Understanding Wave Motion: Types and Properties
Waves move up and down any object, but not in the direction in which the waves are advancing. When at rest, the object is in its initial position. Wave motion is a form of power transmission, with no net transport of material, through the propagation of any form of disturbance. This disturbance is called a wave. In any wave propagation phenomena, we can see some common elements:
- An initial perturbation that is transmitted to other points, with no net movement of matter.
- A transmission of energy through a medium.
- A delay between the instant the initial disturbance occurs and the moment this reaches successively more distant points.
There are two main types of waves:
- Mechanical waves: Propagation of a mechanical type perturbation through some elastic material medium, transmitting the mechanical energy of the wave. Example: sound waves.
- Electromagnetic waves: Electromagnetic energy transmission through the propagation of two oscillatory fields, electricity and magnetism, that require no physical environment and that are periodic variations of the electric and magnetic state of space. Example: X-rays
Types of Mechanical Waves
Mechanical waves can be classified taking into account the direction of propagation of the wave:
- Transverse waves: If we give a sudden jolt upright, a ridge or lump called a pulse wave or pulse is formed. This is a perturbation that is transmitted through a traveling wave. A wave is transverse if its direction of propagation is perpendicular to the direction of oscillation in the particles that cause the disturbed environment.
- Longitudinal waves: If we take a spring, fixed at one end, and apply a sudden horizontal movement of compression and expansion, left and right. A wave is longitudinal if its direction of propagation is parallel to the direction of oscillation in the particles that cause the disturbed environment.
- Surface waves: Produced in a liquid feature, particles swing both parallel and perpendicular to the direction of propagation of the wave. Example: dropping a pebble in the water.
Harmonic Waves
Harmonic waves are caused by periodic disturbances produced in an elastic medium by simple harmonic motion. Harmonic wave features include:
- Wave amplitude (A): The maximum value of elongation of the particles of the medium in their oscillations.
- Wavelength (λ): The minimum distance between two consecutive points that are in the same state of vibration.
- Period (T): The time that wave motion uses to move one wavelength.
- Frequency (f): The number of waves that pass through a point in the environment per unit of time.
Wave Function and Intensity
The wave function (y) represents the value of elongation for each point of the medium as a function of time. The intensity of the waves on a wave front have the same state of vibration, vibrating in phase. Waves can propagate on a surface or in space. The direction of wave propagation is perpendicular to the front, and its speed is the same in all radial directions. The intensity (I) of a wave is the energy per unit time through a unit area perpendicular to the direction of propagation of the wave.
Attenuation and Absorption of Waves
- Attenuation: The propagated energy is distributed over the surface of the wavefront, and the number of particles in vibration increases. Therefore, the energy that reaches each particle is smaller, and they vibrate with less energy. This phenomenon is called attenuation, or the natural diminution of energy.
- Absorption: The friction of the particles of the environment and other causes produce energy absorption, whose magnitude depends on the nature of the medium of propagation of the wave.
Sound Waves
Sound is a vibration or mechanical derangement of any body that is propagated as waves through any elastic material medium. There are two types of sound waves:
- Infrasonic waves: Frequencies lower than 20 Hz. Example: earthquakes.
- Ultrasonic waves: Frequencies above 20,000 Hz. Example: induced vibrations in a quartz crystal with an alternating electric field.