+

Perceiving Sound

+Before we start! A review of Light

+Light vs. Sound

Light Sound - 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.

+

+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?

+What happens when you age?

http://www.youtube.com/watch?v=qNf9nzvnd1k

http://www.youtube.com/watch?v=VxcbppCX6Rk