2. Dr. Joseph W. Howard ©Summer 2006 Periodic Motion

3. Dr. Joseph W. Howard ©Summer 2006 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 Periodic Motion

4. Dr. Joseph W. Howard ©Summer 2006 Waves Wavelength Wavelength Crest Trough Distance traveled by the wave in 1 cycle is the wavelength, Amplitude A Amplitude A Frequency, f : number of cycles that the wave goes through in a unit time (usually 1 s)

5. Dr. Joseph W. Howard ©Summer 2006 Wave Speed Wave speed = (wavelength)  (frequency) Examples: Speed of Sound Waves: 760 mph or 343 m/s Speed of Light Waves: 186,000 miles per second or 300,000,000 m/s

6. Dr. Joseph W. Howard ©Summer 2006 Example A sound wave travels at 343 m/s in an air temperature of about 70 o F. A bottle rocket explodes 0.5 miles away. How long after the explosion do you hear it? 0.5 miles (1600m /1mi) = 800 m d = vt t = d/v= (800 m) / (343 m/s) = 2.3 seconds

7. Dr. Joseph W. Howard ©Summer 2006 Example I count 20 waves hitting shore in 10 seconds. I am also able to determine that the wave peaks are about 2.5 meters apart. What is the frequency of the waves? What is the speed of the waves? Frequency = (# oscillations) / time= (20 waves) / (10 sec) Frequency = 2 Hz Wave Speed = (wavelength)(freq)= (2.5 m)(2 Hz) Wave Speed = 5 m/s

8. Dr. Joseph W. Howard ©Summer 2006 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?

9. Dr. Joseph W. Howard ©Summer 2006 Classification of Waves Transverse Wave Longitudinal Wave Direction of oscillation is ⊥ to direction of propagation Direction of oscillation is along direction of propagation

10. Dr. Joseph W. Howard ©Summer 2006 Classification of Waves Transverse Wave Longitudinal Wave Direction of oscillation is ⊥ to direction of propagation Direction of oscillation is along direction of propagation Animation courtesy of Dr. Dan Russell, Kettering University

11. Dr. Joseph W. Howard ©Summer 2006 Sound Waves Compression and Rarefactions

12. Dr. Joseph W. Howard ©Summer 2006 Frequency & 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 20,000 Hz is called ultrasonic

13. Dr. Joseph W. Howard ©Summer 2006 Some Important Properties of Waves Reflection Refraction Doppler Effect Interference

14. Dr. Joseph W. Howard ©Summer 2006 Some Important Properties of Waves Reflection – bouncing waves

15. Dr. Joseph W. Howard ©Summer 2006 Some Important Properties of Waves Refraction – bending waves Cool Air Warm Air

16. Dr. Joseph W. Howard ©Summer 2006 Some Important Properties of Waves Refraction – bending waves Warm Air Cool Air

17. Dr. Joseph W. Howard ©Summer 2006 Some Important Properties of Waves Doppler Effect – moving wave source Stationary Sound Source Moving Sound Source Faster Moving Sound Source

18. Dr. Joseph W. Howard ©Summer 2006 Interference – Combining Waves Cancelling = Destructive Interference Adding = Constructive Interference

19. Dr. Joseph W. Howard ©Summer 2006 Interference – Combining Waves

20. Dr. Joseph W. Howard ©Summer 2006 Standing Waves

21. Dr. Joseph W. Howard ©Summer 2006 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 2s later, how far away from the dolphin is the object from which the signal is reflected?