Kinetic energy is instantaneous, that is to say, the work done by a force to an object in a process is equal to the change of kinetic energy in this process. Kinetic energy is a state quantity without negative value. In an object system where only gravity or elasticity does work, the kinetic energy and potential energy of the object system are transformed into each other, but the total energy of mechanical energy remains unchanged. This law is called the law of conservation of mechanical energy.
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The kinetic energy theorem generally only involves the initial and final state of an object's motion, and the change of the initial and final state can be obtained by the energy conversion when doing work in the process of motion. But the total energy follows the law of conservation of energy, and the transformation of energy includes the changes of kinetic energy, potential energy, heat energy and light energy (not involved in high school).
The so-called kinetic energy simply refers to the energy possessed by an object because of its motion. Numerically equal to (1/2)mv. Kinetic energy is a kind of energy, and its unit in the international system of units is Joule (J), or coke for short.
It should be noted that kinetic energy (and all kinds of work corresponding to it) is scalar, that is, only magnitude has no direction. When summing, only algebraic sum is calculated, which does not conform to the parallelogram law of vectors (mathematically called vectors).