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I've done experiment with spring and mass to determine the natural frequencies of 4 springs. The first experiment went well but I had some problem when I want to test the resonant frequency. I'll explain the context first.

After the spring test, the spring was tested for its resonance frequency using frequency generator, amplifier, and speaker with tube to focus on the wave. I set up the spring stretched vertically and blasting the sound perpendicular to the spring. The string were stretched about 1.7x of its length (it was clamped both side).

In theory the resonance is at 26 Hz but after trying for 4 hours blasting the sound, I can't make the spring in resonance, the same goes for the other 3 springs

What did I do wrong? I still unfamiliar with the correct methods to find the resonant frequency

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  • $\begingroup$ In theory the resonance is at 26 Hz. Where did this value come from? Was the frequency of vertical oscillations of the spring-mass system? $\endgroup$
    – Farcher
    Commented Feb 15, 2023 at 22:38

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The resonant frequency depends just as much on mass density as on stretch and spring constant. You also have to consider whether you are looking at a transverse wave or a longitudinal wave. Blasting from the side is a transverse wave, similar to a wave on a string. A mass hanging from the spring is a longitudinal effect. I don't know what kind of spring you have, but many springs experience a significant change in loop density, and therefore mass density, when oscillating.

Unlike a string, stretching a spring vertically can result in a non-uniform tension and mass density. Loops at the top must support the force due to the stretch and the weight of the spring. If they are further apart than loops at the bottom, tension at the top is greater and mass density is smaller. Both of these would contribute to a greater wave speed at the top than at the bottom. A greater tension would make the spring force a greater effect at the top and make loop distances more uniform.

You don't say enough about your spring to know what does or does not matter most, but these are the first things thatcome to mind.

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  • $\begingroup$ It seems that I got the wrong methods then I got this kind of spring (youtube.com/watch?v=jewSVEBkI_s) But because we don't have the wave generator my friend suggest me to use the speaker If I do like it does in the video, would the mass and the other spring on top disturb or even change the resonance value? $\endgroup$
    – Rizky Aiman
    Commented Feb 15, 2023 at 22:34
  • $\begingroup$ So if I have to do it correctly, does the methods used in this video (youtube.com/watch?v=jewSVEBkI_s) correct? I should have not stretch the spring but instead put a mass like the video I attached above? I just want to test 1 spring, but if I attached another spring on top the mass would it change the resonance value? $\endgroup$
    – Rizky Aiman
    Commented Feb 15, 2023 at 22:37
  • $\begingroup$ Adding another spring would change the resonance frequency. The force from each spring would change in the same direction when the mass move up or down. The change of net force would effectively be due to a spring with a constant equal to the sum of the two spring constants. In the resonance like in the video, the resonant frequency is that of the spring/mass combination, not of the spring itself. This is just sqrt(k/m), in radians per second. Are you looking for the natural frequency of a spring/mass system, or the natural frequency of a standing wave on a spring held tight at both ends? $\endgroup$
    – Ken Mellendorf
    Commented Feb 16, 2023 at 22:59
  • $\begingroup$ I'm looking for the natural frequency of the spring itself and to test the resonance frequency. What should I do? $\endgroup$
    – Rizky Aiman
    Commented Feb 22, 2023 at 3:13
  • $\begingroup$ If you are looking for the natural frequency of a free-hanging spring, then the mass of the coils becomes important. A massless spring with no mass hanging from it would have force due to compression but no mass to provide inertial. Force without inertia would result in chaos. $\endgroup$
    – Ken Mellendorf
    Commented Feb 22, 2023 at 19:48

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