A popular party trick is to fill a glass bottle with water and hit the top of the bottle with an open hand, causing the bottom of the bottle to break open. We investigate the source of the catastrophic cracking through the use of high-speed video and an accelerometer. Upon closer inspection, it is obvious that the acceleration caused by hitting the top of the bottle is followed by the formation of bubbles near the bottom. The nearly instantaneous acceleration creates an area of low pressure on the bottom of the bottle where cavitation bubbles form. Moments later, the cavitation bubbles collapse at roughly 10 times the speed of formation, causing the bottle to break. The accelerometer data shows that the bottle is broken after the bubbles collapse and that the magnitude of the bubble collapse is greater than the initial impact. This fluid dynamics video highlights that this trick will not work if the bottle is empty nor if it is filled with a carbonated fluid because the vapor bubbles fill with the CO 2 dissolved in the liquid, preventing the bubbles from collapsing. A modified cavitation number, including the acceleration of the fluid (a), vapor pressure (P v ), and depth of the fluid column (h), is derived to determine when cavity inception occurs. Through experimentation, visible cavitation bubbles form when the cavitation number is less than 0.5. The experiments, based on the modified cavitation number, reveal that the easiest way to break a glass bottle with your bare hands is to fill it with a non-carbonated, high vapor pressure fluid, and strike it hard. [1]

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When a shock wave reflects off a rigid surface, for certain combinations of shock strength and incident angle to the surface a Mach reflection can occur. This is when the incident and reflected shock waves merge to create a stronger shock wave (called a Mach stem) that travels parallel to the reflecting surface and whose height grows with distance. This phenomenon has been studied extensively for large explosions and for steady shock waves, but is less understood for acoustic weak shocks, where current models for Mach stem formation and growth do not agree with experimental observations. A weak-shock propagation experiment has been conducted at the Bonneville Salt Flats using blast waves generated by acetylene-oxygen filled balloons located at a fixed height above the ground. Analysis of acoustic data at various distances from the source and high-speed camera footage both identify a merging of the direct and ground-reflected waves and the formation of a Mach stem at locations closer to the source than theory would otherwise predict.

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