April 14 – April 15

What is the definition of a wave? Example: Sound from a speaker traveling through air to my ear. All waves ‘travel’ or carry energy from one location to another until the wave encounters some sort of barrier or new medium. What happens then? Depending on the barrier / new medium, some of the wave energy may transmit through. But some of the wave energy will be reflected. A disturbance that carries energy without transferring matter

A great example of wave reflection and the interesting patterns that result from it are waves on a string/slinky. Because the string has a short length, the wave quickly runs into a barrier and reflects backward.. Example: Rope attached to a fixed point. A wave pulse travels to the end and reflects back. Slinky Demo! What would happen if I increased the rate of the pulses? The original and reflected waves would interfere, creating odd patterns. Are the original and reflected waves still traveling through the medium? Yes! It just doesn’t look like it because we see the sum of their behavior.

If we vibrate the string at exactly the right frequency, we can create standing waves. Standing waves have points – called nodes – that appear to ‘stand still’. Standing waves result from the interference of two identical waves with the same frequency and the same amplitude traveling in opposite direction – such as we get with reflected waves (of certain frequencies) along a string.. Antinode – maximal displacement node –zero displacement

By adjusting the frequency of disturbance, standing waves of different wavelengths can be generated. The production of standing waves is how tones are generated in most instruments (strings, winds, brass, etc.)!. Slinky Demo! Fundamental tone (first harmonic) Second harmonic Third harmonic

What wavelengths can be produced? Only regular divisions of the string …. Note that the fundamental frequency has half a wavelength (one loop) across the string. In other words, it has 1 * ½ wave lengths. As we go up harmonics, we add ½ wavelengths.