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Line 1: − + − + − + − When the velocity of the object approaches the speed of light, these expressions need to be modified to account for so-called "relativistic effects". Newtonian mechanics is then no longer a good approximation, and one should use the description given by Einstein's [[Theory of Relativity]]. − −
remove some junk
Force is defined as rate of change of [[momentum]] of a body (F = dp/dt). Unit of force is [[newton]].
Force is defined as rate of change of [[momentum]] of a body (F = dp/dt). A unit of force is the[[newton]].
For non-[[Theory of Relativity|relativistic]] speeds, the momentum is given by ''p = m v'', giving ''F = m a''.<ref>Marcelo Alonso and Edward J. Finn, ''Fundamental University Physics'', Addison-Wesley.</ref> In these expressions, ''F'' stands for the total vector sum of all forces, ''m'' for the mass of the object, ''a'' for its [[acceleration]] expressed as a vector, ''p'' stands for momentum vector and ''v'' for velocity vector. The expression ''F = m a'' is Newton's Second Law, which was stated first by Sir [[Isaac Newton]].
The momentum is given by ''p = m v''. For non-[[Theory of Relativity|relativistic]] speeds, ''F = m a''.<ref>Marcelo Alonso and Edward J. Finn, ''Fundamental University Physics'', Addison-Wesley.</ref> In these expressions, ''F'' stands for the total vector sum of all forces, ''m'' for the mass of the object, ''a'' for its [[acceleration]] expressed as a vector, ''p'' stands for momentum vector and ''v'' for velocity vector.
There are four known fundamental types of forces occurring in nature<ref>Lewis H. Ryder, ''Quantum Field Theory'', 2nd ed., Cambridge University Press, Cambridge (UK), 1996</ref>:
There are four known types of forces occurring in nature<ref>Lewis H. Ryder, ''Quantum Field Theory'', 2nd ed., Cambridge University Press, Cambridge (UK), 1996</ref>:
;[[Electromagnetism|Electromagnetic]] force
;[[Electromagnetism|Electromagnetic]] force