In physics and other sciences, energy is a scalar physical quantity that is a property of objects and systems which is conserved by nature. Energy is often defined as the ability to do work. Several different forms of energy, including kinetic, potential, thermal, gravitational, sound energy, light energy, elastic, electromagnetic, chemical, nuclear, and mass have been defined to explain all known natural phenomena.
While one form of energy may be transformed to another, the total energy remains the same. This principle, the conservation of energy, was first postulated in the early 19th century, and applies to any isolated system. According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time.
In physics, a force is a push or pull that can cause an object with mass to accelerate. Force has both magnitude and direction, making it a vector quantity. According to Newton's Second Law, an object will accelerate in proportion to the net force acting upon it and in inverse proportion to the object's mass.
Since antiquity, scientists have used the concept of force in the study of stationary and moving objects. These studies culminated with the descriptions made by the third century BC philosopher Archimedes of how simple machines functioned. The rules Archimedes determined for how forces interact in simple machines are still a part of modern physics. Earlier descriptions of forces by Aristotle incorporated fundamental misunderstandings, which would not be resolved until the 17th century when Isaac Newton correctly described how forces behaved. Newtonian descriptions of forces remained unchanged for nearly three hundred years.
In physics, motion means a continuous change in the location of a body. Change in motion is the result of applied force. Motion is typically described in terms of velocity, acceleration, displacement, and time. An object's momentum is directly related to the object's mass and velocity, and is conserved within a system, as described by the law of conservation of momentum. Everything in the universe is moving. As there is no absolute reference system, absolute motion cannot be determined and only motion relative to a point of reference can be determined; this is emphasised by the term relative motion.
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