Chapter 15 Sound. Quiz 15. Chapter 15 Sound. Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves Solve problems relating the frequency, wavelength, and velocity of sound
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The danger of earthquakes is the transfer of energy. The ground particles of the earth rarely travel more than 1.5m themselves (same with thunder, the air particles travel less than a meter), but the transfer of energy still occurs.
There is also a Doppler effect for light. Instead of a sound source, there is a light source. An increase in frequency is called a blue shift. The frequency is shifted towards the ultraviolet (higher energy, higher frequency).
A decrease in frequency is called a red shift. The frequency is shifted towards the infra red (a lower frequency, lower energy).
Far stars and galaxies, as we observe them, show these shifts as they move closer and farther from us. It is this shift (a measurement of it) that allows astronomers to calculate the speed at which they are moving relative to us. A star that spins fast enough has both a red and blue shift. The side turning away from us has a red shift and a blue shift on the side turning toward us. This allows us to calculate the speed of the spinning star.
Police radar is able to tell our speed by doing calculations of frequency. The antenna of the police car sends out a signal (with a certain frequency). Then when the wave gets reflected back, it has a frequency shift based off of how fast the car was moving. That is how radar works.
Illegal devices send out the same wave out of phase…
Sonic Boom: Objects moving faster than the wave speed
When an object (usually planes) flies faster than the speed of sound, the crests pile up and produce a cone shaped shock wave. There are two shock waves, one at the front of the object, one at the back of the object.
It produces an “N” shaped wave, called this because of the N shaped graph of pressure. Initially, the pressure builds up at the front, at the nose of the plane, where all the molecules are crunched together. Then it decreases linearly across the plane, and finally jumps back up as the molecules fly back to fill the hole left by the plane.
The pressure change is not very large at all, just 50 – 500 Pascals.
The danger and damage is caused by how fast this occurs. For military planes, this change occurs in 0.1 s or less and for the space shuttle in about 0.5 s. Due to the small interval, only one sonic boom is heard from small military fighters, but two can be heard by the space shuttle. The pressure changes can even cause physical damage to buildings.
Prey fight back as well. Moths (as well as some other prey) can also detect these emitted waves. Upon hearing the waves, they drop to the ground and collapse their wings (to minimize their surface area). Also moths tend to be slightly furry, this helps absorb some of the energy of the wave and reflect the wave back at smaller intensities.