Everything Waves: Sound

  • General Overview of Wave Properties


Power in physics

Centripetal acceleration

Series circuits


Left hand rules

Properties of magnets and motors


Newton's Law of Gravitation

Strong Nuclear Force

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So what are waves all about?

A continuious series of pulses wavesEdit

Well, to begin, a wave is defined as a "continuous series of pulses." A pulse is defined as a "single disturbance." In other words, a pulse is like a bump, and many bumps one after another constitute a wave. Sound waves are mechanic waves, meaning they need a medium (substance) to travel through, such as air. Waves that do not need a medium are electromagnetic (i.e. light).

Longitude or transverse wavesEdit

It is also important to note that sound waves are longitude waves; they travel in the direction they were propelled. More scientifically, the particles of the medium that move to create a wave do so parallel to the wave's travel. The other type of wave other than longitude is transverse. No surprises here- particles travel perpendicular to the direction of wave travel. It's easy to imagine these waves when you think of shaking a rope or spring extending out in front of you back and forth on the floor. When you move your hand from side to side and the wave travels through the rope away from you, the particles of the rope are each moving left to right, perpendicular to the direction the wave actually goes- this is transverse. When you push and pull, let's say a spring, toward you and away from you, the wave travels perpendicular to that motion, which is longitude. There is no source that can emit sound waves by vibrating perpendi to the direction the sound will travel.

All waves share certain properties that characterize them. A dip in the wave up (as in a pulse that is above the line of equilibrium- the x-axis) is called a crest. A low dip in the wave (a pulse below the line of equilibrium) is called a trough. Waves also all have:

  • An Amplitude: "the maximum displacement from equilibrium," or the farthest a wave's crest or trough extends away from the line that is the x-axis in the diagram. This is designated as A, is in meters, and reflects (pun intended!) how much energy the wave is carfrequency is changed, or by the medium if the wave travels through more than one substance (keep reading for a full explanation).
  • A Period: Thisrying (i.e. A larger amplitude means more energy). It is also controlled by the source of the wave rather than the medium itself because if you think about it, you can shake the rope on the floor with a wider motion to create a greater amplitude. Also, the amplitude in sound waves corresponds to the loudness.
  • A Wavelength: The length in meters of one standard sine curve unit in the wave (or the horizontal distance of one crest and one trough). The symbol for wavelength is the greek letter lambda (see a picture here). This can be manipulated by the source if the is the amount of time it takes for one wavelength to pass. It is in seconds, known as T, and controlled by the source.
  • A Frequency: This, f, is the amount of wavelengths that pass in a given amount of time. It can be found using the equation f=1/T. Because the unit is 1/s or s^-1, frequency is in Hertz (Hz). It is controlled by the source (you can picture shaking the rope more quickly, in effect changing the period, to cause more wavelengths to pass a certain point in a given amount of time). In terms of sound, frequency is referred to as the pitch.
  • A Velocity: This is the rate at which the wave moves, and is in m/s. Known as v, it is controlled by the medium. Velocity is equal to the amount of distance covered over time; since the wave can be seen as traveling horizontally, v represents a horizontal distance over an amount of time. This means v=lambda/T, or lambda x 1/T or f(lambda). This relationship explains why lambda is controlled by both the source and the medium: if the medium is held constant and the frequency is changed, lambda changes. If f is held constant but the wave travels through many media, lambda also must change. It is also good to know that sound waves travel at approximately 330 m/s in air.

That certainly was a lot! But now you have a solid understanding of the wave. Note: All quotations on this page are from Mr. GK.


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