No, the application of those equations to practical problems is patentable. A physics problem is not necessarily practical (2 frictionless spheres in a vacuum are rolling towards each other...), but practical mechanical problems necessarily have a physical aspect and frequently rely on results of solving mathematical formulae. A patent on a mechanical solution may very well include the solution of such equations, and always have. Funny, doesn't look to me like the mechanical industry is stuck in the 1700s.

Edit: An early example of a mechanical "algorithm" patent - http://www.google.com/patents/US3765263