JAPAN: Scientists have found that sperm and certain types of algae break one of the fundamental rules of physics—Newton’s third law of motion. This finding, which has taken the scientific community by surprise, sheds new light on the fascinating and complex world of biological motion.
Newton’s third law
Newton’s third law of motion is a fundamental principle in physics. It states that for every action, there is an equal and opposite reaction. In other words, when you push something, it pushes back with the same force, and this law governs how objects move in our everyday world.
The Law-breakers: Sperm and algae
Recent research has revealed that tiny biological swimmers, such as sperm and Chlamydomonas algae, don’t follow this fundamental law. They can swim by deforming their bodies in a unique way that doesn’t trigger an equal and opposite reaction from their surroundings. In simpler terms, they can move without using the typical amount of energy expected.
Understanding odd elasticity
To understand this phenomenon, scientists examined data from human sperm cells and Chlamydomonas algae. These cells have hair-like appendages called flagella that allow them to move. These flagella extend from the cell and change shape in response to their environment, helping the cell move forward.
What’s interesting is that these flagella move in a non-reciprocal way, meaning they don’t follow the rule of equal and opposite reactions as described by Newton’s law. This behavior is made possible by a concept known as “odd elasticity.” It allows these cells to swim without expending much energy, which would typically slow them down.
Practical implications and future research
The discovery of this odd elasticity in biological swimmers opens up intriguing possibilities. Understanding and classifying other cells or organisms with similar abilities could be valuable in various applications. This unique way of moving might even be used in designing small elastic robots that can defy Newton’s third law, as suggested by Kenta Ishimoto of Kyoto University in Japan, one of the study’s authors.
Scientists are excited about this because it challenges what we know about how things move and could have important uses, like making small robots that move in a similar, energy-efficient way. So, in the world of biology, some intriguing rule-breakers continue to astonish us.
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