Chapter 1, Section 2 Properties of Waves

Chapter 1, Section 2 ­ Properties of Waves Introduction One of the most elegant and graceful Olympic sports is rhythmic gymnastics. A ribbon dancer flicks a stick attached to a ribbon, making waves that travel down the ribbon. Some of the waves are longer, while others are shorter. The rate at which the gymnast flicks her hands affects both the length and shape of the waves in the ribbon. This is just one of many different kinds of waves. Waves can carry a little energy or a lot. They can be short or long. They can be rare or frequent. They can travel fast or slow. All waves, however, share certain properties.​
The basic properties of waves are amplitude, wavelength, frequency, and speed. Amplitude Some crests are very high, while others are very low. The distance the medium rises depends on the amplitude of the wave. ​
Amplitude​
is the maximum distance that the particles of the medium carrying the wave move away from their rest positions. For example, the amplitude of a water wave is the maximum distance a water particle moves above or below the surface level of calm water. You can increase the amplitude of a wave in a rope by moving your hand up and down a greater distance. To do this, you have to use more energy. This energy is transferred to the rope. Thus, the more energy a wave has, the greater its amplitude. Amplitude of Transverse Waves As shown in the picture, the amplitude of a transverse wave is the maximum distance the medium moves up or down from its rest position. You can find the amplitude of a transverse wave by measuring the distance from the rest position to a crest or to a trough. Amplitude of Longitudinal Waves The amplitude of a longitudinal wave is a measure of how compressed or rarefied the medium becomes. A high­energy wave causes more compression and rarefaction than a low­energy wave. When the compressions are dense, it means that the wave’s amplitude is large. Wavelength A wave travels a certain distance before it starts to repeat. The distance between two corresponding parts of a wave is its ​
wavelength​
.​
You can find the wavelength of a transverse wave by measuring the distance from crest to crest, as shown in the picture above. Or you could measure from trough to trough. The wavelength of a longitudinal wave is the distance between compressions. Frequency Wave ​
frequency​
is the number of complete waves that pass a given point in a certain amount of time. For example, if you make waves on a rope so that one wave passes by every second, the frequency is 1 wave per second. How can you increase the frequency? Simply move your hand up and down more quickly, perhaps two or three times per second. To decrease the frequency, move your hand up and down more slowly. Frequency is measured in units called ​
hertz​
(Hz). A wave that occurs every second has a frequency of 1 Hz. If two waves pass you every second, then the frequency of the wave is 2 per second, or 2 hertz. The hertz was named after Heinrich Hertz, the German scientist who discovered radio waves.