Unit 9: Continued

Today we covered more about waves and learned about natural frequency. As I mentioned in my last post, sound is a longitudinal wave that needs a medium. We learned today that light travels faster than sound. It takes five seconds for every mile sound needs to travel. A good example of this would be thunder and lightning. The speed of sound can be used in an equation. The velocity of sound is represented by Vs and Tc is the temperature in Celsius. Vs=331m/s+Tc(0.6)
We also leaned about the human hearing range. We can hear from 20KHz, or 20,000Hz, to 20Hz. Anything above 20,000 Hz is considered ultrasonic and anything below 20Hz is considered infrasonic. As we age, our hearing ability decreases. To decrease the possibility of being deaf at an early age, we should avoid listening to music at a loud volume.

Some cool information about thunder & lighting:
"The time between seeing a lightning flash and hearing the thunder it produces is a rough guide to how far away the lightning was. Normally, thunder can be heard up to 10 miles from the lightning that makes it. Lightning heats the air around it to as much as 60,000 degrees, producing sound waves by the quick expansion of the heated air. Since light travels at 186,000 miles per second, you see the lightning the instant it flashes. But sound, including thunder, travels about a mile in five seconds near the ground. If 15 seconds elapse between seeing a lightning bolt and hearing its thunder, the lightning was about three miles away. Lightning closer than about three miles away is a warning to take shelter immediately. Successive lightning strikes are often two to three miles apart. If the first stroke is three miles away, the next one could hit you." 
Source: http://www.usatoday.com/weather/wlight1.htm


A couple vocabulary terms:
Natural frequency is the frequency at which an object wants to vibrate.

Resonance is the overall adding of wave energies.

Photo:
Nikon D3000
f/5.6   ISO 100   20.0 exposure
5/2/11