In this lesson our instructor talks about sound. First, he discusses the speed of sound, pitch, intensity, and decibels. Then he talks about loudness and some examples. He also lectures on beats and sonic boom. Four complete example problems round up this lesson.
Sound waves are transmitted as a series of longitudinal pressure differentials.
Depending on the medium and its specific conditions, the speed of sound can vary greatly.
"High" pitches correlate to high frequency sound waves, "low" pitches correlate to low frequency sound waves.
The intensity ("loudness") of a sound is determined by the power (P) of the source and the area (A) it is spread over:
If the source of the sound spreads perfectly evenly in all direction (which turns out to be difficult in the real world), we can model it with a sphere. The surface area of a sphere is A=4πr2, which we can use with the above equation.
The human ear can hear a huge variety of intensities. We manage this issue by introducing a logarithmic scale for measuring intensity: the decibel (dB).
If you feel uncomfortable with logarithms, you might want to do a quick review of how they work. Check out the pre-calculus math section on Educator.com to get refreshed with logs.
We define the idea of sound level (β) using decibels:
β = (10 dB) ·log10
Since waves can interfere with one another, if they have different frequencies, the waves will come in an out of phase with each other. This is the beat frequency:
fbeat = |f1 − f2|.
For objects traveling faster than the speed of sound, we can describe its speed with a Mach number: [v/(vs)]. Mach 1 is the speed of sound, Mach 2 is twice the speed of sound, etc.
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.
This book includes a set of features such as Analyzing-Multiple-Concept Problems, Check Your Understanding, Concepts & Calculations, and Concepts at a Glance. This helps the reader to first identify the physics concepts, then associate the appropriate mathematical equations, and finally to work out an algebraic solution.