1. Resonance – Learning Outcomes
Define natural frequency.
Define fundamental frequency.
Define resonance.
Give examples of resonance.
Demonstrate resonance.
Discuss resonance with vocal folds.

2. Natural Frequency
The natural frequency of an object is the frequency at which an object will vibrate at if it is free to do so.
Every object has a natural frequency and will vibrate at it if set to do so.
Many objects vibrate weakly or at frequencies outside the limits of audibility so we cannot hear them.
The fundamental frequency of a body is the lowest frequency is the lowest frequency which is produced by the vibration of an object.
We will look at this in more detail for types of instruments later.

3. Resonance
Resonance is the transfer of energy so that a body vibrates at its natural frequency.
e.g. pushing a swing at the right time in its swing will cause it to move back and forth at its natural frequency.
Pushing incorrectly can reduce the vibration.

4. Examples of Resonance
Some opera singers are able to shatter glass by singing at its natural frequency.
Sound produced by your vocal folds resonates in your larynx, throat, mouth, and nose, producing a much louder sound than the folds make on their own.
Buildings and bridges have been known to resonate with earthquakes, wind, and pedestrians.

5. To Demonstrate Resonance
Set a number of pendulums of varying lengths to hang from the same horizontal string.
Attach one extra “driving” pendulum that has the same length as one other pendulum to one end of the string and set it to swing.
Note that each pendulum will start swinging back and forth, but the one with the same length as the driving pendulum will swing much higher.
These two pendulums have the same natural frequency so they transfer energy between each other easily via resonance.
This is called Barton’s pendulums