An ocean wave is a progressive wave - the crest of the wave moves across the water, all areas of the water will move up and then down again. For a standing wave, a node is a
Read chapter 19, do you have any questions?
What is the relationship between the volume of an echo and the volume of the original sound?
Why do low frequencies travel further than high frequencies?
Why does sound travel faster in warm air?
suppose all these waves have the same frequency. Which has a longer wavelength?
sound from source a has twice the frequency of sound from source b. Compare the wavelengths of the two sounds.
Define the word "rarefaction".
recall the feeling of being pushed on a swing by older cousins. You have a highly competent cousin pushing you. You swing higher and higher and higher. That cousin is called away and is replaced with a much less competent cousin. You are no longer swinging higher and higher. Explain what it is the less competent cousin does wrong.
if you described the motion of you swinging as a wave form, how high you are swinging is your
The perfect swing-pusher
Watch this video on resonant frequency . do you have any questions?
you may have heard of the tacoma narrows bridge, wind hit the bridge, breaking into a wave-like pattern. That pattern matched the natural frequency of the bridge and acted as a competent cousin pushing a kid on a swing. this is what happened. What do you wonder about this event?
in 1831, a regiment of british soldiers marched across a suspension bridge, which collapsed underneath them dropping about 40 soldiers into the river below. None were killed, but several were severely injured. The British army (and this is now standard regulation around the world) instituted a policy that any military parade will "break step" across a bridge. What do you think "break step" means, and why was this instituted?
take a plate and cover it with water. tap your right index finger in the water creating a wave pattern in the water. Describe the wave pattern.
now start tapping with both your right and your left index finger on different sides of the plate. watch how the wave patterns interfere with each other. Describe the wave patterns.
We talked in class about two waves interfering with each other to create a standing wave. This happens when the two waves that are interacting are
Why can you not create a standing wave with just any wavelength?
take a phone or some other device to play music (not a full fledged speaker). go into a kitchen or bathroom, or some other area with hard, tiled surfaces. place the phone on a counter with the phone speaker facing you. observe how loud the music is. Now take the phone and face the speaker towards the hard corner. What do you observe about the volume of the music?
walk around in an arc around your phone as best you can. Do you hear any variation in the volume of your speaker? it may help to have your speaker generating a pure tone rather than actual music.
Same thing, but instead of finding a hard surface in a kitchen or bathroom, find a soft corner, like a curtained window, or a corner of a couch. What do you observe?
Whats the difference?