Measuring the frequency of a tuning fork?

Question

How would I measure the frequency of a tuning fork that was unmarked?

thank you

Answer 1

Here's a convoluted method that makes use of an elaborate setup:

First, set up a graduated tube (a long one, preferably) in a bucket or something else and fill the tube somewhat with water. Near the bottom of the tube, drill a small hole, and insert a rubber pipe, which should be connected at the other end to a small bucket filled also somewhat with water. This allows you to adjust the water level accordingly. Have someone hold the water-filled tube steady or attach it to a rigid surface to keep it from wobbling. Now, hit the tuning fork and hold it above the surface of the tube to let the tube resonate. You have set up a standing wave of the first harmonic.

Moving the small bucket up and down to change the water level, find the water level at which the tube resonates the loudest. This will yield 1/4th of the wavelength of the standing wave (the distance from the water level to the top of the tube). Since frequency = speed/wavelength, you can use v = 345 m/s and the calculated wavelength to find the frequency of your tuning fork.

Answer 2

Scarlet’s answer is a good idea. However, you may find this a little easier. See if you can get hold of a hollow tube about a foot long. Longer would be better but a foot should be long enough. A paper towel tube would work but it is a bit too big. If you could get a PVC pipe about a half inch in diameter that would be perfect.

Now, rather than drill the hole and attach the rubber hose, all you need do is fill a deep sink or a mop bucket full of water and place the hollow tube so that the bottom is just in the water. Carefully strike your tuning fork on your knee or something soft like that. DO NOT strike the tuning fork on a hard surface like a table top.

Now, hold the tuning fork over the opening of the hollow tube near but not touching the hollow tube. Hold it so that the tines are one below the other. In other words the tuning fork should be vibrating vertically, not horizontally over the opening of the hollow tube.

Move the hollow tube slowly into the water and listen carefully. At some point you will hear that pitch of the tube get noticeably louder. There will be no doubt in your mind when you hear this amazing phenomenon!

When this happens you know that you have found the length of the tube that is exactly one forth the length of the fundamental wave of the tuning fork. Measure this length in meters. More likely you will have centimeters. Convert this to meters by moving the decimal point to the left two places. If the tube is 16cm, the length you will use in your calculations will 0.16m.

Now you can do as Scarlet said. Divide four times the length of the hollow tube that is sticking out of the water into 345m/s and you will have your frequency.