Wave . Wave motion, upon transmission of a disturbance. What happens when a wave is produced is that energy is transported from one place to another without the transport of matter. When an earthquake strikes , for example, the energy carried by the waves is so enormous that it can cause buildings to collapse or large cracks to open in the ground , without there being a lateral displacement of earth from one place to another.
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- 1 Origins
- 2 types
- 3 Speed
- 4 Length and frequency
- 5 Wave properties
- 6 characteristic sound waves
- 7 Sources
When they throw a stone into a raft or pond in which a cork stopper floats , small circular waves form around the point where the stone hits the surface of the water , and the cork moves up and down (oscillates ), but without shifting laterally from its original position, before throwing the stone. Upon impacting the stone against the surface, a disturbance is produced that is transmitted through the water without lateral displacement, neither of the water nor of the cork. A wave motion takes place vertically, forming the successive crests and valleys of the waves.
It is possible to distinguish between two types of waves, mechanical and electromagnetic . Mechanical waves are those that need a material means by which to propagate. For example, an alarm clock emits sound waves that are transmitted through the air, but if we put it inside a glass bell from which all the air inside it is extracted (that is called making a vacuum), we would see that it would still vibrate, but we wouldn’t hear it. In this case, the material medium is air. In the case of the pond, the material medium through which the waves are transmitted is water. And in an earthquake, the material medium is Earth itself .
When we tie one end of a rope to the wall and shake the other end upward, a wave is produced and transmitted by the rope, which is the medium in this case. Electromagnetic waves are waves that do not need the presence of a material medium to propagate. For example, the light that reaches us from the Sun travels to Earth through outer space, where there is no material medium, it is empty space. Radio or television waves, for example, are electromagnetic waves that travel through the atmosphere, but without requiring the presence of air for transmission.
The speed at which a wave propagates is the result of dividing the distance that the disturbance transmitted by the wave travels by the time that has elapsed. The speed depends on the material medium in which the wave propagates. For example, sound (like thunder) spreads through the air at 340 meters per second, while from salt water it spreads at 1,500 meters per second. Light and other electromagnetic waves propagate at the speed of 300,000 kilometers per second.
Length and frequency
Wavelength is the distance between two consecutive crests or valleys of the wave. The frequency of a wave is the number of peaks that pass in one second through a point in the middle where the disturbance is transmitted. Frequency is measured in hertz (unit whose symbol is Hz). A wave of one hertz of frequency passing through a point would form a single crest every second. Since hertz is a very small unit, its multiples are used more, especially megahertz (MHz), which is equivalent to one million hertz. The higher the frequency of a wave, the more energy it carries. Thus, television or radio waves, which have low frequencies, transport less energy than the dreaded ultraviolet rays (you will have heard of the danger posed by the destruction of the ozone layer of ouratmosphere , because it is the one that prevents these rays from the Sun from reaching us).
When a wave collides with an obstacle, these phenomena can take place:
- That part or all of the wave is reflected (reflection). It is what happens when you look in a mirror.
- That part of the wave refracts (refraction), that is, that it continues to travel through the obstacle, but changing its direction of propagation. If you put a pencilin a glass half full of water and we stand to one side, we will see that it seems as if it were broken into two pieces, the one on the outside and the one inside the water.
- If the obstacle is small, it may happen that the wave surrounds it and is not “cut” when it passes. This phenomenon is called diffraction.
Characteristic sound waves
Each musical instrument produces a characteristic vibration. The vibrations propagate through the air forming sound waves that when we reach the ear allow us to identify the instrument even if we do not see it. A tuning fork generates pure sound , and vibrates regularly with a rounded waveform. A violin generates a clear sound and a jagged waveform. The flute generates a smooth sound and a relatively rounded waveform. The fingerboard, violin, and flute play the same note, so the distance between the wave crests is the same on all waveforms. A gongdoes not vibrate regularly like the first three instruments. Its waveform is jagged and random, and the note is generally not recognizable.