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- I'd like some others to take a look at our approach here and see where we may be going wrong.
Hi! This project involves both mechanical and electrical elements, so I'm discussing it in this forum since I'm not sure which one it would fit better into.
I'm working on an experiment in which I'm trying to measure the speed of sound through water. The approach is simple: I have a long vertically-positioned PVC pipe filled with water, with two incredibly strong neodymium magnets positioned at either end. The magnet at the bottom is resting on a sponge, and the one at the top is connected to a thinner cylinder that is clamped into position separately from the primary tube. Two coils of wire are positioned outside of the PVC pipe, each one surrounding the places where either magnet is located. When I hit the top of the thinner cylinder with a mallet, in addition to sending a current through the coil that's measured on an oscilloscope, the motion will also send a mechanical shockwave through the water that disturbs the bottom magnet, generating a current through the bottom coil and creating a second signal on the oscilloscope. In theory, the oscilloscope signals can be used to determine how much time it's taken for the wave to travel through the length of the tube.
Anyways, setting this whole thing up, I keep finding speeds in the range of 500 to 700 m/s, usually on the lower end. The distance between the two coils is just under 2 meters, and the time difference between the two signals keeps showing up at about 4.0 ms (sometimes as low as 2.5 ms in certain trials, but rarely). This is interesting, because The Engineering ToolBox puts the speed of sound in room temperature water at around 1481 m/s, and I'm not even breaking half of that.
I decided to ask here because I'm not sure what could be causing this issue, or how to correct for it to improve the experiment. Could the walls of the tube be slowing down the wave through some sort of friction / shear stress effect? Is the vertical positioning of the PVC tube problematic? Is there a general flaw with the approach (e.g. Are we incorrect in thinking that the mechanical wave speed should be the same as the speed of sound)? How can we alter these things?
Thanks!
I'm working on an experiment in which I'm trying to measure the speed of sound through water. The approach is simple: I have a long vertically-positioned PVC pipe filled with water, with two incredibly strong neodymium magnets positioned at either end. The magnet at the bottom is resting on a sponge, and the one at the top is connected to a thinner cylinder that is clamped into position separately from the primary tube. Two coils of wire are positioned outside of the PVC pipe, each one surrounding the places where either magnet is located. When I hit the top of the thinner cylinder with a mallet, in addition to sending a current through the coil that's measured on an oscilloscope, the motion will also send a mechanical shockwave through the water that disturbs the bottom magnet, generating a current through the bottom coil and creating a second signal on the oscilloscope. In theory, the oscilloscope signals can be used to determine how much time it's taken for the wave to travel through the length of the tube.
Anyways, setting this whole thing up, I keep finding speeds in the range of 500 to 700 m/s, usually on the lower end. The distance between the two coils is just under 2 meters, and the time difference between the two signals keeps showing up at about 4.0 ms (sometimes as low as 2.5 ms in certain trials, but rarely). This is interesting, because The Engineering ToolBox puts the speed of sound in room temperature water at around 1481 m/s, and I'm not even breaking half of that.
I decided to ask here because I'm not sure what could be causing this issue, or how to correct for it to improve the experiment. Could the walls of the tube be slowing down the wave through some sort of friction / shear stress effect? Is the vertical positioning of the PVC tube problematic? Is there a general flaw with the approach (e.g. Are we incorrect in thinking that the mechanical wave speed should be the same as the speed of sound)? How can we alter these things?
Thanks!