lab report homework

Lab draft (whatever you have) is due Thursday.  The formal lab will be due TWO classes after that - I think that puts it right after the "In-Mind" days.

Follow the lab guidelines from the earlier post.

Your conclusion should focus on these things:

- What trends can be seen?

- What mathematical relationship(s) can be seen?

- What specific errors are present?

- What can you conclude from the lab?

- Does this have practical applications in real life, and/or is this related to something you've seen before?

Formal lab guidelines - read these and begin to prep your lab

Formal lab guidelines

A draft lab will be due in TWO classes (Thursday), though drafts are generally optional.  The final formal lab will be due in THREE classes (next Monday).

Lab format. 

Typically, each lab should have the following items:

Title  (made up by you)
Your name
Lab partner name(s)
Date performed

Purpose of experiment - a line or two telling me the purpose of your work

Hypothesis (when asked for) - what do you anticipate will be true?

Introductory remarks - "In this experiment, we blah blah blah...." These can be short - it's the place where you say anything special about your approach to the problem.

Data tables - don't forget units

SAMPLE calculation, including relevant formulas used

Graphs, where relevant - there may be no relevant graphs for the wave lab. That part is up to you. Don't forget the units and axis labels.

Conclusion - To me, this is the meat of the lab report. Here are questions to consider:

Discuss the extent to which your hypothesis was validated (or rejected).
Discuss sources of error - be specific. Saying "human error" is somewhat meaningless.
Give suggestions for improvement.
Tell me something you learned and/or liked about the experiment.

The conclusion may be a few paragraphs or a couple of pages (or more, if you write a lot). Be specific, write well, use good grammar and spelling, etc.

In every case, you will be encouraged (but not required) to submit a draft lab. I will get it back to you the same day (in your mailbox) with some comments. The formal lab is typically due the class after that.

Points are deducted for late labs, unless there are extenuating circumstances.

Lab preparation

During our next class, we will investigate the phenomenon of waves on a string - specifically, harmonics on a string.

You will be using the apparatus demonstrated in class.  It generates electronic sine waves which are sent to a vibrating device - the device vibrates at the frequency specified on the sine wave generator.

Your goal will be to determine how the frequency, wavelength, harmonic number (number of half-waves or "humps"), speed and (possibly) string tension (as determined by the weight on the string).

Here are things to think about prior to the lab:

1.  How does the frequency (or pitch) depend on the tension in the string?
2.  How can we generate "harmonics" on a string?
3.  Looking at a standing wave, how could we determine the wavelength of the wave on that string?
4.  What type of mathematical relationship(s) might exist between the variables above?
5.  Look at some applets that demonstrate standing waves or harmonics on a string.  I will post some shortly.

homework

Questions to prepare for next class:

What is the current SI standard of the kg based on?

What is wave interference?

What are "standing waves"?   Are they related to "harmonics"?

Several days ago, you played with an applet designed to show you something about waves.  You may wish to revisit it, if that is helpful, to make your own standing waves.

SI units/standards

Mass is measured based on a kilogram (kg) standard.
Length (or displacement or position) is based on a meter (m) standard.
Time is based on a second (s) standard.

How do we get these standards?

Length - meter (m)

- originally 1 ten-millionth the distance from north pole (of Earth) to equator
- then a distance between two fine lines engraved on a platinum-iridium bar
- (1960): 1,650,763.73 wavelengths of a particular orange-red light emitted by atoms of Kr-86 in a gas discharge tube
- (1983, current standard): the length of path traveled by light during a time interval of 1/299,792,458 seconds

That is, the speed of light is 299,792,458 m/s. This is the fastest speed that exists. Why this is is quite a subtle thing. Short answer: the only things that can travel that fast aren't "things" at all, but rather massless electromagnetic radiation. Low-mass things (particles) can travel in excess of 99% the speed of light.

Long answer: See relativity.

Time - second (s)

- Originally, the time for a pendulum (1-m long) to swing from one side of path to other
- Later, a fraction of mean solar day
- (1967): the time taken by 9,192,631,770 vibrations of a specific wavelength of light emitted by a cesium-133 atom

Mass - kilogram (kg)

- originally based on the mass of a cubic decimeter of water
- standard of mass is now the platinum-iridium cylinder kept at the International Bureau of Weights and Measures near Paris
- secondary standards are based on this
- 1 u (atomic mass unit, or AMU) = 1.6605402 x 10^-27 kg
- so, the Carbon-12 atom is 12 u in mass

Volume - liter (l)

- volume occupied by a mass of 1 kg of pure water at certain conditions
- 1.000028 decimeters cubed
- ml is approximately 1 cc

Temperature - kelvin (K)

- 1/273.16 of the thermodynamic temperature of the triple point of water (1 K = 1 degree C)
- degrees C + 273.15
- 0 K = absolute zero

For further reading:

http://en.wikipedia.org/wiki/SI_units

http://en.wikipedia.org/wiki/Metric_system#History

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In addition, we spoke about the spherocity of the Earth and how we know its size. I've written about this previously. Please see the blog entries below:

http://howdoweknowthat.blogspot.com/2009/07/how-do-we-know-that-earth-is-spherical.html

http://howdoweknowthat.blogspot.com/2009/07/so-how-big-is-earth.html

Fun, and don't forget about quiz next class.

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

http://www.youtube.com/watch?v=0fKBhvDjuy0

http://www.atlasoftheuniverse.com/

http://sunshine.chpc.utah.edu/labs/cosmic_zoom/cosmic_zoom2.swf

http://physics.weber.edu/schroeder/software/zoomer.html

http://htwins.net/scale2/
WAY COOL

Again, worth seeing:

http://www.essex1.com/people/speer/model.html

http://rense.com/general72/size.htm

Also....

Plan on a quiz to take place during the class after next - that would be next Monday.