Driven string standing wave experiment

The University of California, Santa Barbara's cord demonstration uses a function generator and mechanical driver loosely attached near a clamped cord end. The other end passes over a pulley to a mass hanger, setting tension. Its photograph shows operation with a strobe; the page reports measured and calculated lowest-mode frequencies. Varying drive frequency at fixed loading selects higher normal modes. This clamp arrangement differs from a string tied directly to a moving driver.^[ref]

A controlled frequency scan holds the cord, endpoint separation and hanging load fixed, then varies frequency slowly to locate large steady amplitudes. Read stationary nodes of a standing wave and count loops; compare the inferred $\lambda =2L/n$ with $c=f\lambda$. As additional checks, compare small drive settings, repeat the scan in reverse, and change only the hanging load to test the predicted square-root tension dependence. These checks test the ideal model rather than adding measurements to the demonstration.

An elastic cord's stretched linear mass density can differ from its relaxed value; the published calculation uses the relaxed value. A strobe can freeze motion at misleading settings, so identify nodes of a standing wave across several snapshots. A moving attachment need not be an exact node of a standing wave. These limits qualify any comparison with ideal fixed-end eigenfrequencies.^[ref]