Mechanical Waves
A wave is a disturbance that transfers energy from one place to another by the vibration of particles.
Mechanical waves are periodic disturbances that move through a medium.
The medium itself goes nowhere, but the particles which make up the medium vibrate and transfer energy to their neighboring particles. The energy is therefore passed along the medium without the particles themselves changing position. Mechanical waves can travel through various mediums; gases like air, liquids like water, solids like wood. Electromagnetic Waves, such as light, do not need a medium to pass through. We will study these later. |
There are two types of mechanical waves; transverse and longitudinal which can be represented as diagrams.
Transverse Wave:
As a transverse wave moves, the particles
in the medium move across, or at right angle to, the direction of the wave.
Transverse waves consist of high parts or peaks called crests and low parts called troughs. The distance between two successive crests or two successive troughs is the wavelength for a transverse wave. The height of the crest from the undisturbed position or the depth of the trough from the undisturbed position is the amplitude of the wave. |
Longitudinal Wave: Longitudinal waves move the medium parallel to the direction in which the wave moves
Longitudinal waves made up of regions where molecules are close together known as compressions and of regions where the air molecules are farther apart called rarefactions.
The wavelength of a longitudinal wave is the distance between successive compressions or rarefactions. The amplitude is the maximum distance the vibrating particle travels from its undisturbed distance. |
There are four key properties of waves; amplitude, wavelength, frequency and speed.
Amplitude: The maximum distance the particles of a medium move away from their rest positions as a wave passes through a medium.
Wavelength: The distance between two corresponding parts of a wave (crest and crest or trough and trough)
Frequency: The number of complete waves that pass a given point in a certain amount of time. Frequency is measured in Hertz (Hz). If a wave occurs every second it has a frequency of 1 Hz.
Speed: The speed of sound waves is a product of wavelength and frequency: Speed = wavelength X frequency.
Speed = wavelength x frequency
Frequency = speed / wavelength
Wavelength = speed / frequency.
If a medium does not change, the speed of a wave is constant, so what will happen if we increase the frequency of a wave?... The wavelength must decrease.
Wavelength: The distance between two corresponding parts of a wave (crest and crest or trough and trough)
Frequency: The number of complete waves that pass a given point in a certain amount of time. Frequency is measured in Hertz (Hz). If a wave occurs every second it has a frequency of 1 Hz.
Speed: The speed of sound waves is a product of wavelength and frequency: Speed = wavelength X frequency.
Speed = wavelength x frequency
Frequency = speed / wavelength
Wavelength = speed / frequency.
If a medium does not change, the speed of a wave is constant, so what will happen if we increase the frequency of a wave?... The wavelength must decrease.