speed
Speed is the physical quantity that describes the movement and direction of the object. The average velocity of an object over a period of time is the ratio of its displacement and time interval during this period: the instantaneous velocity of an object at a given moment is defined as the rate of change of the position vector over time: the object mentioned in physics Speed usually refers to its instantaneous speed. The unit of speed in the international unit system is meters per second, the international symbol is m / s, the Chinese symbol is m / s. In the relativistic framework, the upper speed limit of matter movement is the speed of light. In everyday life, speed and speed are almost synonymous. However, in physics, speed and rate are two different concepts. Speed is the vector, with the size and direction; rate is purely refers to the speed of movement of objects, is scalar, no direction. For example, if a car is traveling at a rate of 60 km / h in the north, its speed is a vector equal to 60 km / h and the direction to the north. The instantaneous velocity of an object is equal to the instantaneous velocity, and the average rate is not necessarily equal to the average speed. ...