Block waves

Wed/Thurs physics block.
Yeah double physics!!!

We did lots of things in this class.

First, we finished the second slinky lab.
Then we talked about the lab: standing waves, medium determines the speed, etc.

We discussed the terms "node" and "anti-node" and saw the visual of the bugel playing, with a representation of the nodes/anti-nodes (click the "physics" button on the bottom to display)

We saw the video clip of "slinky football", showing different slinky/spring waves traveling across a surface. The interesting part was when one slinky was stretched out, and one was looser, the wave traveled faster in the tight one. Then we looked at three different materials (garden hose, slinky, and brass spring). We saw that each material, stretched that distance, had a different speed.

Next, we looked at water waves in the ripple tank, and examined a "moire" pattern on a small handout (circles on paper and transparency sheet, overlapping).
A few simulations showing this:
http://www.walter-fendt.de/ph11e/interference.htm

http://www.falstad.com/ripple/ (adjust the simulation to "2 sources, 1 frequency")

We listened to this same phenomenon happening with sound waves, pumping an annoying tone through the classroom, out of two speakers. The waves interfered with each other, sometimes making a loud sound, sometimes cancelling out.

We then worked on a homework assignment, drawing wave superposition witih triangle and square waves.
See more wave superposition: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=35
and even more: http://www.kettering.edu/~drussell/Demos/superposition/superposition.html

Last, I handed out a homework assignment and talked about the first few problems (car suspension and blinker synchronization). This homework will probably be taken up on Monday.

wave superposition homework should be done-ish by Friday. If you have questions, we can address those and I'll take the work on Monday.

Friday we'll look at standing waves on a string, and more sound/instrument related phenomena.

the medium determines the speed

This is the "moral" of the activities that we are doing.
We are examining the relationship between velocity, frequency, and wavlength.
The speed does not depend on the frequency.
The speed does not depend on the wavelength.
The speed only depends on the material.
So if you change the material (different spring, different tension) the speed will change.
If you increase the frequency (shake your hand faster) it does NOT change the speed.
What it DOES do, is decrease the wavelength.

Class today was a little disombobulated because of the modified schedule for class meetings.
Hope you enjoyed them. During class we worked on finishing up the lab, and talked a little about "nodes" and "anti-nodes".



Wed/Thurs during block we'll work more on wave interactions. Interference and standing waves. We'll look at water waves, listen to sound waves, and see some computer generated waves.


Here's another great website that shows lots of the stuff we've been working on:
http://id.mind.net/~zona/mstm/physics/waves/waves.html

slinky - part two

Today we worked through some of the math problems and talked about the homework.
Some students had me examine their paper, then they'll finish it at home and turn it in tomorrow.
We started another slinky lab today. We'll finish it on Tuesday.
The purpose of the lab is to examine more of the relationships and behavior of waves.
First, vel = freq x wavelength
Second, the effect of the material on the wave speed, freq, wavelength
Third, the pattern of a "standing wave", when a wave travels down the spring, bounces off the end, comes back, and collides with the waves that are traveling down the spring. The standing wave pattern has "nodes" and "anti-nodes" . A full wavelength, includes two "humps".

Take a look at this tutorial stuff, if you would like more words, etc.
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/waves/u10l4c.html

here's another site with good graphics, but it gets a little more complicated than what we're doing: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/standw.html

no new homework today, but some people are finishing their previous one. We'll finish the lab tomorrow, and maybe get one more assignment (with time in class to work).

more waves AND homework help

Friday... We plowed through the key definitions, looked at some video clips (I'm putting them onto the website soon, so look online if you are interested in seeing them again).

The homework is due Monday. We didn't have time to work through numerical examples, but do your best.
Here's a few answers that might help:

2d) one wave every two seconds, means 1 wave/2 sec = 0.5 waves/sec
2e) use the frequency of the above problem (f=0.5 Hz), use the given speed v= 3 m/s. Use the equation velocity= frequency x wavelength --> so wavelength = velocity/frequency = 3 m/s / 0.5 waves/sec = 6 meters/wave.
Notice that the UNITS are all in there.


4d) Radio waves travel at the speed of light. v=3 x 10^8 m/s. The frequency is 85.5 MHz, which is 8.55 x 10^7 Hz (85.5 x 10^6 Hz). So, velocity= frequency x wavelength --> so wavelength = velocity/frequency = (3 x 10^8 m/s )/ (8.55 x 10^7 cycles/sec) = 3.5 m/cycle
So the wavelength is 3.5 meters long.

5c) this is kinda a trick question. the velocity is determined by the medium, not the frequency.

waves stuff

Today we tested our theories on the speed of a slinky wave.
We had lots of good experiments, some of them found no appreciable difference between their variable and the wave speed. For example, the size of the wave pulse, or the frequency of the pulse did not affect the speed.
But the one factor that did, was to change the medium. In other words, the material.
In this case, we are talking about the slinky. Stretching the slinky more/less caused the wave speed to change. This is a general property of waves.
We discussed the example of sound waves traveling through different air (hot/cold or nitrogen vs. helium). We also talked about water waves, and how the speed slowed as the water got shallower and they "crashed" on the shore.
We discussed some of the major wave terminology: Amplitude, wavelength, frequency, period, and of course wave speed (or velocity).
You can find some nice tutorial stuff here:
http://www.physicsclassroom.com/Class/waves/wavestoc.html

There was homework handed out today.
It is due on Monday.
Come with questions on Friday, where we'll talk more about wave terminology and a few equations, and see a few other slinky things.

Intro to waves

Today we talked briefly about data collection (stopwatch activity)
Then worked on the first few parts of the slinky lab.

Everybody did a great job NOT screwing up the slinkies. Let's hope that the other 6 classes do as well as you did! (We'll find out tomorrow when we pull the slinkies out again!)

Homework for tonight is to prepare your experiment for tomorrow. Devise a method to test the effects of on the speed of a slinky wave.

First day of class

Well, first day has come and gone.
Looks like it will be a fun year!
Here's what we did:
1) syllabus and discussion about course policies and guidelines.
2) short survey (hand in)
3) name physics-stuff, and get-to-know you activity.
4) a few demos

Come back for more!
Remember, if you have any questions/concerns/ please let me know.
you can stop by class, or send me an e-mail. schuetz.physics@gmail.com

Welcome to class!!!