Physical Science - Waves

• Words that can proceed the word 'wave'

  • Ocean
  • Radio
  • Micro
  • Transverse
  • Longitudinal
  • Mechanical
  • Electromagnetic
• When a stone is thrown into a pond, it creates ripples on the surface of the water
• A leaf resting on the surface will bob up and down, back and forth as each ripple/wave disturbs it. But when the wave passes, the leaf will return to its original position (or there abouts)
• Individual water drops do NOT travel with the wave, they move only slightly. ENERGY DOES
• The location of the individuals does NOT move with the wave, only ENERGY moves with the wave
• Wave


  A periodic disturbance in a solid, liquid or gas as ENERGY is transmitted through the medium
• Medium


  • A physical environment in which phenomena occur
  • The matter through which a wave travels
• Mechanical Wave


  • A wave that requires a medium
  • Can NOT travel through a vacuum
  • Almost ALL waves
• Electromagnetic Wave


  • Can travel across EMPTY space
  • Does NOT require a medium
  • Consists of changes of ELECTRIC and MAGNETIC fields in space
  • Visible light and RADIO waves are just 2 examples
• Waves


  • Waves transfer energy
  • Waves can do work (because work is the transfer of energy)
  • Sound waves do work on your ear drum
  • Light waves do work on your eyes
• Waves


  • A pebble is dropped into a pond, the leaf may move 1 cm
  • A rock is dropped into a pond, the leaf may move 3 cm
  • A Boat moves though the pond, the waves may move the leaf 1 meter
• WAVE MOTION TRANSFERS ONLY ENERGY, NOT MATTER
• Mechanical waves are transferred by the motion of particles, but NO MATTER is transferred
• As a wave travels, energy may spread out
• Ear drum

  • It actually gets "beat" like a drum
  • The atoms in the air vibrate and "beat on your ear drum"
  • When the vocal chords, or speakers move, it causes particles in the air to vibrate, in doing so that vibration will continue affecting atoms in the air until the vibration reaches your ear drum
  • The vibrations are then read and triggers a series of "electrical pulses" to your brain, where they are interpreted into sounds
• Mechanical waves

  • Spread out through the medium evenly and sphereically from the source, if the area is open in ALL directions
  • The stronger wave will be in the direction of the source
• Longitudinal Wave

  A wave in which the particles of the medium vibrate parallel to the direction of the wave motion
• Transverse Wave

  A wave in which the particles of the medium move perpendicular to the direction of the wave motion
• Types of Waves


  • Visible light waves
  • Radio waves
  • X-rays
  • Water waves
  • Rope waves
  • Some earthquake waves
  • Sound waves
  • Some earthquake waves
• Crest

  The highest point of the wave
• Trough


  The lowest point of the wave
• Amplitude


  • The maximum distance that the particles of a wave's medium vibrate from their rest position
  • Half the vertical distance between crest and trough
  • More ENERGY = Bigger Amplitude
• Compression

  Crowded areas, comparable to crests
• Rarefaction

  Stretched out areas, comparable to troughs
• Wavelength

  • The distance from any point on a wave to an identical point on the next wave
  • Represented by greek symbol lambda (λ)
  • From CREST to CREST or TROUGH to TROUGH
  • Units: meters
• Period


  • The time it takes a complete cycle or wave oscillation to occur
  • The time it takes for 1 wavelength to pass a specific point
  • Expressed in seconds
• Frequency


  • The number of full wavelengths that pass a point in a given time interval
  • Measured in hertz (Hz)
  • f = 1/T
• Electromagnetic Spectrum


  • The part of the spectrum that is visible to the naked eye is called visible light
  • It ranges from Infared to ultraviolet
  • Infared has a long wavelength, where ultraviolet has a short wavelength
  • Electromagnetic waves also exist at other frequencies
• Wave Speed


  • How fast a wave moves
  • v = d/t
  • For a wave it is convenient to use the wavelength as the distance traveled
  • The amount of time it takes for 1 wavelength is a period
  • v = λ/T
  • v = f x λ
• Wave Speed

  • Speed depends on medium
  • In gases, the molecules are far apart and move randomly, therefore the wave must travel through a lot of empty space before "bumping" into another particle
  • In liquids, such as water, the molecules are much closer together, but they are still free to slide past one another
  • In solids, molecules are not close together, but are tightly bound, when 1 mass vibrates, all of the particles vibrate, this causes MECHANICAL waves to travel very quickly through solids
• Pitch


  • How high or low the sound is
  • Determined by the frequency at which the wave hits the ear drum
  • High Pitch = High frequency
  • Low Pitch = Low frequency
• Sound waves spread out evenly in a 360 degree direction when the source is stationary
• Doppler Effect


  An observed change in the frequency of a wave when the source or observer is moving
• When the source of the sound is moving, the waves (in the direction of the movement) get compressed, increasing the frequency, increasing the pitch
• As the object's speed increases, the frequency of the wave hitting the ear increases, and therefore, the pitch increases
• Just as the waves were compressed due to movement of the source, the waves left behind are more spread out, causing the frequency to be much lower and therefore the pitch is lower
• Reflection


  The bouncing back of a ray of light, sound, or heat when the ray hits a surface that it doesn't go through
• Reflection at a fixed barrier


  The REFLECTED WAVE TRAVELS in the opposite direction and is turned upside-down
• Reflection at a free barrier

  The REFLECTED WAVE TRAVELS in the opposite direction as the original wave
• Diffraction


  A change in the direction of a wave when it finds an obstacle or an edge, such as an opening