Lecture 9: Mechanical Waves: wavelength, frequency, speed

Mechanical Waves

• Wave is a periodic disturbance in space and time that has ability to propagate.

• Mechanical wave is a propagating disturbance in position of elements of some substance, a medium

Different type of waves

• Longitudinal wave - motion of particles is parallel to the direction of wave propagation
  Notice: particles move back and forth, without any net displacement, but crests travel. Wave motion does not transport matter over any significant distance ! But it does transport energy
• Transverse waves - motion of the particles are transverse to the direction of wave propagation Notice, waves propagate with specific velocity, which seems determined only by the properties of the medium.
• Some waves are complex. For example in ocean surface waves water elements move in circles - combination of longitudinal and transverse motion.
  

Periodic Wave: wave length, frequency, amplitude and speed

Let us look at a very useful applet in our textbook.

• In Periodic wave each particle experience simple harmonic oscillation, but the phase of oscillation is shifted from place to place.
• Amplitude A : largest disturbance of a particle, height of crests
• Wave length λ: distance between crests (or between troughs)
• Freguency f : frequency of oscillation of a particle (same for all of them). ω = 2 π f
• wave speed v : speed of displacement of the crests.

We observed that:

• Speed of simple periodic wave does not depend on frequency, wavelength or amplitude
• Longer the wavelength, lower the frequency matter particles oscillate with
• Shorter the wavelength, higher the frequency, indeed