Course:     8th grade Physics

Unit Introduction: Waves

Waves have measurable properties such as speed, amplitude, frequency, and wavelength.  In Part 1, students learned that changing the medium affects the speed and wavelength of waves.  In Part 2, students continue their study of how changes in the medium (density, depth, tension) affect wave properties.  In Part 3, students continue their exploration of wave properties by investigating what happens when waves collide with each other or pass through a barrier.  Students also study how energy from sound waves transfer to other objects and the affect the transfer has on the sound that is heard.

Objectives: Students will learn…

Part 1:

  1. Amplitude can be determined by measuring the maximum displacement of the medium for a mechanical wave. 
  2. Our ear interprets amplitude of a sound wave as loudness.
  3. Frequency can be found by measuring the number of waves created or passing a marker per time period.  Frequency of a sound wave is interpreted by our ears as pitch.
  4. Wavelength is the distance between two positions on a wave with the same displacement, heading the same way.
  5. Speed, frequency and wavelength are independent of amplitude.  Changing the frequency of a wave changes its wavelength inversely. 
  6. Waves can change direction when they hit a boundary.  If the boundary is rigid, the pulse will switch sides (phase inversion).  If the boundary is flexible, the pulse is reflected on the same side (same phase) as the incoming wave. 
  7. Speed can be determined by dividing the distance a pulse travels by the time it takes to travel that distance.  Changing the medium or the tension in the medium changes the speed of the wave.
  8. Frequency = wave speed/ wavelength.
  9. Waves can change direction when they hit a boundary.  If a pulse strikes the boundary at an angle, the incoming angle is equal to the reflected angle.

4.    Sound sources are vibrating objects.  Waves transfer the energy from the vibration.  The length of the vibrating material determines the frequency produced.

Part 2:

  1. Sound waves travel at a measurable speed that is not affected by the amplitude or frequency of the wave.
  2. The speed of sound affected by the type of medium in which it travels.       
  3. The speed and wavelength of a wave is affected by the type of medium in which it travels. 
  4. Increasing the tension in a spring causes waves to travel faster, which affects the wavelength.
  5. Sounds travel faster at higher temperatures.  Temperature affects the wavelength of the sound.
  6. Detect an apparent change in frequency when the source of a wave is in motion relative to the observer.
  7. Detect an apparent change in frequency when the observer is in motion relative to the source of the sound.
  8. Water of different depths cause waves to travel at different speeds. 
  9. When a wave reaches a boundary at an angle and passes into a medium where the speed changes, the wave direction changes or refracts.

Part 3:

  1. When pulses encounter each other their amplitudes add creating constructive and destructive interference.       
  2. When waves of different frequencies come together beats occur.  This can be quantified by the equation Beat Frequency = | frequency1 – frequency2|. 
  3. Wave energy can pass through each other undisturbed.
  4. Every point on a wave front can be viewed as a point source for the next wave front.
  5. Wave energy can spread behind a barrier in a medium.
  6. Vibrations can be transmitted when a vibrating object touches another object.  The larger the area of vibration the louder the sound. When two objects have close natural frequencies, vibrating one can cause the second to vibrate even when they are not in direct contact. This is known as resonance.