1. Journal 4/21/16 What kind of music helps you worship God? Is it the same as the kind of music you listen to most of the time? Objective Tonight’s Homework To learn how sound waves work p 443: 3 p 456: 1, 7, 8

2. Sound Waves What is sound? Sound is a wave. It’s air molecules being compressed and expanded. Much like a slinky being pushed with a pulse. Sound waves can also move through water, stone, pretty much anything. We say that the material a sound wave is going through is its medium.

3. Sound Waves We can label a few parts of sound waves. The areas of compression are where air molecules have been squished together. Areas of rarefaction are where air molecules have been stretched apart. The exact way that this looks is what determines what kind of sound we make.

4. Sound Waves So how fast do sound waves travel? Through air, sound travels at about 330 meters / second (1080 ft / second). That’s pretty fast, but still slow enough for the human ear to be able to tell. Any time you hear an echo, you’re hearing sound waves that have hit something far away and bounced back to where you are. Sound is slow enough that you can often tell the difference between the original sound and the echo (reflection) that has bounced back.

5. Sound Waves Light, on the other hand, moves at 300,000,000 meters / second. A million times faster than sound! So when you see light, you really are pretty much seeing it the instant it leaves the source. Using this, you can actually find out how far a bolt of lightning is by the difference between when you see it, and when you hear it.

6. Sound Waves Example: You see a bolt of lightning. 5 Seconds later, you hear the thunder. How far away is the lightning?

7. Sound Waves Example: You see a bolt of lightning. 5 Seconds later, you hear the thunder. How far away is the lightning? velocity = distance / time So… distance = velocity x time distance = (330 m/s) x (5 s) distance = 1650 m (5,413 ft) So this means that for every 5 seconds between lightning and thunder, our lightning is about a mile farther

8. Sound Waves But not all sounds are the same. So what makes one sound different from another? There are a few terms we need to know to explain the differences. The first is pitch. With other types of waves, we call this frequency. This is a measurement of how short the waves are.

9. Sound Waves The wave on the left has a low pitch or long wavelength. The one on the right has a high pitch or short wavelength. The left makes a low note, the right makes a high note.

10. Sound Waves Note that even though some of the waves we just saw were long and others were short, they both still travel at 330 m/s. Pitch is just how close or how far apart they are. The next concept is volume or amplitude. This is how loud the sound is. In our wave, this is how strongly squished or stretched out our wave becomes. the difference between compression and rarefaction.

11. Sound Waves The denser we get the compression and the more thin we get the rarefaction, the louder the sound will be. We measure sound volume with a unit called the decibel. The decibel is a logarithmic scale. What this means is that every time you go up 10 on the scale, a sound is 10 times louder than the one before it. So 40 decibels is 10 times louder than 30 decibels. And 50 decibels is 10 times louder than 40 decibels and so on.

12. Sound Waves

13. As a last point, what makes one thing sound different from another? Most of the things we hear in life aren’t made from just one wave, but lots of waves all put together. This makes most sounds have a very complex pattern of compression and rarefaction. Each specific pattern makes a totally different kind of sound.

14. Exit Question Increasing the pitch of a sound wave will change… How loud it is How high it sounds What type of sound it is How many decibels it has All of the above None of the above

15. Mythbusters Let’s watch one about sound waves!