Waves and Sound

1. Waves and Sound Honors Physics Unit 6, Lecture 1

2. Periodic Motion • Periodic Motion is any motion that repeats itself. • The time it takes to complete a cycle is the period • Examples: • Planetary Motion • Fertility Cycle • Pendulum • Mass on a Spring • Ocean Wave

4. A Special Case • Simple Harmonic Motion is a special type of periodic motion. • Example: A mass oscillating on a spring. • Demo here

5. Simple Harmonic Motion

6. What Causes SHM? • A linear restoring force is any force that opposes the displacement of an object from equilibrium with a force that is proportional to the displacement from equilibrium • Linear Restoring Forces result in simple harmonic motion.

8. Hooke’s Law

9. Springs and SHM • Because a spring exerts a linear restoring force on a object, it causes the special case of periodic motion that is called simple harmonic motion

10. Describing SHM • Period • the time it takes for the motion to repeat. • Variable: T • measured in seconds

11. Describing SHM • Amplitude: • the maximum displacement of the system from equilibrium. • Variable: A • measured in meters • Frequency: • the number of cycles that are completed in a second. • Variable: f • measured in cycles/sec (Hertz)

12. Describing SHM

13. Frequency • Frequency is measured in Hertz

14. Example • A mass bouncing on a spring completes 5 cycles in 8 seconds. What is the frequency and period of this motion?

15. Example

16. Other Examples of SHM • Pendulum • Atomic Vibrations • Light • Sound • Electricity (AC)

17. The Pendulum • Gravity provides a linear restoring force

18. Pendulum Example #1 • Find the period of a pendulum that is 2 meters long.

19. Pendulum Example #1

20. Pendulum Example #2 • Find the length of a pendulum if the period must be 1.000 sec • L = 0.248 m

21. Waves • What is a wave? • A wave is a disturbance in a medium. • Energy is transmitted but not matter • What is a medium? What is the media, or media center? • A medium is any material or field that is connected in such a way that a disturbance (energy, information) can pass through it.

22. Types of Waves • Pulse Waves • do not repeat • Periodic Waves • are created by repetitive events

23. Types of Waves • Transverse Waves • The disturbance of the media is perpendicular to the direction of energy propagation • Longitudinal Waves • The disturbance of the media is parallel to the direction of energy propagation • Torsional Waves • The disturbance of the media is a rotation about the axis of energy propagation

24. What wave is this?

25. Wave Examples

26. Wave Examples

27. Wave Examples

28. Water Waves

29. Understanding Waves • Waves are characterized by 4 parameters: • Wavelength • Period • Frequency • Amplitude

30. Relationships

31. Wave Speeds • For Sound, the speed of the wave is about 341 m/s at room temperature • For EM waves, like Light, Radio, Microwaves, X-rays, etc, the speed of the wave is 3.0 x 108 m/s

32. Example • Find the period and the wavelength of a radio wave that has frequency of 90.1 MHz