why do mirrors make noise
The Short AnswerMirrors make noise due to the rapid expansion and contraction of the glass and its coating when exposed to temperature changes. This physical stress causes the materials to vibrate, producing the subtle creaking or popping sounds often heard.
The Science Behind It
The 'noise' mirrors make is primarily a result of thermal expansion and contraction. Glass, like most materials, expands when heated and contracts when cooled. The reflective coating (usually aluminum or silver) also undergoes similar changes. When a mirror's temperature changes unevenly, different parts of the glass and coating expand or contract at slightly different rates. This differential stress creates internal tensions within the material. As these stresses build and release, the material vibrates minutely, much like a stressed beam bending. These vibrations are transmitted through the glass and air, which we perceive as faint creaking, popping, or ticking sounds. The effect is more noticeable in older mirrors or those exposed to significant temperature fluctuations, such as near a window on a sunny day or in a bathroom experiencing steam.
Fun Facts
- The sounds are often referred to as 'audible thermal expansion'.
- Older mirrors with thicker glass and older reflective coatings may exhibit these sounds more prominently.