I. Waves Transfer Energy
- Water waves disturbance at one spot will cause things to move up & down at another location. This demonstrates a Transfer of Energy from one place to another- Sound Waves - vibrating object moves the air & the moving air vibrates eardrum.
- Earthquakes: Waves can create allot of damage!
II. Oscillating Motion
- Simple Harmonic Motion: Motion that repeats itself in a time consistent manner.- Pendulum: Cyclical motion where the time for the motion to repeat depends upon the pendulum length
- Mass and Spring: Time for repeating motion depends upon the length of the spring and the weight of the hanging mass.
III. Properties of Waves
- Pendulum motion traced out in time produces a sine curve- Has periodicity (s), The period , T, is the time it takes for the wave to reproduce itself
- Frequency - how many oscillations go past a point each second (cycles per second (1/s) or Hertz (Hz)) f=1/T
- Waves traveling have a wave speed. (meters per second or m/s)
- Wavelength (in meters) The physical length of the wave
- Traveling Wave Relationship: (velocity)=(frequency)(wavelength)
IV. Types of Traveling Waves
-Transverse Waves: Wave propagate perpendicular to the motion of the oscillation .-Longitudnal Wave: Wave propagate paralell to the motion of the oscillation .
V. Waves Can Interact - Superposition. Destructive & Constructive Interference
-When Two waves interact they can constructively add together or destructively cancel each other.- Interference: This is a wave property.
VI. Standing Waves
- Wave Reflection from a Boundary. A string with a fixed end reflects a wave. The wave inverts upon reflection.-Standing Wave: Reflected waves add to incident waves. At precise frequencies the waves add together producing nodes (areas of no vibration) and antidnodes (vibrating bumps).
- Important phenomena we will come back to when studying sound resonance and musical instruments.
VII. Doppler Effect
- A moving wave source causes a change in the wavelength.- A source moving towards the observer (your ears) causes the wavelength to be shorter. (velocity)=(frequency)(wavelength) The velocity of the wave does not change so as the wavelength gets shorter the frequency must get higher. ( Pitch of a sound wave is higher. The color of light moves to the blue, higher frequency.)
- A source moving away from the observer (your ears) causes the wavelength to be longer. (velocity)=(frequency)(wavelength) The velocity of the wave does not change so as the wavelength gets larger the frequency must get lower. ( Pitch of a sound wave is lower. The color of light moves to the red, lower frequency.)
VIII. Sonic Boom
- Source moving faster than the speed of the traveling wave.- Wavefronts build up in front of the moving source causing a very large Bow Wave. Contains a large amount of energy.
- Examples: Wave from a boat moving in the water. Jets traveling faster than the speed of sound.
Refer to Conceptual Physics Chapter 18.