Sperm Defy Newton’s Law of Motion

Sir Isaac Newton’s third law of motion states that for every action there is an equal and opposite reaction. Scientists now understand how human sperm and single-celled algae seemingly defy this law. In research by scientists from Kyoto University and published in PRX Life, they explain how sperm, with their whip-like tails and algal flagella, propel themselves through viscous fluids that should, in theory, resist their movement. Because the cells generate their own energy, they thrust beyond the equilibrium in Newton’s law using an odd elasticity. The researchers believe their understanding of this unique aspect of nature will help in the development of elastic swimming micro-robots that can be used for drug delivery, sensing and microsurgery.