03/19 Tuazon

Turned in:
Doppler Effect Simulation
16.9 and 16.10 Guided Reading

Returned:
Sound Reading Questions

Class activities:
Doppler Effect Notes
Shockwaves Worksheet

Homework:
Shockwaves Worksheet (if not finished in class)
Honors Physics 3rd Quarter Test Review (begin working on this)
P. 507, #70-76 in our textbook
Study for sound test on Monday

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With my Doppler Effect Simulation and Guided Reading already turned in before school started (I had to come in early because my computer would not run the simulation) and my Sound Reading Questions already picked up out of my folder, I went up to the board to write down the honors physics homework really quick. To my side, I could hear Jeff and a few other people complaining about something Mr. Ebersole said, and as I tuned in, I heard great news that we had a sound test on Monday.

Yeah––the first real test we would have in weeks would be on exam week.

I joined in with the petty whining for a while, with Mr. Ebersole telling us to calm down, before returning back to my seat and watching as Mr. Ebersole prepared to show us some equipment to demonstrate the Doppler Effect.

One thing I remember them comparing the two pieces of equipment they used. One was a really expensive metal rod with a tone box attached to the end of it that could probably decapitate Mr. Ebersole if he did not move out of the way, while the other one was a rubber tube that Ms. Grote bought for $1 at a toy store that did not even need the tone box at the end to demonstrate the same thing. Coats-Haan said something about how East is obviously superior because of this.

Anyway, for the demonstration, Mr. Ebersole waved both sounding objects around his head, and the pitch became higher as the source moved closer to us, and the pitch lowered moving away from us. This is because of the source's velocity.

Then we went off to take notes, which Mr. Ebersole was really excited about ("Oh my gosh, we get to skip a ton of slides today! We've just made this powerpoint go from 19 slides to 6 slides!").

We learned that the general form for the Doppler Effect is:

fo = fs (1 ± vo/v) / (1 ∓ vs/v)

The variables for this are:
fo = frequency observed
fs = frequency of source
vo = velocity of observer
vs = velocity of source
v = speed of sound

Note: The upper signs of the + or - sections of the equations are used when the observer or source is going toward the other, and the bottom signs of the + or - sections of the equations are used when the observer or source is going away from the other.

We also did example problem #6 and #7, in which all you have to do is plug in the known values to find the frequency of the source and the frequency observed, respectively. The answer for #6 is 490 Hz, and the answer for #7 is 410 Hz.

Additional note from questions other students asked in class:
- Depending on direction the observer and source are going in relation to each other, you may use both top signs, both bottom signs, or one of each sign in the equation.
- If either the observer or source is stationary, their respective top or bottom portion of the equation will end up being zero.
- As long as the speed of the observer and source stay the same, the frequency observed will be the same, even if one catches up with the other. However, at the point when the observer is on the opposite side of the source, the frequency observed will be different (yet still consistent on that side of the source).

Finally, we wrapped our our period working on a Shockwaves Worksheet.
This is what my table concluded (We also got 100% on our worksheet according to HAC, so this information should be accurate)
- As speed increases, the angle of the spacecraft to the shockwave gets narrower
- The distance of the the spacecraft goes divided by the distance the shockwave goes (its radius) is the relative speed of the spacecraft to the speed of sound.

For example: If the spacecraft moves 8 cm, and the shockwave has a radius of 2 cm, 8 cm divided by 2 cm is 4, meaning the spacecraft is going 4 times the speed of sound.

Wow, that was a lot of information. Feel free to ask for clarification.

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Question of the Day:

Describe a situation where both the signs are positive in the Doppler Effect Equation.
--ch

Answer: A situation in which the observer is going toward the source and the source is going away from the observer would result in both signs being positive in the Doppler Effect Equation. Such a situation may be Trevor moving toward Chris, trying to get him to work on stuff for our Rube Goldberg Machine, while Chris is covering his ears, making a really annoying sound to block out Trevor's requests, and running away.