How are waves produced? Waves are produced by a wave pulse (a force). A wave pulse is a single disturbance that travels through a medium (water, air, glass, etc..) A traveling wave is a series of wave pulses at regular intervals.
What is a vibration? Vibration: the motion of an object that regularly repeats itself, back and forth, over the same path. Other words for vibration: oscillation, cycle Periodic Motion: when an object moves in a repeated pattern over regular time intervals.
Wave Terminology (Transverse Waves)
Key Terms for Waves Frequency - the number of complete waves produced per second. Symbol = f Units = Hertz (Hz)1 Hz = 1/s (Named after Henry Hertz who discovered radio waves) Formula: where N is number of cycles, t is time Formula where T is the period
Key Terms for Waves Period - time taken to produce one complete wave. Symbol = T Units = seconds (s) Formula:
Example 1
Answer
Check Your Understanding A mass suspended from the end of a spring vibrates up and down 24 times in 36 seconds. A) What is the frequency of the vibration? B) What is the period of the vibration? Use your formula sheet to find!
Answer A) F = N/t F = 24/36 = 0.67 Hz B) T = t/N T = 36/24 = 1.5s
Check Your Understanding A pendulum is observed to complete 23 full cycles in 58 seconds. Determine the period and the frequency of the pendulum.
Answer frequency = 23 cycles/58 seconds = Hz = ~0.40 Hz period = 58 seconds/23 cycles = sec = ~2.5 s
Key Terms for Waves Wavelength - the shortest distance between two repeated points in a wave. Think of a wavelength as the distance between two “humps”. Symbol = λ (lamda) Unit = metre (m)
Key Terms for Waves Amplitude - the greatest displacement of the wave away from its undisturbed position. Think of the amplitude as the height of a hump. Symbol: a
Key Terms for Waves Rest Position: When a pendulum or a mass on a spring is not in motion but is allowed to hang freely, the position it assumes is called its rest position. (also called equilibrium position from Hooke’s Law) Trough: lowest point on a wave (local min) Crest: highest point on a wave (local max)
Questions for you! Consider the diagram below in order to answer questions # The wavelength of the wave in the diagram above is given by letter ______. 2. The amplitude of the wave in the diagram above is given by letter _____.
1. A 2. D
3. Indicate the interval that represents one full wavelength. a. A to C b. B to D c. A to G d. C to G
3. D
Example 2 A mass is tied to a spring and begins vibrating periodically. The distance between its highest and its lowest position is 38 cm. What is the amplitude of the vibrations?
Answer Answer: 19 cm
Example 3: The period of the sound wave produced by a 440 Hertz tuning fork is ___________. Answer: seconds GIVEN: f = 440 Hz Find T T = 1 / f = 1 / (440 HZ) = s
Questions… Page 341, questions 1 to 4