Sonic booms can occur in fairly routine settings: for example, it is a sonic boom you hear when a whip cracks. But in your bathtub? Apparently, whenever a hard object falls into a pool of water, a jet of air is produced that briefly reaches supersonic speeds .

To study this, physicists at the University of Twente, in the Netherlands, and at the University of Seville set up an experiment in which they plunged a disc-shaped object flat down into water at the relatively leisurely speed of one meter per second. 

Sonic booms can occur in fairly routine settings: for example, it is a sonic boom you hear when a whip cracks. But in your bathtub? Apparently, whenever a hard object falls into a pool of water, a jet of air is produced that briefly reaches supersonic speeds .

To study this, physicists at the University of Twente, in the Netherlands, and at the University of Seville set up an experiment in which they plunged a disc-shaped object flat down into water at the relatively leisurely speed of one meter per second. 

Sonic booms can occur in fairly routine settings: for example, it is a sonic boom you hear when a whip cracks. But in your bathtub? Apparently, whenever a hard object falls into a pool of water, a jet of air is produced that briefly reaches supersonic speeds .

To study this, physicists at the University of Twente, in the Netherlands, and at the University of Seville set up an experiment in which they plunged a disc-shaped object flat down into water at the relatively leisurely speed of one meter per second. 

Here's one you can try at home: Fill a dish with water and drop a small amount of flour onto the surface. The flour particles disperse rapidly, like a tiny starburst, and spread out over the liquid surface. [More]

Editor's note: The original online version of this story was previously posted.

Magnets are remarkable exemplars of fairness--every north pole is invariably accompanied by a counterbalancing south pole. Split a magnet in two, and the result is a pair of magnets, each with its own north and south. For decades researchers have sought the exception--namely, the monopole, magnetism’s answer to the electron, which carries electric charge. It would be a free-floating carrier of either magnetic north or magnetic south--a yin unbound from its yang.