Longitudinal Waves Gizmo Lab ~~Physics
Student Exploration: Longitudinal Waves Vocabulary: antinode, compression, displacement, frequency, interference, longitudinal wave, medium, node, rarefaction, standing wave Prior Knowledge Question (Do this BEFORE using the Gizmo.) In many science fiction movies, an evil alien spaceship explodes with an enormous KABOOM!! Suppose you were floating in space at a safe distance from a large explosion such as the supernova at left. Do you think you would hear anything? Explain. No, I don't think you would hear anything because there is no medium that sound can travel in space. Gizmo Warm-up No sounds can be heard in outer space because sound waves require a medium, such as air, to travel through. Sound waves are examples of longitudinal waves, or waves in which particles move back and forth in the same direction as the wave. You can use the Longitudinal Waves Gizmo to explore the behavior of sound waves. In the Gizmo, an air-filled tube contains 24 evenly-spaced, airtight dividers. To begin, select the Pulsed waves setting and the Open tube. Set the Strength to 1.00. Deselect the graph options at lower right. 1. Click Play ( ) to set off the firecracker by the left end of the tube. What do you see? The 24 evenly-spaced airtight dividers are moving side to side, slowly. 2. Do any individual air molecules travel the length of the tube? Yes, individual air molecules travel the length of the tube. How do you know? Because the tube is open, which means nothing is blocking the air molecules Activity A: Observing longitudinal waves Get the Gizmo ready: ● Click Reset ( ). ● Select Continuous waves. Check that the Strength is 1.00 and Freq. is 30 Hz. Introduction: When you strike a tuning fork on a hard surface, the tines of the fork start to vibrate back and forth at a certain frequency, or number of cycles per second. This motion causes nearby molecules to move back and forth, creating sound waves. The greater the frequency of the sound wave, the higher pitched the sound will be. Question: What happens to air as a sound wave passes through it? 1. Observe: Click Play, and then click Pause ( ) after about 70 simulated milliseconds (does not have to be exact). Sketch the current positions of the dividers below
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