One Chapter 7

• There are two ways that energy can be transferred:
  • particle motion.
  • waves.
• With waves, no physical body moves from place to place.
• Wave - The propagation of energy from place to place as a result of vibratory motion. Also, a wave may also be considered to be a transfer of energy in the form of a disturbance.
  • Two types of waves exist:
    • Mechanical Wave - Waves that move through a medium. Physical bodies vibrate in the medium as the wave passes by.
    • Electromagnetic waves - Waves that consist of alternating electric and magnetic fields. No physical bodies vibrate.
• The wave source is usually a vibrating or oscillating object which often displays Simple Harmonic Motion (To be defined later).
• The energy of the wave comes from the energy of the source.
• There are two types of motion we must talk about in order to understand waves.
  • Vibratory motion - The motion of the source and particles in the medium.
  • Wave Motion
• The terminology used for each is similar.

• Periodic motion - The repetition of a motion.
• e.g. bouncing of a weight hung on a spring.
  • Usually there is the same time interval between motions.
  • specific to vibratory motion.
• Periodic waves - waves in which the motions of the medium is repeated at regular time intervals.
• Pulse - A wave which consists of a single disturbance of the medium (shock wave). E.G. Tsunami.
• Medium - The material through which a wave travels.
  • The medium does not move from place to place, only the energy. The particles of the medium display vibratory motion.
• Cycle - One complete oscillation.
• Oscillation - One complete path.
• Frequency - The number of cycles per second. This definition applies to oscillating objects.
• Frequency of a wave - The number of phases of a wave that pass a given point in a medium per unit of time.
  • The frequency of a wave is the same as the frequency of the source of a wave.
• Phase of a wave - The pointed out part of a wave that has a given position of the medium and velocity of the medium.
• Period - The time required for one cycle.
  • applies to oscillating objects.
• Period of a wave - The time it takes a wave to travel one wavelength.
• Wavelength - The distance between successive in phase points on a wave.
• In phase - Points of a wave, or positions of an oscillating object, that have the same phase.
• Phase of a vibrating object - The pointed out location of the object specified by position and velocity.
• Amplitude - The distance in either direction from the equilibrium position to the maximum displacement.
• Equilibrium position - The position of the object (for vibratory motion) or the medium (for waves) when no vibration or wave is present.
• It should be noted that the units of frequency are a number per unit of time.
  • The most common unit is the Hertz (Hz) which is a number per second.
• The units of period are units of time (the second is the most common).
• Formula which are important for waves are:

• Besides being mechanical or electromagnetic, waves can be:
  • transverse waves
  • longitudinal waves
• Transverse waves - Waves in which the particles in the medium vibrate perpendicular to the direction of energy transfer. An example would be water waves.
• Longitudinal waves - Waves in which the particles in the medium vibrate parallel to the direction of energy transfer. An example would be sound waves.
• Transverse waves have different parts than longitudinal waves
  • Transverse waves have:
    • crests
    • troughs
  • Longitudinal waves have:
    • compressions
    • rarefactions
• Crest - The region of a transverse wave with the maximum positive displacement of the medium.
• Trough - The region of a transverse wave with the maximum negative displacement of the medium.
• Positive pulse - A crest.
• Negative pulse - A trough.

• For periodic waves, crests and troughs have equal lengths.
• Compression - The regions of a longitudinal wave where the particles of the medium are closer together than normal
• Rarefaction - The regions of a longitudinal wave where the particles of the medium are further apart than normal.

• For both waves and vibrating objects, energy may be lost due to friction.
  • In this case, amplitude decreases with time.
• Damping - the reduction in amplitude due to the loss of energy due to friction

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November 5, 2013