Materials: Computer and School Network |
Time Allotment: 4 Class Days |
The purpose of this lab is to investigate some variables which effect the speed of a wave and to use graphical analysis methods to derive and interpret wave speed equations based on collected data.
The Physics Explorer - Waves software models the motion of a wave (or a pulse) along a medium. The medium is depicted as a string of 50 masses (representing the particles of the medium) connected by springs. As a disturbance or pulse is introduced into the medium, it moves from one mass to the next. The masses, being connected to each other by springs, interact with each other in order to transmit the energy of the disturbance along the medium. The properties of the medium (and of the wave) can be set by the user using data input boxes.
In the first part of this activity you will investigate the effect of two media properties (stiffness and mass) upon wave speed.
Sping Constant, k (N/m) |
Distance (m) |
Time (s) |
Speed (m/s) |
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Mass, m (kg) |
Distance (m) |
Time (s) |
Speed (m/s) |
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For each set of data, utilize the Graphical Analysis program (found on all school servers) to determine the quantitative relationship between the variables under study. Construct a plot of speed vs. spring constant (speed is plotted along the vertical axis) and speed vs. mass ( speed is plotted along the vertical axis). Be sure that the Regression Line, Point Protectors, and Statistics options are selected under the Graph menu and that each axis is labeled with a quantity symbol (v, k, and m) and a unit. For each graph, raise the quantity plotted along the horizontal axis to some power in order to obtain a line with the best-fit (refer to the Graphical Analysis manual or relevant Survival Packet pages). Once a best-fit line has been obtained and a COR of 0.996 or less is obtained, print the graphs (with Statistics showing) and submit with your final lab report.
In the table below, write the equations representing the quantitative relationship between the two variables plotted along each graph.
Speed vs. Spring Constant |
Speed vs. Mass |
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Many waves are not just single disturbances, but are continous phenomenon, periodic in both time and space. In the Part B of this activity you will investigate the effect of two wave properties (frequency and wavelength) upon wave speed.
Run the simulation and watch the wave train travel down the string.
How do your results compare to the results in Part A for the same values of mass (1 kg) and spring constant (10 N/m)?
Frequency (Hz) |
Wavelength (m) |
Time (s) |
Distance, D2-D1 (m) |
Speed (m/s) |
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A standing wave is a wave in which there are points along the medium which appear to be standing still and still other points along the medium which undergo a maximum displacement. Standing waves are the result of two waves within the same medium and traveling different directions such that they interfere and produce a wave pattern known as a standing wave. In Part C of this lab, you will investigate the effect of a few variables upon the speed of a standing wave. You will do this by simulating the motion of a guitar string. A string with both ends fixed is brought into the shape of a full sine curve and then left alone to start vibrating.
Check that the "Standing Waves" window shows these values.
Run the simulation and watch the string begin moving.
Change the number of starting wavelengths found between the ends of the medium and repeat the simulation. Mesure the wavelengths in each case and complete the table below. Use the reciprocal of the period to calculate the frequency. Use the frequency and the wavelength to calculate the speed of the wave.
Number
of Wavelengths
Wavelength
(m)
Period
(s)
Frequency
(Hz)
Speed
(m/s)
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What is the relationship between these values? Explain.
Using a well-written paragraph, discuss all the variables which were studied in this lab and identify their effect (if any) upon the wave speed. Do a bang-up job!
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This page created by Tom Henderson and last updated on 8/29/97.