Waves Lecture 7

# Waves Lecture 7 - Waves are everywhere Earthquake vibrating...

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Waves are everywhere: Earthquake, vibrating strings of a guitar, light from the sun; a wave of heat, of bad luck, of madnesselipsis Some waves are man-made: radio waves, stadium waves, microwaves, annoying sound waves of a physics lectureelipsis amplified by the electronics and loudspeakerselipsis Something moving, passing by, bringing a change and then going away, sometimes without a traceelipsis

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Mechanical waves require Some source of disturbance A medium that can be mechanically disturbed Some mechanism through which adjacent regions of the medium influence each other All waves carry energy and momentum A wave is a traveling disturbance that transports energy but not matter. The stadium "wave" travels all around the stadium. None of the fans travel around the stadium. They only stand up and sit down.
Well, let’s forget about humans and talk about passively floating objects and the impact the waves make on themelipsis. The buoy and the seal are going to bob on the waves and its motion can we well described by a harmonic oscillation. Imagine, you are a happy seal on a buoy. It is nicely warm and you closed your eyes. What kind of motion are you going to experience? Any way to find out that you are actually in sea rather than on a shaking platform?

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NO! An observer recording motion in a single point in space only sees a harmonic oscillation and there is no way to know, whether or not there are waves. How can he find out that he is shaking on waves? To look out and take a photograph (or to see what happens around him). The complex nature of a wave: it is an oscillation in time and a wavy pattern in space! Let’s do the oscillation part first. Oscillations have amplitude and frequency. Any way to measure them without looking out? You can measure frequency and accelerationelipsis And use them to derive the amplitude.
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