Journal 4/25/16 How do you think a bell makes sound? Explain in as much detail as you can. Do this warm-up with a friend to see just how much you can figure out. Objective Tonight’s Homework To learn about the Doppler Shift and resonance p 449:3 p 457: WDYL 1

Doppler Shift, Pitch, and Resonance We start getting an odd effect when we have sound waves moving at high speeds. Below, we have a sound wave coming from an object that isn’t moving. You’ll notice that the sound waves spread out evenly on all sides. They all have the same pitch.

Doppler Shift, Pitch, and Resonance In this example, the source of our sound is now moving to the right. If you look closely, you’ll notice that the waves on the right side are closer together than the ones to the left. The ones to the right will have a higher pitch than the non-moving waves and the ones to the left will have a lower pitch than the non-moving ones. This is what we call the Doppler Effect.

Doppler Shift, Pitch, and Resonance If an object goes past you at high speed while making sound, you’ll notice this effect. The sound will start out at a higher pitch, then as it passes you, the sound will suddenly drop lower in pitch. You most often see this with fire trucks, police cars, ambulances, and trains.

Doppler Shift, Pitch, and Resonance Resonance is a special effect where one object will vibrate from the sound waves coming from another object. Most objects will only resonate at certain frequencies. Think of this like a person being pushed on a swing. If the person times their kicks just right, the swing will go higher and higher with only a little effort. If you kick at the wrong time, you just end up stopping.

Doppler Shift, Pitch, and Resonance This same phenomenon exists with pretty much everything. If you tune a musical instrument right, the correct tuning fork will vibrate in resonance with the right note. Loud bass at a concert will cause your chest to resonate at the right frequency. Rocking in a rocking chair requires very little energy because you know how to make the chair resonate. The military has even looked into “sonic” weapons that could resonate an enemy’s head hard enough to make it explode!

Measuring Decibels We have a lab on Thursday. With this lab, Mr. C. is going to generate some sound. Your job will be to build a device that can detect and measure that sound. Your hint is to think about what loud, low bass sounds do.

Exit Question Which of the below is an example of resonance? The sound of a bell continuing for several seconds after it has been rung A A speaker making a buzzing noise when the right note is being played A All of the above None of the above