Equations of motion modification consistent with conservation of momentum, see variable-mass system. It may be simple to write down the equations of motion in vector form using Newton's laws of motion, but the components may vary in complicated ways with spatial coordinates and time, and solving them is not easy. Often there is an excess of variables to solve for the problem completely, so Newton's laws are not always the most efficient way to determine the motion of a system. In simple cases of rectangular geometry, Newton's laws work fine in Cartesian coordinates, but in other coordinate systems can become dramatically complex. The
Valerio-Horatian Laws on the plebiscites, there were three instances of such law. There were two other laws on appeal which were proposed by two consuls who were also members of the Valeria family, one by Publius Valerius Publicola in 509 BC and one by Marcus Valerius Corvus in 300 BC. Two other laws which provided for the plebiscites to be binding on the whole people were also proposed, one by Quintus Publilius Philo in 339 BC and one by Quintus Hortensius in 287 BC. This has led some historians to argue that in both cases the first and second laws are unhistorical