1. Periodic Motion • Common Example: Pendulum • Some elements of periodic motion we can describe • Oscillation or Cycle • Period, T • Frequency, f • Amplitude, A • Another Common Example: Mass on a spring

2. Waves Another cycle One cycle

3. Wavelength  Amplitude A Amplitude A Wavelength  Waves Distance traveled by the wave in 1 cycle is the wavelength,l Crest Trough Frequency, f: number of cycles that the wave goes through in a unit time (usually 1 s)

4. Waves/Periodic Motion You are sitting on a dock, and using binoculars, you notice a boat bobbing in the distance. You notice that if you start timing when the boat has bobbed up, at the end of 2 seconds, the boat has bobbed up 6 more times. You also notice that the distance between the wave crests causing the boat to bob up (and down) is 4 m. a. What is the frequency of the waves? b. What is the wavelength? c. What is the period? d. What is the speed of these waves?

5. Classification of Waves Transverse Wave Direction of oscillation is ⊥ to direction of propagation Longitudinal Wave Direction of oscillation is along direction of propagation

6. Sound Waves Compression and Rarefactions

7. Frequency and Sound Waves Frequency of Sound is perceived as pitch Most humans can detect sound with frequency ranging from 20 to 20,000 Hz Below 20 Hz is called infrasonic Above 20000 Hz is called ultrasonic the mosquito

8. Speed of Sound Waves • at 20 oC in air is about 340 m/s

9. Some Important Properties of Waves • Reflection • Doppler Effect • Refraction • Interference

10. Echo Location • At a particular temperature, sound travels in water at about 1530 m/s in water. If a dolphin emits a sonar cry and hears the echo 3s later, how far away from the dolphin is the object from which the signal is reflected?