Chapter 11

 

11.1          Wave Nature

Objective-        Describe a wave.

                        Explain mechanical waves.

Describe the types of mechanical waves.

                       

  1. Waves are repeating disturbances or movement that transfers energy through matter of space.
  2. Three examples are ocean waves, light, earthquake (seismic waves).
    1. Ocean waves disturb water and transfer energy through it.
    2. Earthquake (seismic) waves transfer energy through the Earth.
    3. Light travels through empty space and transfers energy from place to place.
  3. A wave will only exist as long as it has energy to carry. 
  4. All waves are produced by something that vibrates.
  5. The matter a wave travels through is called a medium.
    1. For sound waves, the medium is air.
    2. For ocean waves, the medium is water.
    3. Some waves like light and radio do not need a medium.
  6. Waves that travel through matter are called mechanical waves.
  7. There are 2 types of mechanical waves: transverse and compressional.
  8. In a transverse wave, matter moves back and forth at right angles to the direction the wave travels.

Examples: In a water wave the water moves up and down while the wave approaches the shore line.  With a rope, you move the rope up and down but the wave travels from you to the other person.

  1. In a compressional wave, matter moves back and forth in the same direction that the wave travels.

Examples:  In a slinky, when you stretch a slinky and let it go the slinky moves forward and the wave moves forward.  A sound wave is also a compressional wave because the sound travels most in the direction that you are speaking. 

  1. When discussing water waves, their size depends on 3 things:
    1. Wind speed
    2. The distance over which the wind blows
    3. How long the wind blows
  2. Seismic (Earthquake) waves are a combination of compressional and transverse waves.
  3.  Earthquakes produce three types of waves:
    1. primary (P) fastest moving and compressional
    2. secondary (S) moves through solids and transverse
    3. surface waves spread from epicenter both transverse and compressional

 

 

 

 

11.2          Wave Properties

Objective:         Identify and describe the parts of a wave.

                        Calculate wave speed.

                        Sketch, label, and describe a transverse and compressional wave.

 

  1. Wavelength is the distance between one point on a wave and the nearest point just like it. 
    1. λ (lambda) represents wavelength.
  2. Frequency is the number of wavelengths that pass a fixed point in a second
  3. Wavelength and frequency have an inverse relationship.
    1. When one increases, the other decreases.
  4. The speed of a wave is calculated  as wavelength times frequency.

a.  v = λ f             v                               v = m/s          λ = m     f  = hertz (hz)

                        λ      f                

      5.  Amplitude is related to the amount of energy in a wave (high amplitude greater

            energy).

 

In a transverse wave:

Crest    -           highest point on a wave

Trough -           lowest point on a wave

Wavelength -    from crest to crest or trough to trough

Frequency -      number of crests or wavelengths to pass a point per second

Amplitude -      from rest to crest or rest to trough

 

In a compressional wave:

Compression – more dense area (closer together)

Rarefaction -    less dense area (farther apart)

Wavelength – one compression and one rarefaction

Frequency -      number of compressions or rarefactions to pass a point per second

Amplitude – how tight the coils in a compression or how loose the coils in a rarefaction

 

11.3          Wave Behavior

Objective-        List and describe the 6 types of wave behavior.

                        Explain the Law of Reflection

  1. There are 6 types of wave behavior.
  2. Reflection is when a wave strikes a surface and bounces off of it.
  3. The law of reflection states that the angle of incidence equals the angle of reflection.
  4. Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to the next.
  5. The greater the change in speed, the greater the refraction.
    1. when speed decreases it refracts to the normal.
    2. When speed increases it refracts away from the normal.
    3. Objects underwater seem closer to the surface than they are.
  6. Diffraction occurs when an object causes a wave to change direction and bend around it.
  7. The amount of diffraction depends on the size of the obstacle compared to the wavelength.
  8. AM radio reception has longer wavelengths so they diffract around obstacles and have better reception around tall buildings and barriers.
  9. Interference is when two or more waves overlap and combine to from a new wave.
  10. The two types of interference are constructive and destructive.
    1. constructive -  add together
    2. destructive   -   subtract
  11. A standing wave has a special pattern when waves of equal wavelength and amplitude traveling in opposite directions continuously interfere with each other.
  12.  Resonance is the ability of an object to vibrate by absorbing energy at its natural frequency.