Noll turns up a speaker, and the cone on its front visibly shakes.
Earlier in the course you sorted waves into transverse and longitudinal, and you met compressions and rarefactions. The shaking cone shows which kind sound is.
The speaker cone swings forward and back.
Each forward swing squeezes the air just in front of the cone.
That squeezed region of air is a compression.
Each backward swing leaves a stretched region of air behind the squeeze: a rarefaction.
The compressions and rarefactions travel outward through the air, one after another.
That traveling pattern is the sound wave.
As the wave passes, the air's particles swing forward and back along the direction the sound travels: parallel to it.
A subwoofer plays a deep note under water in a test tank. Describe how the sound travels through the water.
The subwoofer cone squeezes the water in front of it, making a compression.
As the cone swings back, it leaves a stretched region: a rarefaction.
The compressions and rarefactions travel outward through the water.
The sound travels through the water as a longitudinal wave of compressions and rarefactions.
In a slow-motion close-up, the air near a buzzing speaker shows regions where the particles bunch together and regions where they spread out, moving away from the cone. Name the two kinds of region.
A region where the medium's particles are squeezed together is a compression.
A region where they are spread apart is a rarefaction.
The bunched regions are compressions, and the spread-out regions are rarefactions.
Sound from a siren crosses a parking lot through the air. How do the air's particles move as the wave passes?
In a sound wave crossing a gym, one region has the air's particles squeezed together. What is that region called?
Ottoline says: 'Sound is a longitudinal wave, because the medium's particles oscillate parallel to the direction the wave travels.' Is Ottoline correct?
Which statement describes how a clap's sound crosses a classroom?
A long steel fence rail carries the clang of a gate hinge. As the sound passes one point of the rail, what happens at that point?
Pim hums a note across a quiet room. Which statement about the sound crossing the room's air is correct?