Wave motion involves the transfer of energy. The behavior of this energy transfer varies with the particular medium of transport and energy form. In general, vibrations propagate in the form of waves. Mechanical waves travel in a material medium, such as a string or a membrane. Acoustic waves travel in fluids, such as air or water.
is initiated by an energetic disturbance that subsequently travels through a medium with a fixed velocity (for homogeneous media). This moving disturbance is referred to as a traveling wave.
A wave propagates through a medium via internal cohesive forces, though the medium itself is not transported.
A simple sinusoidal disturbance of frequency f will produce periodic motion
with a wavelength given by
, where c is the wave speed of propagation. The wavelength represents the distance between successive, periodic movements of a medium.
The wave speed is determined by the mass (or mass density) and elastic modulus (or tension) of the medium in which it travels. A more ``massy'' material will have a lower propagation speed. A ``stiffer'' material will have a higher speed of propagation.
Transverse Wave Motion: vibration of particles in the medium is perpendicular to the direction of wave motion.
are longitudinal disturbances that travel in a solid, liquid, or gas.
The speed of sound in air is approximately given by
c = 331.3 + 0.6 t (meters / second), where t is the temperature of the air in degrees Celsius. A value of 345 meters / second is a good estimate at room temperature.
When a wave encounters a change in the material in which it propagates, wave scattering will occur at that boundary. The way in which waves scatter at a boundary is determined by boundary conditions.
In two or three dimensions, the angle an incident wavefront makes with a large reflecting surface (over several wavelengths in all directions) is equal to the angle of reflection (specular reflections).
A sudden or progressive change in wave speed will produce a change in propagation direction or a ``bending'' of the waves. This is known as refraction.