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### Course: Cosmology and astronomy>Unit 3

Lesson 2: Seismic waves and how we know earth's structure

# Refraction of seismic waves

Refraction of Seismic Waves. Created by Sal Khan.

## Want to join the conversation?

• When P-Waves get on the side of the earth opposite to the side they came from, wouldn't they start refracting the other way since the material that they are going through is now getting less dense?
• Not sure about "major changes have already occured". Why isn't the refraction symmetric? (it would refract the same amount coming up the same amount it refracted on the way down).
• Would the car not travel to the right? The front left wheel enters the denser medium first, so it travels slower while the other wheels in the less dense medium move faster. Wouldn't this make it move right?
• I was confused about this as well, until I watched these videos again. Apparently a P-wave moves faster in denser material, therefore as it moves down it curves to the left.
• Regarding your last contextualisation where the earth is simply denser in the center, why don't the waves get an inverted refraction (fast to slow) at the end of its curve when it gets from denser material (center of the earth) to lighter material (outer crust) ? Is it because they reach a stable motion, perpendicular to the layers?
• I am slightly confused in the fact that waves travel faster in material that is more dense. This seems to be counter-intuitive. Can anyone explain more clearly how this happens?
• At around , Sal said that the seismic waves would go in a curve if in a particular angle. But won't the seismic waves eventually material that isn't that dense (the crust)? Which would mean that the the waves wouldn't go the way Sal actually mentioned?
• Technically speaking yes, Sal just simplified it so that we could understand the physics of it.
(1 vote)

• What would happen if the car traveled down the center of the fast and slow medium? Which way would it turn?
• in the direction of the slow medium because the wheels on the fast medium are going faster turning the car in the direction of the slow medium. (more at )
• you show the example if you have a slow medium and a fast medium, but what if you have a (wait for it) ..... medium medium!