Chapter 26 Study Guide

1. Air must vibrate in order to hear sound, but what must happen for air to do this?
2. For the average human to hear a sound what is the least number of times something can vibrate every second; what is the greatest number of times?
3. Sound ‘a’ has a higher pitch that sound ‘b’; which sound has the higher frequency?
4. What is the name given to air vibrations that are below the ability of humans to hear; what is the name given to air vibrations that are higher than those that can be heard by the average human?
5. Which has more pressure compressed air or rarified air?
6. Sound waves can pass through all of these except? gases, solids, liquids, and vacuum?
7. Why cannot sound pass through your choice from #6?
8. Which is more elastic: hot air or cold air? Which ‘kind’ of air can sound pass through more easily and therefore more rapidly?
9. What is the speed of sound in air? (N.B. Remember that this speed is approximate; so what speed does Mr. Hewitt give you as the average?
10. Sound travels ___ times faster in water and ___ times faster in steel.
11. Explain why sound travels faster in liquids and solids than it does in gases.
12. When a vibrating tuning fork is placed on a table top the sound is a lot louder. Explain why.
13. Try this when no one is around: drop a couple of pots and pans along with their lids and a knife, a fork and a spoon. Wow! What a lot of sound these things make! Now, drop each item one at a time. Why does each object have a completely different sound?
14. Look on page 395, section 26.7 and write both definitions for ‘natural frequency’ found at the end of the section.
15. Under what condition can one object force a vibration in another object?
16. Mr. Hewitt says that everything has a natural frequency, but some things are just way to difficult to vibrate. For example a sheet of tissue paper or a t-shirt are very difficult, if not impossible, to make vibrate. So, explain why things like t-shirts and tissue paper are so hard to make vibrate.
17. A piano has a soundboard, a harp has a soundboard, and violins and guitars have soundboards, what is the purpose of soundboard?
18. Consider your favorite radio station. For example you might like AM 600. The ‘600’ is really 600 thousand vibrations per second! So, can you figure out what you are actually doing when you ‘tune’ in a radio station?
19. You saw waves interfere on the spring; can sound waves also interfere with each other?
20. Take a look at figure 26.14. One of these guys will hear a loud sound and the other will hear practically nothing. Which is which?
21. Jackhammers are very, very loud. How can sound engineers using equally loud sounds from a microphone, take advantage of the principle of destructive interference to nearly completely silence a loud jackhammer?
22. If two waves of different wavelengths are superimposed on each other what kind of interference will be produced?
23. The type of interference mentioned in #21 will produce beats. If the frequencies of the two waves differ by, say, 5 Hz, how many beats per second will be heard? If the frequency of one of the waves is 440 Hz, what are the two possible frequencies of the other sound source?
24. Explain how it is possible for a person to tell from what direction a sound is coming from.
25. Note the figure below.
1. How many decibels is the threshold of hearing?
2. How many decibels is the threshold of pain?
3. How many decibels is a quiet living room in a typical home?
4. A sound that is ten decibels louder than another sound is perceived as twice as loud. A sound that is 20 decibels louder than another sound is _____ as loud.
5. How much louder is a normal conversation than a whisper?