Schools of fish swim using the same physics principles as cut-throat Tour de France pedal pushers — the weaker fish and bicyclists at the back of the pack use fluid dynamics to keep up.

A shimmering school of fish and a group of sweaty guys in tight shorts have at least one thing in common: an established pecking order. Sure, the ones out in front get the glory, but the ones in back get the easier ride. Fluid dynamics work in both liquids and gases, and are taken advantage of by both undersea creatures outrunning sharks and surface dwellers zooming through the French countryside.


Those leading a group of fish (or cyclists) get hit in the face and body with every molecule in their path. Unless the current (or wind) is with them, those molecules are standing still when the moving creature smashes into them. The molecules are accelerated quickly and tumble up and over the moving animal.

Once the first animal is gone, they don't just return to their original place, or their original motion. Moving objects leave a slipstream behind them. They push fluid out of their way, leaving hollows behind. As more fluid rushes into the hollow, it moves in the same direction the object was moving in. If there are enough objects creating enough slipstreams, they're essentially creating their own "current" behind them. The current moves the same direction (and the same speed) that they do. So anyone taking up the rear will not be smashing into stationary molecules. They'll be moving with an already-established flow set up by their peers.

This slipstream phenomenon has been taken advantage of by racers, but it looks like nature beat them to it. Researchers in the UK recently tested the theory by having a group of fish all swim in the same direction against a current. The same fish (the weaker swimmers) took up the rear of the school every single time. By measuring the fishes' respiration and the strokes of their tails, the researchers estimated that the fish at the back were using 12% less energy than the rest. Although they didn't get a lot of food, they did manage to push along in the safety of the herd without using up the calories from the food they did find. Sometimes it pays to be beta.


[Via The Guardian]