June 1, 2010 How is sound made? (Do not say instruments… think more in terms of the SCIENCE of sound!) 2. Is there sound in space? Why or why not?
Goals To identify parts of waves To calculate values associated with waves To distinguish between types of waves
Q: What is a wave? Disturbance (vibration) that travels through a medium (substance)
Q: What is a wave? When a wave isn’t traveling, it is considered to be in equilibrium position Imagine a stretched out slinky just sitting on a desk- that’s equilibrium
Q: What is a wave? Once a particle moves at the front, the energy of that particle will travel throughout the slinky to the other end. That creates a wave!
Q: What is a wave? Waves transfer energy, not particles This explains why boats sitting in the middle of the ocean can just sit in one spot, and don’t travel with waves
Q: What are some types of waves? Transverse Particles move perpendicular to the direction of energy transfer Particles move up and down, but energy is transferred left to right. These are the waves we draw/imagine when we hear the word.
Q: What are some types of waves? Longitudinal Particles move parallel to the direction of energy transfer Particles move left and right, energy transferred left and right.
Q: What are some types of waves? Electromagnetic Waves Can transfer energy in a vacuum (SPACE!) Ex: Light waves Mechanical Waves Cannot transfer energy in a vacuum Ex: sound
Q: What are some parts of waves? Transverse Crest (High point) Trough (Low point)
Q: What are some parts of waves? Longitudinal Compression (High pressure) Rarefaction (Low pressure)
Q: What are some parts of waves? Wavelength: length of one cycle Transverse: 1 trough and 1 crest Longitudinal: 1 compression and 1 rarefaction Ex. Distance from one crest to the next Distance from one trough to the next Distance from one compression to the next
Q: What are some parts of waves? Units: same as those for DISTANCE Meters Usually with a prefix NANO 1 m = 109 nm
Q: What are some parts of waves? Amplitude Displacement (movement) of particles from equilibrium (rest) position Most of the time considered to be from rest to crest or rest to trough Harder to measure in longitudinal waves
Q: What are some parts of waves? Amplitude, cont Units: Same as DISTANCE (some form of meters, usually with prefix- see wavelength section) Increased amplitude means louder/more intense sound.
Q: What do you mean when you talk about the frequency and period of a wave? Amount of wave cycles that pass in a certain amount of time NOT the same as speed of a wave! f = cycles time
Q: What do you mean when you talk about the frequency and period of a wave? Frequency, cont Units: Hertz, Hz (cycles per second) Increased frequency means higher “pitch”
Q: What do you mean when you talk about the frequency and period of a wave? The amount of time it takes for one complete cycle (wavelength) Units: same as for time (seconds, hours, minutes, years, etc)
Relationship between the two Q: What do you mean when you talk about the frequency and period of a wave? Relationship between the two As you increase the frequency, the period will decrease Inversely related
Q: What do you mean when you talk about the frequency and period of a wave? Equation: Units: Frequency is hertz (Hz) Period in seconds
PRACTICE PROBLEMS Frieda the fly flaps its wings back and forth 121 times each second. The period of the wing flapping is ____.
PRACTICE PROBLEMS 2. The period of the sound wave produced by a 440 Hertz tuning fork is _________.
PRACTICE PROBLEMS 3. A tennis coach paces back and forth along the sideline 10 times in 2 minutes. The frequency of her pacing is ______.
PRACTICE PROBLEMS 4. Olive Udadi accompanies her father to the park for an afternoon of fun. While there, she hops on the swing and begins a motion characterized by a complete back-and-forth cycle every 2 sec. The frequency of swing is _____. The period of swing is ______.