加速度

In physics, acceleration is a measure of how fast and in what direction an object's speed and direction of motion are changing. It is defined as the rate of change of the velocity. Like velocity, acceleration has a magnitude and a direction, making it a vector quantity. The SI unit for acceleration is metre per second squared (m⋅s−2, m/s2).The tangential acceleration of an object is the component of the acceleration which is in the same direction as the motion (or tangential velocity) of the object. When the velocity of the object does not change direction, this is called linear acceleration. Deceleration or retardation, on the other hand, is the component of the acceleration in the opposite (or antiparallel) direction to the tangential velocity. Radial acceleration or normal acceleration (or centripetal acceleration during circular motions) is the component of the acceleration that changes the direction of the object's velocity. In Newtonian mechanics, the acceleration of a mass arises from forces acting on it, with its net acceleration being a result of the net force acting on it. By Newton's second law, the magnitude of the net acceleration will be proportional to the magnitude of the net force acting on the object and inversely proportional to the mass of the object, while the direction of the net acceleration will be the same as the direction of the net force.