Newtons Laws (AP)

# Newtons Laws (AP) - 3.1 Newton's Laws of Motion:...

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A discussion of Newton’s laws of motion and the concept of equilibrium must include the fundamental forces of nature: gravitational (attractive force between objects due to their mass strong nuclear (force between subatomic particles) electroweak (forces accompanying the process of radioactive decay and the electromagnetic force between electric charges at rest or in motion). Classic physics is concerned with contact forces , the result of physical contact between objects and action-at-a-distance forces , acting through empty space without contact. Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces. Examples of action-at-a-distance forces include gravitational, electric, and magnetic forces. Based on the earlier work of Galileo, in 1867, Newton published in the Principia , the first law of motion (law of inertia): An object at rest will remain at rest or an object in motion will remain in motion in a straight line with a constant velocity unless acted upon by an external unbalanced force. A body is in a state of translational equilibrium whenever the sum of the forces acting on it equals zero thereby conforming to Newton’s first law of motion. The first condition for equilibrium is satisfied when the body is either at rest or moving in a straight line with constant velocity: ∑F=0 whenever a=0 If a body exhibits no acceleration, that is, has no change in motion in one uniformly moving frame of reference, its acceleration must be zero in all such frames of reference. Since objects exhibit no change in motion unless subject to outside influences this is a valid statement in all inertial frames of reference . Inertia describes a body’s resistance to change in motion. By definition, all accelerating reference frames are non-inertial (since Newton’s first law is invalid in these cases). Mass (kg) is a measure of an object’s inertia . This scalar quantity is an inherent property of a body independent of the direction of motion and of the coordinate system used in describing the object’s motion. An object’s weight (N) is equal to the force of gravity acting on the body which varies with location with respect to the Earth’s gravitational field. According to Newton's third law of motion: For every acting force, there exists a reacting force of equal magnitude and opposite direction. The action-reaction force pair referred to in Newton's third law is a set of non- concurrent forces. Two different bodies are exerting two equal but opposite forces on each other. Since each force acts on a different body, the forces do not sum to zero. The implication of Newton’s third law is that there can be no isolated forces.

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Whenever an object rests on a surface, the object will exert a force on the surface, which will in turn according to Newton’s third law, exert a reacting force of equal magnitude in the opposite direction on the object. This
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## This note was uploaded on 04/07/2008 for the course PHYS 101-102 taught by Professor Jelena during the Spring '08 term at Drexel.

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Newtons Laws (AP) - 3.1 Newton's Laws of Motion:...

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