Resonance and Forced Vibration Or the Walls come tumbling down

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

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

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

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?

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