PURPOSE: In this experiment the wave velocity will be calculated and compared to the theoretical value.
THEORY: The velocity of a wave on a string is given by
Where F is the tension in the string and m is the linear mass density (m = M/L). The velocity of a wave is also given by
where f is the frequency and l is the wavelength. The wave velocity will be measured and compared to the velocity calculated from theory
EQUIPMENT: Computer and VideoPoint software.
PROCEDURE:
1. Work with the UMD004 video. (A step-by-step procedure for using VideoPoind is given below.)
2. Click on the same point on one of the spring as the wave travels down the spring.
3. Calibrate the video.
4. Record the mass, length, and mass for each of the spring, (There is a mistake on the first screen of this video. The unit for the length should be meters not Newton’s)
5. For each spring determine the distance the waves travel by the finding the difference in the positions and the time of travel by the finding the difference the times for these data points. Use the data for which the wave could bee seen in the video.
6. Calculate the wave velocities by dividing the distances traveled by the elapsed times.
7. Calculate the wave velocities from the tensions and linear mass density.
8. Find the percent error in the wave velocities.
Start VideoPoint.
Click left mouse button while the pointer is anywhere inside the "about VideoPoint" dialogue box.
In the "open" dialogue box do the following.
Select the drive letter of the CD drive in which VideoPoint is located.
Select movies folder and the appropriate folder under movies (here the "UMD" folder).
Under filename select the appropriate file to be loaded (UMD004).
Press "OK".
The "Number of points" dialogue box will appear. Make sure "2" is selected and press "OK". The movie and software should now be loaded.
On the menu bar select "Movie" and "Full Screen" using the left mouse button.
Record data -When the cursor is inside the movie screen it appears as a target. Place this target cursor on the maximum point on the top wave and press the left mouse button, repeat the process for the bottom wave, the movie will advance one frame and the data is recorded. . The maximum for the wave may not be visible in each frame if this is the case place the cursor on the origin to record the data. Repeat this process until all frames of the movie have been used. Be consistent and use the same point on the wave each time to record the data .
Calibrate the movie.
Move the cursor to the "meter stick" tool button at the left of the screen (6th button from top) and click the left mouse button.
The "Scale Movie" dialogue box appears. Select continue with the left mouse button.
Put the target cursor on the left end of the meter stick in the first movie frame and press left mouse button - repeat for the right end of the meter stick.
On the menu bar select "Movie" and "Normal Size".
Transfer the data
With cursor inside table area click left mouse button to select table.
Put mouse in title area of table and click and hold left mouse button
and drag the
table to top of window.
Place the pointer on lower right corner of table (cursor should be double arrow) and drag the corner of the table to make the table larger so all the data can be seem.
Record the time and the X-position for each wave in the provided data table.
QUESTIONS:
1. Every thing else being constant, what must the tension in the string do in order to double the number of segments produced on the string?
2. How much error is being introduced into the calculation of the velocity by the linear mass density changing because the string is stretching?
3. Are the waves on the string longitudinal waves or transverse waves.
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Mass of spring M = __________
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