Water Impact: When a Sphere Becomes Flat.

A large hydrodynamic force accompanies the vertical impact of bodies on water. While added mass phenomena govern these forces for both spherical and flat impactors, the dynamics of a trapped gas layer critically alters the flat case, reducing the peak pressure below that predicted by water hammer theory. An impactor with a spherical nose cap looks increasingly flat as the nose curvature approaches zero.

Cavitation upon low-speed solid-liquid impact.

When a solid object impacts on the surface of a liquid, extremely high pressure develops at the site of contact. Von Karman's study of this classical physics problem showed that the pressure on the bottom surface of the impacting body approaches infinity for flat impacts. Yet, in contrast to the high pressures found from experience and in previous studies, we show that a flat-bottomed cylinder impacting a pool of liquid can decrease the local pressure sufficiently to cavitate the liquid.

How drain flies manage to almost never get washed away.

Drain flies, Pshycoda spp. (Order Diptera, Family Psychodidae), commonly reside in our homes, annoying us in our bathrooms, kitchens, and laundry rooms. They like to stay near drains where they lay their eggs and feed on microorganisms and liquid carbohydrates found in the slime that builds up over time.