2. Sound Waves If a tree falls in the forest and no one is around to hear it, does it make a sound?? What is sound?? Disturbance that travels through a medium as a longitudinal wave

3. Making Waves How do sound waves start? From your experiments yesterday how did the sound waves start in the mini labs Starts with a vibration Vibrations move particles nearby As source of sound moves back and forth rarefaction and compression occur

5. Travelling sound Each particle in medium vibrates Gets to your ears – you hear sound Common medium is air Can go through other mediums too!! Wood – knocking on a door Can you thin of others? Write a few down in your notes

6. How they interact! Reflection: Sound reflects (bounces off) certain materials Harder and smoother surface = stronger reflection Echo Clap hands in a gym Diffraction: Sounds waves do not always travel in a straight line Can bend around corners!! Interference: Sound waves can interact with each other!

9. SPEED OF SOUND Why do you usually hear thunder after you see lightning? Sound travels more slowly than light!! Sound waves travel through different medium (what’s a medium?) Speed depends on: Elasticity Density Temperature

10. SPEED OF SOUND Elasticity – ability to bounce back What happens when you stretch a rubber band? What happens when you stretch modeling clay? Elasticity of a medium = how well particles bounce back after being disturbed More elastic = faster sound travels through it Liquids = not elastic = sound travels slowly

11. Speed of Sound Density – amount of matter in given space Denser object = SLOWER SOUND Lead & silver = slow Iron & steel = faster! Temperature Sound travels more slowly at LOWER temperatures At high temp. particles move more slowly = more difficult to move Where would sound travel more slowly? Higher or lower altitude?