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Sperm caught breaking Newton's third law of motion

Some biological cells swim freely in a way that apparently breaks one of Newton’s laws of motion – but only if they have strange elastic properties

By Karmela Padavic-Callaghan

20 October 2023

human sperms

Human sperm cells are law-breakers


Human sperm cells and some microorganisms swim by deforming their bodies in a way that breaks Newton’s third law of motion – and we’re closer to understanding how they do it. The findings could eventually inspire researchers to develop tiny robots that also violate this law as they swim.

Famously, Newton’s third law can be summed up in the phrase “for every action, there is an equal and opposite reaction”. This means that as you push against a wall, the wall pushes back on you.…

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