1. + Perceiving Sound

2. + Before we start! A review of Light

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

4. + 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.

5. + Make Observations

6. + Why did this happen?

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

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

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

10. + 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.

11. +

12. + 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.

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

14. + Try some Questions P. 118 # 8- 10

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

16. + 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)

17. + Can we hear all frequencies?

18. + What happens when you age? http://www.youtube.com/watch?v=qNf9nzvnd1k http://www.youtube.com/watch?v=VxcbppCX6Rk