Al Tobias (wat4y) - Office: Rm. 201, (434) 924-0538 - Lab: Rm. 202, (434) 924-6800
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
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Purpose:To demonstrate that the standing waves in an air column are indeed the longitudinal waves and the regions of high and low pressure can be used to suspend/levitate light objects against gravity
Procedure:Clamp a 9" speaker with focusing "horn" to the desk and vertically place a transparent Plexiglas pipe over the horn opening. Connect the speaker to the PASCO wave generator and induce the resonance in the pipe air column. Drop a piece of Styrofoam (about half standard size packing peanut) into the tube. Watch it levitate. Demonstrate that the Styrofoam drops when off the resonance frequency. One can also excite a second harmonic and suspend the object in a different node (in the middle of the tube)
Hints:1m column of air has the main resonance frequency at about 175Hz and second harmonic at about 350Hz. First harmonics will levitate at the top of the column. One can shift the suspension point from the top of the tube to the middle by quickly covering the tube with the palm of the hand and releasing it when Styrofoam approaches the mid point of the pipe. Play w/ the generator frequency to achieve more stable levitation. Use 2 large clamps to affix the speaker to the table.