1. Resonance and Forced Vibration
Or the Walls come tumbling down

2. Natural Frequency All rigid objects vibrate including
Solid constructions
Molecular and ionic bonds
Electrons between electron shells
Frequency at which vibration causes the greatest amplitude is called the natural frequency.
Objects can have multiple natural frequencies

3. Forced Vibration
Occurs when object is vibrated at frequency other than natural frequency of object
Must be physical contact between objects for transfer of vibration to occur
Examples:
Tuning fork on table
Music box
Speaker box

4. Resonance Vibration of object at its natural frequency.
Vibration can be transferred w/o physical contact.
Resonance can occur with frequencies lower than the natural frequency of the object but not above
Examples: Bridge breaking, shaking of glass shelves, car vibrating, sympathetic strings of sitar, swing, Breaking a glass with voice, tuning radio stations

5. Check Question: The Three Tuning Fork problem
Three tuning forks of frequency 20 hz, 40 hz and 80 hz are placed near one another. Which forks will vibrate in resonance when the following fork is struck: a) 20 hz b) 40 hz c) 80 hz?

6. Calculating Resonance for Standing waves along strings and pipes
For string connected at both ends or pipe open at both ends
Frequency=2v/ nl where n = 1,2,3…
Length of string =nl/2
For closed pipe
Frequency = 4v/nl where n= 1,3,5, …
Length of pipe = nl/4
N=1 is called the fundamental frequency or first harmonic and is lowest frequency heard