Mechanical Waves Lab: What are the properties of mechanical waves? Central Challenge In this investigation, students use video analysis or other approaches to investigate the properties of mechanical waves using standing wave patterns on coiled springs and strings to determine the relationships among the following properties: frequency, wavelength, and speed. *You may need a partner for this investigation. Objectives After completing this investigation, you should be able to: Describe factors that affect the speed of wave propagation; Define and describe, using correct terminology, the general characteristics of mechanical waves; Background Mechanical waves are disturbances in a medium that transfer energy and momentum from one point to another without actually transferring the molecules of the medium. Longitudinal waves, such as sound waves or compressions of a spring, transfer energy and momentum through solids, liquids, and gases through oscillations of the medium that are parallel and antiparallel to the direction of propagation of energy and momentum. Transverse waves are produced by oscillations such that the motion of the medium is perpendicular to the direction of propagation within the medium. Waves produced by shaking a rope are examples of transverse waves. The speed of propagation (v) of a mechanical wave depends on properties of the medium, such as elasticity and density, and for periodic waves (the focus of this activity), speed is equal to wavelength times frequency (v = /). Wavelength ( ) is the distance along the wave between two successive positions that are in the same phase (e-g., from the crest of one wave to the crest of the next wave). Frequency (f) is the number of complete oscillations per second, measured in Hertz (Hz] or inverse seconds (s'"), and period (T) is the time for one complete oscillation; thus T = 7- 1 . The amplitude (A] of a wave is the maximum position of the disturbance from an equilibrium position. Nodes are positions along the wave where the amplitude is zero, and antinodes are positions where amplitude variations are at a maximum. Wave disturbances can superimpose on each other when two or more waves arrive at the same position at the same time. The waves may constructively interfere or destructively interfere, depending on the position and phase of each wave as they meet. Standing waves are produced when wave disturbances are confined to a space in which the ongoing and reflected waves within the space form nodes and antinodes at specific positions. For example, standing waves in a tube open at both ends containing air can form such that the wavelength is twice the length of the tube. Standing waves formed on an oscillating string attached at both ends can also form such that the wavelength is twice the length of the string-Equipment and Materials Slinky or other common wave demonstrator (longer spring and tight coils with about a 1-inch diameter) or ball-link chain (2-3 meters in length; 2-3 mm diameter balls. Ball-link chain is good for creating transverse standing wave patterns; it can be found in hardware stores in varying sizes, such as the size used for lamp pull chains.)- Thick string, such as cotton package string (2-3 meters] Video capture device (digital camera, smartphone, etc.). Video analysis or graphical analysis software: This software allows students to wirelessly collect, analyze, and share sensor data from a data sharing source. Meterstick Stopwatch (if video analysis is not available) OPTIONAL: Ring stand, clamps, pulley, and calibrated masses Procedures Part Anchor the Slinky to a fixed end point (another person will work), stretch the Slinky to the right length, send a couple of transverse pulses down the Slinky, and observe what happens at the fixed end. Determine a general rule for the property of wave reflection at a fixed end. Next, take the Slinky and make the other end a "moveable endpoint." This is a little trickier. You can have the Slinky attached to a long pole (broom stick, lab stand pole) and have it able to freely move up and down the pole, which is held vertically by a student or can be mounted on a lab pole stand. You can also hold a Slinky from a height, with the bottom end loose, and send transverse pulses down the Slinky, watching how they reflect at the far end. You then perform the same experiment stated above. You should send a couple of different transverse wave pulses down the Slinky to the moveable end and observe what happens. Compare and contrast with the "fixed end" reflections, and again determine a general rule for these types of reflections. To further refine your observations (and practice for the next part of the set of experiments), create a 5-10 second video of a few of their pulse reflections. This video can be inserted into video analysis software or made on a cell phone or tablet. You can slow down the process of the reflection and determine if your rules make sense and fit the video evidence. Part II Using the same Slinky and video approach, practice sending oncoming pulses towards each other on the long stretched-out Slinky. You should vary the initial conditions; for example, on a horizontal spring, one pulse vertically upward and one pulse vertically downward, both vertically upward, and other possibilities. Or the entire investigation could take place on a smooth tile floor with either longitudinal or sideways transverse pulses. You should strive to obtain a few good sets of video footage and use theMechanical Waves Lab: What are the properties of mechanical waves? analysis tools to understand what happens when the wave pulses are at the same positions on the spring at the same time. You should then try to come up with a general rule for combining waves. Part Ill 1. Design an experimental procedure to determine if there is a relationship between the tension in the Slinky and speed of the wave pulse. 2. Design an experimental procedure to determine if there is a relationship between the amplitude of the wave pulse and the speed of the wave pulse traveling through the Slinky, assuming the tension remains constant during the exercise. 3. Connect thick strings of different mass densities to each other and examine qualitatively how the speed of the wave changes when pulses travel from one string to another. Report Once you have your plan, conducted your plan and collected data, and analyzed the results, you are ready to report your results to your teacher. In your report, you need to include the following: An explanation of the purpose of each part of the lab An explanation of the procedures used for each part of the lab Raw data and representations thereof (ice. graphs, data charts, etc) for each part of the lab A discussion of the results of the laboratory that addresses the purpose of each part of the lab