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Force and Motion Force Newton’s First Law Newton’s Second Law Newton’s Third Law Gravitational Force Weight Normal Force pps by C Gliniewicz

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Force is the cause of motion. It can be construed as a push or pull. The study of this subject is called dynamics or Newtonian mechanics. These laws work unless the speeds are very large where relativity starts to be important. The laws also do not apply on an atomic scale where quantum mechanics becomes important. For the vast majority of situations, however, it works well. Newton’s First Law is the Law of Inertia which he took from Galileo. It states that if no force acts on an object, it cannot accelerate and the velocity will not change. Another way of stating the Law of Inertia is that a body at rest remains at rest and a body in motion continues moving in a straight line at constant speed unless a force acts on the object. A force is measured by the acceleration it produces. The net force or resultant force is the vector sum of all the forces acting on an object. An inertial frame of reference is one in which Newton’s Laws hold. A non-inertial frame is any frame where Newton’s Laws do not hold. pps by C Gliniewicz

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Mass is a characteristic that relates a force on a body to the resulting acceleration. Mass has no familiar definition. One only has a sensation of mass when one attempts to accelerate the object. Newton’s Second Law is the Law of Acceleration. It states that the net force on an object is the product of the mass and acceleration. Stated another way, the acceleration of an object is directly proportional to and in the same direction as the force applied to the object and the acceleration is inversely proportional to the mass of the object. The acceleration component along a given axis is caused only by the sum of the force along the same axis. It aids in the solution of a problem to draw a free-body diagram of the situation. One can draw a dot as the object and an arrow pointing in the direction of each force with a length corresponding to the magnitude of the force. This will help in summing the forces to find the net force. If the object consists of a number of bodies, we only worry about external forces on the system of particles and not any internal forces among the particles. pps by C Gliniewicz

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Weight is a force due to gravity which toward the center of the earth. The magnitude of the force is the product of mass and the acceleration of gravity. The normal force is force produced by a surface on which an object rests. The normal force is perpendicular to the surface. Friction is a force which opposes motion. Friction acts parallel to the surface on which the object rests and is perpendicular to the normal force. Tension is a force which exists in a cord, string, rope or other such object. Tension is a pulling force. Newton’s Third Law is the Law of Interaction. When two bodies interact, the forces on the bodies from each other are always equal in magnitude and opposite in direction. pps by C Gliniewicz

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