Review of Mechanical Waves Test Wednesday!

The Timing of Waves Have you ever listened to the waves of the ocean? If you have, you know there is a rhythm to it. The waves seem to be almost evenly spaced.

The Timing of Waves When a wave completes the motion that returns it to its starting position= 1 cycle. Cycle= one up and one down

How to Time of Waves –We can see how much time is required for one cycle. –We can see how many cycles happen in a certain amount of time.

The Timing of Waves Period - the time required for one cycle. –Measured in seconds (or some unit of time) Frequency - the number of complete cycles in a given time. –Measured in cycles per second (“hertz” Hz) Frequency = 1 / Period

What if… What if you shook a rope up and down once a second… what would the frequency of the wave be? 1 cycle per second, 1 hertz What if you shook a rope up and down twice a second… what would the frequency of the wave be? 2 cycles per second, 2 hertz

Vibration and Frequency Note that however fast you vibrate something, that’s how fast the thing will vibrate. This helps us understand more about frequency. Example: Ruler on a desk

Vibration and Frequency A wave’s frequency equals the frequency of the vibrating source producing the wave. If you shake a rope up and down twice in a second, you expect the wave to also go up and down twice a second.

Wavelength Not only can we look at the time-factors of a wave; we can look at the length of a wave. Wavelength is the distance between a point on one wave and the same point on the next cycle of the wave.

Wavelength You can measure it between adjacent crests or between adjacent troughs. Or you can measure it between adjacent compressions or rarefactions.

Wavelength Wavelength and frequency are inversely related. When one gets larger, the other gets smaller. When the wavelength is shorter, crests are closer together. If crests are closer together, you can go through more cycles in a given amount of time (more frequency). Increasing the frequency of a wave decreases its wavelength.

Wave Speed Recall, speed is how much distance you cover in a certain amount of time. Consider 1 cycle: –It covers one wavelength of distance –It takes one period worth of time Speed = wavelength / period = wavelength x frequency

Amplitude We have seen that we can describe waves by time (period or frequency), distance (wavelength) and speed. We can also describe how big a wave is.

Amplitude If you drop a pebble into a pond, the wave is not very high. If you drop a cannonball into a pond, the wave will be higher. We say these different waves have different amplitudes.

Amplitude The amplitude of a wave is the maximum displacement of the medium from is rest position. –In English… amplitude is how big the wave is.

Amplitude Which is harder: –Shaking a rope up and down a little –Or shaking a rope up and down a lot The more energy a wave has, the greater its amplitude.

Properties of Waves: (you need to know these!) PeriodFrequency WavelengthSpeed Amplitude