Reflected Sound Waves when a sound wave encounters an object, some energy is absorbed by the object but most is reflected or diffused around the object. The wave amplitude of the Rayleigh wave diminishes exponentially with depth. Note 2 : the propagation velocity of a Rayleigh wave is slightly less than that of a shear wave in the solid. Note 1 : a maximum particle displacement away from this initially undisturbed surface the motion of the particle is opposite to that of the wave. Rayleigh Wave Definition (IEC 801-23-12) surface wave associated with the free boundary of a solid or liquid such that a surface particle describes an ellipse whose major axis is normal to the surface, and whose centre is situated on the initially undisturbed surface Sound Waves related terms - listed alphabeticallyĪntinodes, the maximum amplitude of a sound wave, occurring halfway between two equally spaced nodes (zeros), see also standing waves. Sound Wavelengths range from more than 17 metres to less than 17 millimeters, between the peaks ( antinodes), so react differently with 'objects' in their paths, resulting in complex sound fields. In the special case of standing waves these node(s) would be stationary. Observe also the nodes and antinodes, found in all waves as they move along the rope. In both cases the rope particles are involved but without any net particle movement. You can simulate sound waves while holding a length of rope and moving your hand(s) up and down or side-to-side, demonstrating the two main directions in which sound wave motion occurs, longitudinal and transverse. Sound Waves in air are longitudinal waves. Remember the equation: speed = frequency x wavelength, so if the wavelength decreases but speed stays the same, then the frequency must increase.Sound Waves Definition (IEC 801-23-01) disturbance propagated at a definite velocity in a medium in such a manner that at any point in the medium the quantity serving as the measure of disturbance is a function of the time, while at any instant the same quantity at a point is a function of the co-ordinates of the point. The change in wavelengths result in a change in frequency. As the ambulance moves, it approaches the sound waves ahead of it, causing the wavefronts to become closer together (they now have a shorter wavelength) while the wavefronts behind the vehicle become more spread out (they now have a longer wavelength). This happens because the sound waves have a constant wave speed. You will have experienced the Doppler Effect when an ambulance or police car with its siren blaring passes you - the pitch of the siren sounds higher when it comes towards us and lower when it is travelling away from us. It appears as if the frequency of the wave changes as the source moves past you. The Doppler Effect occurs when a wave is emitted from a moving source. In the diagram illustrating the Doppler Effect below, the wavefronts are represented as black circles. The distance between each wavefront is equal to one wavelength. The next wavefront would be drawn at the next peak. A ‘ wavefront’ is an imaginary line that is drawn across the peaks of the different waves. When a source emits a wave, it’s not just an individual wave which is emitted but several that are travelling in the same direction. You’ll learn more about EM waves on the next page. All EM waves travel the same speed through a vacuum but they have different wavelengths and frequencies. There are seven different types of EM waves which form are organised along a spectrum - we call this the electromagnetic spectrum. Unlike sound waves, they do not require particles to carry the vibrations which means they are able to travel through a vacuum. Electromagnetic wavesĮlectromagnetic (EM) waves are transverse waves, which means the vibrations move up and down (at right angles) to the direction of wave travel. Sound waves require particles to carry the vibrations, which means they cannot travel through a vacuum (as there are no particles). The speed of sound depends on the medium through which it is travelling, for example, sound waves travel over four times faster in water compared to air. the vibrations are parallel to the direction of wave travel). Sound waves are longitudinal waves, which means they travel through vibrations moving back and forth (i.e.
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