PHYS 012A Lecture Notes - Lecture 1: Transverse Wave, Longitudinal Wave, Wind Wave
12 Jun 2018
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Chapter 16: Wave Motion 9/6/17
Types of Waves
- Ex of a wave
o A pele hits the water’s surfae
o Resulting circular wave outward from the creation point.
Two main types of Waves
- Mechanical waves
o Some physical medium (like a string) is being disturbed.
o The wave is a propagation of a disturbance through a medium
- Electromagnetic waves
o No medium required
o Ex: light, radio waves, x-rays
General Features of Waves
- In wave motion, energy is transferred over a distance
- Matter is not transferred over distance. (The motion moves you)
- Some physical mechanism through which elements of the medium can influence each other.
Pulse on a String
- The wave is generated by a flick on one end of the string. The string is under tension. A
single bump is formed and travels along the strig. That’s a pulse. Had is the soure of
disturbance and the string is the medium.
Transverse Wave (moving a slinky up and down)
- A wave is a periodic disturbance travelling through a medium.
- A traveling wave or pulse that causes the elements of the disturbed medium to move
perpendicular to the direction of propagation is called a transverse wave.
Longitudinal Wave (moving a slinky left and right by pushing it)
- A traveling wave or pulse that causes the elements of the disturbed medium to move
parallel to the direction of propagation is called a longitudinal wave. Ex: sound wave.
- The displacement of the coils is parallel to the propagation.
Complex Waves
- Some waves exhibit a combo of transverse and longitudinal waves.
- Surface water waves are an example.
o The elements of water at the surface move in nearly circular paths.
o The disturbance has both transverse and longitudinal components.
o Crest is the high pint and the trough is the low point.
- Example: Earthquake waves (recorded by seismographs in many locations that help pinpoint
earthquake location)
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o P waves - P stads for priary, also is logitudial – tectonic plates shift - Fastest
at 7-8 km/s
o S waves - “ stads for secondary, also is transverse – plates would spread out -
Slower at 4-5 km/s
Traveling Pulse
- Represented by wave function, y(x,0) = f(x)
If the pulse begins to move
- The speed of the pulse is v.
- At some time, t, the pulse has traveled at a distance vt.
- Vertical position is now y = f(x-vt)
0
For a right movement:
At t=0, y(x,0) = f(x) At time t: y(x,t) = f(x-vt)
(Negative velocity so the sign becomes positive) For a left movement:
At time t: y(x,t) = f(x+vt)
Sinusoidal Waves
- The wave represented by the curve shown is the sinusoidal wave.
- It is the same curve as sin theta plotted against theta and can build more complex waves.
- As a wave moves towards the right, it will change position.
- Each element moves up and down in harmonic motion, but it looks like it is completely
changing position.
- Must know the difference of the motion of the wave and the motion of the elements of the
medium.
find more resources at oneclass.com
find more resources at oneclass.com
