mechanical vibrations
In order for a mechanical vibration to occur at all, the following conditions must be met:
- Bodies or particles capable of vibrating must be present.
- Bodies or particles capable of vibrating must be deflected from their equilibrium position (rest position).
- Repelling effects must be present that cause the body or the particles to move back towards the equilibrium position after the deflection.
Examples of mechanical vibrations
As an everyday example of mechanical vibration, think of a swing. If it is pushed once, it swings back and forth like a clock pendulum or like a thread pendulum. The body capable of vibrating is the seat with a person sitting on it. An oscillation occurs when the swing is deflected from its equilibrium position. You can cause this by pushing from the outside or by your own body movements.
Fig. 1: Rocking as a mechanical vibration
from: https://www.grund-wissen.de/physik/mechanik/schwingungen-und-wellen/schwingungen.html
In this case, the restoring force is the force of gravity. It causes the body to move from point A towards the resting position (point B). It works until the body has reached the resting position. Due to its inertia, the body moves beyond the resting position to point C. The weight force first causes the movement to slow down to zero speed (point C) and then moves back towards the resting position.
The potential energy also changes. It is maximum at points A and C and zero at point B. In contrast, the kinetic energy is zero at points A and C and maximum at point B.
Fig. 2: Physical representation
from: https://www.lernhelfer.de/schuelerlexikon/physik/artikel/mechanische-schwingungen
Parameters for describing mechanical vibrations
You can describe a vibration with the following parameters:
- The elongation (deflection) is the respective distance of the vibrating body from the equilibrium or resting position. The deflection is thus a time-dependent variable.
- The amplitude (oscillation width) is the maximum deflection at the reversal point, more precisely its amount. It is a constant for every oscillation process.
- The period T (period of oscillation) is the time required for a full oscillation.
- The frequency f is the number of oscillations per second. It holds that f = 1/T. It is also given in units of Hertz (Hz). A frequency of 1 Hz = 1/s means that exactly one oscillation process takes place in one second.
You can show the course of a vibrating body over time using a displacement-time diagram. This results in a periodic curve that is characteristic of the respective oscillator.
Fig. 3: Spring pendulum
from: https://www.grund-wissen.de/physik/mechanik/schwingungen-und-wellen/schwingungen.html
Types of mechanical vibrations
Mechanical vibrations can generally be differentiated according to the type of energy input and the form of the vibrations.
Depending on the type of energy supply, a distinction is made between
Depending on the shape of the oscillations, a distinction is made between
Free and forced vibrations
If an oscillating system is stimulated and then left to its own devices, it will oscillate at its natural frequency. Such free vibrations performs, for example, a tuning fork that is struck once and then continues to vibrate. This also applies to strings of musical instruments, which are also struck once.
However, if the energy is supplied periodically over a longer period of time, the oscillating system leads forced oscillations with the frequency of the exciting system. For example, a machine can excite the foundation on which it stands to forced vibrations.
Harmonic and aharmonic vibrations
If the path-time function of an oscillation is in the form of a sine function, it is called harmonic, otherwise it is called aharmonic.
Fig. 4: Harmonic and aharmonic oscillation
from: https://www.lernhelfer.de/schuelerlexikon/physik/artikel/arten-mechanischer-schwingungen
Undamped and damped vibrations
A body left to its own devices always performs damped oscillations, since friction always occurs and part of the mechanical energy is converted into thermal energy and given off to the environment as heat.
If a body is to oscillate undamped, the energy that has been converted into thermal energy by friction must be periodically returned to it. This happens, for example, with a clock pendulum using a weight.
In the case of damped oscillations, it should be noted that although the amplitude decreases over time, the oscillation time and thus the frequency remain the same.
Fig. 5: Undamped and damped oscillation
from: https://www.lernhelfer.de/schuelerlexikon/physik/artikel/arten-mechanischer-schwingungen#
The vibrations – everything important at a glance
- One vibration (oscillation) is a periodic change over time one or more physical quantities in a physical system.
- The mechanical vibration as a special form represents a regular exercise of a body by one equilibrium position (resting position).
- As a prerequisite for the emergence of mechanical vibrations must vibratory bodies or particles be present, which are deflected from their equilibrium position and also by restoring forces be moved back towards the equilibrium position.
- Everyday examples of such vibrations are moving ones Swings, clock pendulums, spring pendulums, tuning forks and musical instruments.
- The parameters are used for description elongation, amplitude, period and frequency used.
- Mechanical vibrations can be differentiated according to the type of energy input (free and forced vibrations) and their form (harmonic and aharmonic as well as undamped and damped vibrations).
FINISHED! On the one hand you now know what vibrations are and on the other hand you are now able to classify and describe them in meaningful physical contexts. You can find articles on this and many other topics, exercises and helpful literature on .