Difference between revisions of "Force"
Aulis Eskola (talk | contribs) (unit newton) |
(remove some junk) |
||
| Line 1: | Line 1: | ||
| − | Force is defined as rate of change of [[momentum]] of a body (F = dp/dt). | + | 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''. 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 | ||
Revision as of 00:58, July 6, 2007
Force is defined as rate of change of momentum of a body (F = dp/dt). A unit of force is thenewton.
The momentum is given by p = m v. For non-relativistic speeds, F = m a.[1] 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[2]:
- Electromagnetic force
- Gravitational force
- Strong force
- this is the force that keeps atomic nuclei together.
- Weak force
- this force is (amongst other things) involved in beta decay, in which a neutron in an atomic nucleus is changed to a proton, emitting an electron and a neutrino.
It should be noted that the latter two forces have an extremely short range (on the order of femtometers), and that a classical (Newtonian or relativistic) description of these forces is not possible. They can only be desribed using quantum field theory, a relativistic version of quantum mechanics.