Newton's third law of motion states that for every action, there is an equal and opposite reaction. In the context of a fish swimming through water, this principle can be observed in several ways:
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Fins Pushing Water: When a fish uses its fins to push water backwards, this action creates a force on the water in the opposite direction. According to Newton’s third law, the reaction to this action is that the water exerts an equal and opposite force on the fish, propelling it forward. This is the basic principle of locomotion for the fish.
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Water Pushing Against the Fish's Body: As the fish moves through the water, the water molecules exert forces against the fish's body. While swimming, the fish’s body shapes and contours help to minimize resistance while maximizing the propulsion generated by its movements. The water pushing against the fish is another example of reaction forces at work.
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Swallowing and Expelling Water: When a fish swallows water, it can expel it quickly from its gills or mouth. The act of expelling water pushes it away in one direction, and as a reaction, the expelled water creates a force that pushes (or propels) the fish in the opposite direction.
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Fins Wiggling: When the fish's fins wiggle, they create vortices and alter the flow of water, allowing the fish to push against the water. The reaction to the force exerted on the water results in a forward motion of the fish.
In summary, in swimming, the fish demonstrates Newton's third law through various interactions with water—pushing water backward with its fins leads to a net forward movement, and actions such as swallowing and expelling water also illustrate this fundamental principle of motion.
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