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motion
motion the change of position of one body with respect to another. The rate of change is the speed of the body. If the direction of motion is also given, then the velocity of the body is determined; velocity is a vector quantity, having both magnitude and direction, while speed is a scalar qu...
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proper motion
proper motion in astronomy, apparent movement of a star on the celestial sphere , usually measured as seconds of arc per year; it is due both to the actual relative motions of the sun and the star through space. Proper motion reflects only transverse motion, i.e., the component of motion across th...
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inertia
inertia , in physics, the resistance of a body to any alteration in its state of motion , i.e., the resistance of a body at rest to being set in motion or of a body in motion to any change of speed or change in direction of motion. Inertia is a property common to all matter. This property was first...
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precession of the equinoxes
precession of the equinoxes westward motion of the equinoxes along the ecliptic . This motion was first noted by Hipparchus c.120 BC The precession is due to the gravitational attraction of the moon and sun on the equatorial bulge of the earth, which causes the earth's axis to describe a cone in...
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dynamics
dynamics branch of mechanics that deals with the motion of objects; it may be further divided into kinematics, the study of motion without regard to the forces producing it, and kinetics, the study of the forces that produce or change motion. Motion is caused by an unbalanced force acting on ...
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Lorentz contraction
Lorentz contraction , in physics, contraction or foreshortening of a moving body in the direction of its motion, proposed by H. A. Lorentz on theoretical grounds and based on an earlier suggestion by G. F. Fitzgerald; it is sometimes called the Fitzgerald, or Lorentz-Fitzgerald, contraction. The Lor...
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relativity
relativity physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference. One consequence of the theory is that space and time are no longer viewed as separate, independent entities but...
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motion sickness
motion sickness waves of nausea and vomiting experienced by some people, resulting from the sudden changes in movement of a vehicle. The ailment is also known as seasickness, car sickness, train sickness, airsickness, and swing sickness. The principal cause of the disturbance is the effect of motio...
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Newton's laws of motion
Newton's laws of motion Three laws published in 1687 by I.Newton concerning the motion of bodies:1.A body continues in a state of uniform rest or motion unless acted upon by an external force.2.The acceleration produced when a force acts is directly proportional to the force and takes place in the ...
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equinox
equinox , either of two points on the celestial sphere where the ecliptic and the celestial equator intersect. The vernal equinox, also known as "the first point of Aries," is the point at which the sun appears to cross the celestial equator from south to north. This occurs about Mar. 21, ma...
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