Everything that can vibrate has a natural frequency, a specific frequency at which it oscillates most easily and in the absence of disturbance. The relationship between natural frequency and weight (mass) is inverse: increasing the mass of an object will decrease its natural frequency, and decreasing the mass will increase its natural frequency. Why? Well, because natural frequency is determined by both the mass and stiffness of a system, and a higher mass for a given design generally makes it harder for the object to oscillate at a given frequency…
When designing something, if you get natural frequency wrong you can have big ass problems. If the external force's frequency approaches the system's natural frequency, a phenomenon called “mechanical resonance” occurs. This causes the system to vibrate with a much larger amplitude, potentially leading to excessive stress, material fatigue, and even structural failure…
In many physics textbooks, the failure of the Tacoma Narrows Bridge in 1940 is blamed on natural frequency or presented as an example of forced mechanical resonance, but it’s more complicated than that. The bridge collapsed because winds produced "aeroelastic flutter", which is another thing altogether, that was self-exciting and unbounded...