<p>Vibration is recognized as an effective method for reducing friction. However, the underlying mechanisms governing friction reduction at different frequencies remains to be investigated. This study presents an experimental investigation into the frequency-dependent characteristics of friction reduction induced by normal vibration, covering a broad frequency range. At low frequencies, friction is significantly reduced only when macroscopic stick-slip and friction reversal occur, otherwise, the reduction in friction is limited. At high frequencies, vibration can reduce friction significantly, even in the absence of macroscopic stick-slip and friction reversal. Despite these distinct observations, the mechanism of friction reduction across the broad frequency range can be unified by the normal vibration velocity amplitude, which serves as a universal criterion for scaling friction reduction across frequencies. A further comparison with prior microscopic results reveals similar phenomena at both macro-scale and micro-scale.</p>