1. Chapter 11 Vibrations and waves Goals: Harmonic Motion, Pendulums, wave properties, period, frequency, amplitude, wave speed and interactions of waves

2. How does Energy move? Section 11.1  Forms of Energy – mechanical, thermal, chemical, electromagnetic, electrical and nuclear  Moves by conduction, convection and radiation  In the form of waves  Wave = repeated disturbance in matter or electromagnetic fields

3.  Simple Harmonic Motion – repeated motion with a displacing force and a restoring force  Back and forth motion  ex: springs and pendulums  Pendulums demonstrate simple harmonic motion where the displacing force is the force applied and the restoring force being gravity  at low angles as amplitude or mass is changed the period remains the same  Remember: there is a balance between acceleration due to gravity and inertia

4. How does a Pendulum represent Harmonic Motion?  Max displacement to equilibrium to max displacement to equilibrium to max displacement  one cycle or one wave  Amplitude is the max displacement measured by the angle of the string  Period is the length of time for one cycle T  Frequency is the number of cycles per second Hz kHz MHz

5.  T = 2πΓL/g L = length of string  f = cycles/sec f = 1/T  practice problems B pg 378  Pendulum Lab – varied length of the string and mass of the bob  the Period is not affected by mass or amplitude (not much)  the Period is affected by the length of the string

6. What are the different types of waves? Section 11.3  Remember waves transfer Energy E = A²  Two types of waves include: Mechanical and Electromagnetic  Mechanical waves transfer energy through matter - the medium disturbing matter not moving the medium ex: water waves, sound, seismic and tsunami  Electromagnetic- disturbances in electric and magnetic fields empty space

7.  Mechanical waves can be either transverse or longitudinal, but electromagnetic waves are transverse  Transverse waves disturb matter at right angles to the transfer of energy (water)  have a crest and a trough = 1λ  sine wave and can be shown on wave form  Longitudinal waves disturb matter a series of compressions (crests) and rarefactions (troughs) (sound)  wave velocity v=ΔX/Δt v=λ/T and f=1/T  so v = f · λ practice problems D

8. How do waves interact? Section 11.4  Mechanical waves displace matter and can occupy the same space and time  overlap or superimpose  produce interference patterns  Resultant wave is the sun of the waves in the same space and time  Constructive interference – waves add to produce higher amplitudes  Destructive interference – waves with opposite signs cancel partially or completely

9.  Reflection – when a wave returns from a different medium  Demo: hold slinky fixed at one end open at the other and wave will return upright  with both ends fixed the wave will return inverted  Standing wave – appear stationary and are alternating constructive and destructive interferences at certin frequencies  Nodes (des) Antinodes (con)  Fundamental – one antinode, lowest natural frequency or first harmonic

10.  Lab on harmonics  λ = 2L/ harmonic  ex: third harmonic λ = 2L/3 or 2/3 m

11.  Waves are not only a lot of fun to study  they also bring music to our ears, so  Study for tomorrows Exam  that is some sound advice!!!