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Magnetism

The Magnetic Field

air friction, Italian physicist, subatomic particles, air resistance, theory of relativity

Mechanics, branch of physics concerning the motions of objects and their response to forces. Modern descriptions of such behavior begin with a careful definition of such quantities as displacement (distance moved), time, velocity, acceleration, mass, and force. Until about 400 years ago, however, motion was explained from a very different point of view. For example, following the ideas of Greek philosopher and scientist Aristotle, scientists reasoned that a cannonball falls down because its natural position is in the earth; the sun, the moon, and the stars travel in circles around the earth because it is the nature of heavenly objects to travel in perfect circles.

The Italian physicist and astronomer Galileo brought together the ideas of other great thinkers of his time and began to analyze motion in terms of distance traveled from some starting position and the time that it took. He showed that the speed of falling objects increases steadily during the time of their fall. This acceleration is the same for heavy objects as for light ones, provided air friction (air resistance) is discounted. The English mathematician and physicist Sir Isaac Newton improved this analysis by defining force and mass and relating these to acceleration. For objects traveling at speeds close to the speed of light, Newton’s laws were superseded by Albert Einstein’s theory of relativity. For atomic and subatomic particles, Newton’s laws were superseded by quantum theory. For everyday phenomena, however, Newton’s three laws of motion remain the cornerstone of dynamics, which is the study of what causes motion.

Contributors

Shwatrz, Clifford E., M.S., Ph.D.

Professor of Physics, State University of New York at Stony Brook. Author of "The Fundamental Particles", "Foundations of Physics", and other books.



Article key phrases:

air friction, Italian physicist, subatomic particles, air resistance, theory of relativity, great thinkers, quantum theory, laws of motion, branch of physics, speed of light, Albert Einstein, cannonball, different point of view, heavy objects, velocity, acceleration, displacement, Mechanics, moon, quantities, behavior, mass, earth, scientists, distance, response, analysis, study, time

 
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