An Experiment on Newtons Third Law Couple two spring balances A and B as shown in the figure. When we pull the balance B both the balances show the same reading indicating that both the action and reaction forces are equal and opposite. In this case, the pull of either of the two spring balances can be regarded as action and that of the other balance as the reaction. In the second experiment, two people pull on two spring scales. Regardless of who tries to pull harder, the two forces as measured on the spring scales are equal. Interposing the two spring scales is necessary in order to measure the forces, but the outcome is not some artificial result of the scales interactions with each other. If one person slaps another hard on the hand, the slappers hand hurts just as much as the slappees, and it doesnt matter if the recipient of the slap tries to be inactive. (Punching someone in the mouth causes just as much force on the fist as on the lips. Its just that the lips are more delicate. The forces are equal, but not the levels of pain and injury.) Newton, after observing a series of results such as these, decided that there must be a fundamental law of nature at work: Newtons third law Forces occur in equal and opposite pairs: whenever object A exerts a force on object B, object B must also be exerting a force on object A. The two forces are equal in magnitude and opposite in direction. In one-dimensional situations, we can use plus and minus signs to indicate the directions of forces, and Newtons third law can be written succinctly as FA on B = -FB on A. There is no cause and effect relationship between the two forces. There is no original force, and neither one is a response to the other. The pair of forces is a relationship, like marriage, not a back-and-forth process like a tennis match. Newton came up with the third law as a generalization about all the types of forces with which he was familiar, such as frictional and gravitational forces. When later physicists discovered a new type force, such as the force that holds atomic nuclei together, they had to check whether it obeyed Newtons third law. So far, no violation of the third law has ever been discovered, whereas the first and second laws were shown to have limitations by Einstein and the pioneers of atomic physics. wla na koy makit.an para sa mag kagrupo naku sa science
Posted on: Sat, 28 Jun 2014 02:45:22 +0000
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