<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Newton's laws of motion are three physical laws that, together, laid the foundation for classical mechanics . They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces . More precisely, the first law defines the force qualitatively, the second law offers a quantitative measure of the force, and the third asserts that a single isolated force doesn't exist . These three laws have been expressed in several different ways, over nearly three centuries, and can be summarised as follows: </P> <Table> <Tr> <Td> First law: </Td> <Td> In an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force . </Td> </Tr> <Tr> <Td> Second law: </Td> <Td> In an inertial reference frame, the vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration a of the object: F = ma . (It is assumed here that the mass m is constant--see below .) </Td> </Tr> <Tr> <Td> Third law: </Td> <Td> When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body . </Td> </Tr> </Table>

State newton's first and second law of motion