1. SOUND An Introduction to Sound Created by Joshua Toebbe NOHS 2015

2. Introduction to Sound We all experience sound everyday, in some way shape or form. Even deaf people who can’t hear normal frequencies can here infrasound waves. So lets take a look at what exactly sound is. Created by Joshua Toebbe NOHS 2015

3. Introduction to Sound Sound is a longitudinal wave. (media movement is parallel o the wave propagation) Lets take a look at a speaker. Created by Joshua Toebbe NOHS 2015

4. Introduction to Sound A speaker has a small cone inside which moves back and forth. Created by Joshua Toebbe NOHS 2015

5. Introduction to Sound When the cone is pushed forward it compresses the air in front of it. Created by Joshua Toebbe NOHS 2015

6. Introduction to Sound When the cone is retracted the air in front of it is expanded. Created by Joshua Toebbe NOHS 2015

7. Introduction to Sound The resulting back and forth motion creates a longitudinal pressure wave in front of the speaker. Created by Joshua Toebbe NOHS 2015

8. Introduction to Sound The compressions correspond to the peaks of the wave, and the expansions or rarefactions correspond to the troughs of the wave. Created by Joshua Toebbe NOHS 2015

9. Introduction to Sound What affects the speed of sound? Medium density Medium temperature (which affects density) Oh yeah, and the density of the medium… Okay so its just density. The frequency of the wave determines the pitch. Since frequency stays constant when changing media, but wavelength and speed change, sounds have a different pitch in different media. Created by Joshua Toebbe NOHS 2015

10. Introduction to Sound Does sound travel faster in denser or less dense media? The speed of sound in air is 340m/s The speed of sound in water is 1497m/s So it seems as though a denser medium has a higher wave speed. Created by Joshua Toebbe NOHS 2015

11. Introduction to Sound Does sound travel faster in denser or less dense media? The more dense the medium, the faster sound travels? This seems counter intuitive So lets think about it. Sound travels as energy is transferred from one particle to another. The closer the particles are, the faster the energy gets transferred. But at the same time, more energy is required to move each particle… Created by Joshua Toebbe NOHS 2015

12. Introduction to Sound Lets see if we can find a way to calculate how the speed will change based on the density. We know the speed of sound in air is 340m/s. We also know the speed of sound in fresh water is 1497m/s. We also know the density of water is 1000 kg/m^3 Created by Joshua Toebbe NOHS 2015

13. Introduction to Sound Created by Joshua Toebbe NOHS 2015

14. Introduction to Sound Wait a minute… what is the difference between air and water I mean other than the obvious liquid gas thing Air is compressible, water is not! This means there is another factor that affects sound speed… Elasticity of the medium. Or the magnitude of the restoring force returning each individual particle to its initial position. Created by Joshua Toebbe NOHS 2015

15. Introduction to Sound So you guessed it… Simulation time. Created by Joshua Toebbe NOHS 2015 http://phet.colorado.edu/en/simulation/wave-on-a-string

16. Introduction to Sound So we clearly see that as tension increases wave speed increase, and it is not a linear relationship. Lets see what happens when we look only at density. Created by Joshua Toebbe NOHS 2015

17. Introduction to Sound Here we are holding elasticity, or restoring force constant. Most gasses have an extremely low elasticity, so if our previous inference was correct, the denser the gas, the faster the sound. But this is not true. In gases with similar elasticity. Denser gases, means slower sound. Created by Joshua Toebbe NOHS 2015

18. Introduction to Sound Created by Joshua Toebbe NOHS 2015

19. Introduction to Sound Created by Joshua Toebbe NOHS 2015

20. Introduction to Sound Created by Joshua Toebbe NOHS 2015

21. Introduction to Sound Created by Joshua Toebbe NOHS 2015