# + Perceiving Sound. + Before we start! A review of Light.

## Presentation on theme: "+ Perceiving Sound. + Before we start! A review of Light."— Presentation transcript:

+ Perceiving Sound

+ Before we start! A review of Light

+ Light vs. Sound LightSound - Transverse waves-Longitudinal waves Electromagnetic waves - mechanical waves: require a medium to travel.

+ What do you think is going to happen? Make a prediction. What will happen when air is removed from the bell jar? Don’t forget to explain why.

+ Make Observations

+ Why did this happen?

+ Sound is… A mechanical wave. Longitudinal wave. Produced by the vibration of an object and transmitted to the object’s environment. Requires a medium.

+ The speed of Sound It changes from one medium to another.

+ Why is that? Using the particle model to justify your answer. Why does sound travel faster in solids than in gases?

+ The Decibel (Db) The unit of measurement for the intensity of sound. High Intensity sound = High amplitude = More Decibels. Low Intensity sound = Low amplitude = Low Decibels.

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+ The Decibel Scale All decibel measurements are not completely accurate, they are related to our perception by the human ear. A sound measuring 0 Db is can barely be heard by the ear. We measure variations on the scale by a factor of 10.

+ A Sample of a Decibel Scale Another one can be found on p. 103 of your textbook.

+ Try some Questions P. 118 # 8- 10

+ Pitch and Frequency Lower Pitch = lower frequency sound. High Pitch = Higher frequency sound.

+ Infrasound and Ultrasounds Infrasounds = sounds under 20Hz Used by some animals to communicate. E.g. Elephants Ultrasounds = sounds above 20 000 Hz Used in medical imaging Used by some animals like bats (echolocation)

+ Can we hear all frequencies?