Sperm, when moving, bypasses Newton's law
The oscillations of flagella circumvent the law of equal action and counteraction - Newton's third law - when moving in a viscous medium.Researchers from Kyoto University studied the movements of sperm and other microscopic biological swimmers to find out how they glide through substances that theoretically should resist their movement. The analysis showed that the movements of the flagella overcome the reaction of the medium due to Newton's third law.
Newton's third law states that every action has an equal and opposite counteraction. In their experiments, the researchers noticed that some algae and sperm move with less force than they should. They move in viscous media, which means that it takes effort to swim through them.
By studying the movement of Chlamydomonas algae and human sperm under a microscope, the researchers found that both species used flagella to move. They made wave-like motions, pushing the microfloats through the liquid. Such movements, the scientists said, should cause the fluid to react according to Newton's third law and slow down. But it didn't.
The scientists found that the flagellates move in a certain way to conserve energy. By bending slightly wavelike in response to the fluid's motion, the flagella prevent an equal and opposite reaction, thereby conserving their owner's energy. Modeling the movement of the flagella will allow the same principle to be used to create tiny robotic swimmers, the researchers believe.