Identifying these laws is like recognizing patterns in nature from which further patterns can be discovered. The idea of generally applicable or universal laws is important-it is a basic feature of all laws of physics. Experiments have verified that any change in velocity (speed or direction) must be caused by an external force. Newton’s first law is general and can be applied to anything from an object sliding on a table to a satellite in orbit to blood pumped from the heart. When the air is off, friction quickly slows the puck but when the air is on, it minimizes contact between the puck and the hockey table, and the puck glides far down the table. Third law To every action, there is always opposed an equal reaction or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.\): An air hockey table is useful in illustrating Newton’s laws. Newton's second law has also been regarded as setting out a research program for physics, establishing that important goals of the subject are to identify the forces present in nature and to catalogue the constituents of matter. ![]() If the body's location as a function of time is s ( t ) into Newton's second law, an equation with predictive power can be written. For example, a body might be free to slide along a track that runs left to right, and so its location can be specified by its distance from a convenient zero point, or origin, with negative numbers indicating positions to the left and positive numbers indicating positions to the right. Its position can then be given by a single number, indicating where it is relative to some chosen reference point. The simplest case is one-dimensional, that is, when a body is constrained to move only along a straight line. Movement is represented by these numbers changing over time: a body's trajectory is represented by a function that assigns to each value of a time variable the values of all the position coordinates. The mathematical description of motion, or kinematics, is based on the idea of specifying positions using numerical coordinates. ![]() For instance, the Earth and the Sun can both be approximated as pointlike when considering the orbit of the former around the latter, but the Earth is not pointlike when considering activities on its surface. This is a reasonable approximation for real bodies when the motion of internal parts can be neglected, and when the separation between bodies is much larger than the size of each. Newton's laws are often stated in terms of point or particle masses, that is, bodies whose volume is negligible. Limitations to Newton's laws have also been discovered new theories are necessary when objects move at very high speeds ( special relativity), are very massive ( general relativity), or are very small ( quantum mechanics). ![]() In the time since Newton, the conceptual content of classical physics has been reformulated in alternative ways, involving different mathematical approaches that have yielded insights which were obscured in the original, Newtonian formulation. Newton used them to investigate and explain the motion of many physical objects and systems, which laid the foundation for classical mechanics. The three laws of motion were first stated by Isaac Newton in his Philosophiæ Naturalis Principia Mathematica ( Mathematical Principles of Natural Philosophy), originally published in 1687. If two bodies exert forces on each other, these forces have the same magnitude but opposite directions.When a body is acted upon by a net force, the body's acceleration multiplied by its mass is equal to the net force. ![]() A body remains at rest, or in motion at a constant speed in a straight line, unless acted upon by a force.These laws can be paraphrased as follows: Newton's laws of motion are three basic laws of classical mechanics that describe the relationship between the motion of an object and the forces acting on it.
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