In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are vector quantities. The orientation of an object's acceleration is given by the orientation of the net force acting on that object. The magnitude of an object's acceleration, as described by Newton's Second Law, is the combined effect of two causes:

• the net balance of all external forces acting onto that object — magnitude is directly proportional to this net resulting force;
• that object's mass, depending on the materials out of which it is made — magnitude is inversely proportional to the object's mass.

किसी वस्तु के वेग में परिवर्तन की दर को त्वरण कहते हैं। इसका मात्रक मीटर प्रति सेकेण्ड² (m/s²) होता है तथा यह एक सदिश राशि हैं।