Sperm has been caught breaking the law – Newton’s third law of motion

The laws of physics have been violated (or appear to have been violated) by all sorts of things, from balancing rocks to a Seinfeld apartment, and now by human sperm. The latest lawbreakers are defying Newton’s third law of motion, distorting their bodies while swimming in a way that elicits no response from their surrounding environment.

Newton’s third law states that when one body exerts a force on another body, the second body exerts an equal and opposite force on it. In other words: “For every action, there is an equal and opposite reaction.” However, for biological swimmers such as sperm, this may not be the case.

In a new study, scientists analyzed Chlamydomonas Algae and data on human sperm cells, identify non-reciprocal mechanical interactions, which they call “individual plasticity”, which contradict Newton’s third law.

both of them Chlamydomonas Sperm cells use hair-like appendages called flagella to move around. They protrude from the cell, almost like a tail, which helps propel them forward by changing shape as they interact with the surrounding fluid. They do so in a non-reciprocal manner, meaning that they do not elicit an equal and opposite response from their surroundings and, therefore, violate Newton’s third law.

However, flagellar flexibility does not fully explain how a cell is able to move, and this is where strange flexibility comes into play. This allows cells to vibrate their flagella without expending too much energy on their surroundings, which would otherwise inhibit their movement. .

The higher a cell’s degree of individual elasticity (or individual modulus of elasticity), the more the flagellum can undulate without significant loss of energy, and thus the more capable the cell is of moving forward—in a way that defies physics.

Sperm and algae aren’t the only cells to have flagella – many microorganisms have flagella (they can make bacteria look like they’re playing little drums) – which means another rule-breaking is likely to be discovered. The team behind the study said the ability to understand and classify cells or other organisms capable of non-reciprocal movement could be very useful. new world.

Their approach could also help design small, flexible robots that have the potential to break Newton’s third law, according to one of the study’s authors, Kenta Ishimoto of Kyoto University in Japan.

Furthermore, the individual elastic modulus can be calculated for any closed-loop system, which means it can be applied to a wide range of biological data, including active elastic membranes and bulk dynamics, the authors explain in their conclusion.

Breaking the law was never helpful.

The study is published in Hyatt PRX.

[H/T: New Scientist]