Human sperm is breaking one of Newton's laws of motion and the finding may be revolutionary

Newton's third law of motion is one of the most well-known laws of physics, which states, "For every action, there is an equal and opposite reaction." However, for biological swimmers such as sperm, this may not be the case.

The latest lawbreaker is human sperm, which according to scientists can swim by deforming their bodies in a way that does not elicit a response from their surroundings. Hence, it breaks Newton's third law of motion, they said in a recent study.

To reach this conclusion, they examined data on human sperm cells and Chlamydomonas algae to identify non-reciprocal mechanical interactions that defy Newton's third law. They refer to these interactions as "odd elasticity."

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Hair-like appendages called flagella allow Chlamydomonas and sperm cells to move. These protrude from the cell, resembling a tail. These extend from the cell and help it move forward by changing shape in response to the surrounding fluid. They do so in a non-reciprocal manner, which violates Newton's third law because they do not elicit an equal and opposite reaction from their surroundings.

The elasticity of the flagellum alone does not fully explain how the cell can move. This is where the concept of odd elasticity comes into play. Odd elasticity basically allows the cells to move their flagella without expending a significant amount of energy in their environment, which would have typically hinder their movement.

The ability of a flagellum to wave without suffering significant energy loss increases with a cell's odd elasticity score (or odd elastic modulus), which improves the cell's ability to advance in a manner that defies physics.

Sperm and algae are not the only cells possessing a flagellum; there are likely other rule-breakers out there waiting to be discovered.

Being able to understand and classify other cells or organisms capable of non-reciprocal movement could be very useful, the team behind the study told New Scientist Magazine.

Their approach could help in the design of small elastic robots with the ability to violate Newton's third law, according to one of the study's authors, Kenta Ishimoto of Kyoto University in Japan.

(With inputs from agencies)

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