Physics is Fun 2

WHY does the water jet narrow toward the bottom?

Slow and calm - laminar, as physicists say - the jet from a circular faucet first has a cross-section equal to the inner diameter of the pipe. Under the action of gravity, the flow accelerates, and since the flow of water doesn't change, the jet should narrow.

One can take a different look at it. Among two drops, that came out of the pipe with a small time gap, the first one starts accelerating earlier, and its detachment from the second one is constantly growing. Thus, gravity stretches the jet vertically. Since the volume of water between the drops remains the same, the jet is thinning.

At that, it is compressed by surface tension forces, and when the jet becomes quite thin - 2-3 mm - they also crush it into separate drops.

WHY can't bees fly over mirrors?

In 1963, the Austrian entomologist Herbert Heran and the German behavioral scientist Martin Lindauer noticed something strange about the way honeybees fly through the air. When a group of bees was trained to fly over a lake, they could only fly safely to the other shore if there were waves and ripples on the surface of the water.

At the same time, when the lake was mirror-smooth, the insects suddenly lost their orientation - and even fell into the water. The results of that study confirmed the idea that bees use visual cues to navigate during flight.

In other words, when the surface below the bees is mirrored, the insects assume that the ground below them is much farther away than it really is, and they lower their altitude to the limit.