Quiz next week and practice HW

On the quiz:

1.  Energy:  Potential (mgh) and kinetic (0.5 mv^2).  How to calculate these and use the conservation of energy principle.

2.  Period of pendulum formula use

3.  Parts and properties of a wave

Quiz dates:

A:  2/15
E:  2/16

A draft of the lab will be due the class AFTER the quiz.

Practice problems:

Consider a 5-m long pendulum:

1.  What is the period of this pendulum?
2.  What is the frequency of oscillation of this pendulum?
3.  Where in its swing does it have maximum PE?
4.  Where does it have maximum KE?
5.  Where are the PE and KE equal?
6.  Where is the speed greatest?

Imagine that this pendulum has a 4-kg ball and it is lifted to a point 2-m above the lowest point in the swing.

7.  How much PE does it have at this location?
8.  How much KE will it have at the lowest point in the swing?
9.  What will the speed be at the lowest point in the swing?

Wave question

10.  Consider a string that is 0.5-m long.  If its n=3 harmonic has a frequency of 15 Hz, what is the wavelength and speed of this wave?

Things to include in your lab report

1.  Title - you make up one

2.  Your name and name(s) of lab partners

3.  Date(s) performed

4.  Purpose(s) of experiment

5.  Data table, including headings and units

6.  Analysis where you try to answer these questions:

- How is frequency (f) related to harmonic number (n)?
- How is speed (v) related to harmonic number (n)?
- How is speed (v) related to tension (provided by weight, W)?

Anything else that you noticed in the experiment?  How is frequency related to tension?  This may remind you about certain musical instruments, etc.  Write about anything that is interesting and related.

This is where the bulk of the writing in the write-up occurs.

7.  Sources of error (threats to validity)

8.  General concluding remarks

A and E block lab prep

During our next class, you will collect data for the new "harmonics on a string" lab.  Here is what to expect:

Procedure:

1.  Assemble harmonics apparatus:  sine wave generator, oscillator, string, pulley, weight to hang over end.

2.  Record L, the distance from oscillator (metal tip that vibrates) to top of pulley.  Keep this fixed during the experiment.

3.  Starting from a frequency of 1 Hz, raise the sine wave generator until a clear n=1 harmonic is formed.  You may find that the frequency is not an integer number.  Record the frequency for the clearest harmonic you and your partner(s) can find.  Repeat this for the next several harmonics, as many as you can see.  Use a strobe light if helpful.

4.  In a table, record the following (though not necessarily in this order):  m (kg), W (N), L (m), n, f (Hz), wavelength (m), and v (m/s).

5.  Calculate the relevant weights, wavelengths, and speeds for all trials.

6.  Try a different hanging mass and repeat the experiment.  If you have time, do additional hanging masses.

Analysis

You have data and calculations.  What can you see (and say) about these relationships?  You'll need to write about each relationship, and supply a graph (if helpful to make your case).

- harmonic number and frequency
- speed and frequency
- speed and tension (supplied by the hanging weight)*

* You may need to obtain data from other groups, particularly if you are generating a graph here.

What things can you conclude about waves on a string?  Are these ideas applicable to sound waves in air?

This lab write-up will be due in 3-4 classes after you perform the experiment.

E block physics today

Hey gang,

I'm not in school today.  Here's what you should work on:

1.  Review the HW problems with your table.

2.  Come up with definitions (and drawings, where relevant) for:

- crest and trough

- wavelength

- amplitude 

- frequency

- wave speed

Thanks.

A and E block HW

1.  Calculate the period of a 2-m long pendulum.

2.  How would the period of this pendulum be affected by relocating it to the Moon?

3.  How long should a pendulum be if it is to have a 1 second period?

4.  What exactly is a "wave"?  Try to come up with some type of definition.

A and E block HW

1.  Make a graph of T (time for one oscillation, in seconds) vs. length (in m).  T is on the y-axis.  What type of mathematical relationship seems to represent the data?

2.  Look up an equation for "period of simple pendulum".  What type of curve does this equation suggest?  Does your data seem to represent this?

3.  How could you tell how "good" your data is?  How can you test it in relation to the equation above?  Try it, if possible.

A and E block HW for Thursday (to be collected)

1.  What is the location, relative to the center of the Sun, of the CG of the Sun-Jupiter system?   You may look up needed data to perform this calculation.  Comment on whether or not this CG lies within the Sun itself.

2.  Consider a meter stick (fulcrum located at the 30 cm mark) that is balanced.  The mass of the meter stick is centrally located and is 75 g.  What is the smallest mass that will balance the stick?

3.  Write out your own definition for “energy.”

BONUS:

Consider a 10-feet long 100-lb beam supported on each by cables.  If a 150-lb person is sitting on the beam, 3.5-feet from the left end, what is the tension in each cable?  Believe it or not, this can be treated like a (slightly complex) lever problem.