Difference between revisions of "Force"
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| − | '''Force''' is defined as rate of change of [[momentum]] of a body | + | '''Force''' is defined as rate of change of [[momentum]] of a body <math>\vec F = {d \vec p \over dt} </math>. The [[International System of Units|SI]] unit of force is the [[newton]] and the [[US customary system]] unit is the pound. |
| − | The momentum of an object is given by | + | The momentum of an object is given by <math> \vec p = m \vec v</math>. For non-[[Theory of Relativity|relativistic]] speeds, <math> \vec F = m \vec a </math> when mass can be assumed to be constant.<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 fundamental types of forces occurring in nature<ref>Lewis H. Ryder, ''Quantum Field Theory'', 2nd ed., Cambridge University Press, Cambridge (UK), 1996</ref>: | ||
Revision as of 03:13, October 31, 2007
Force is defined as rate of change of momentum of a body . The SI unit of force is the newton and the US customary system unit is the pound.
The momentum of an object is given by Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \vec p = m \vec v} . For non-relativistic speeds, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \vec F = m \vec a } when mass can be assumed to be constant.[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
- The force that acts on objects with electric charge.
- Gravitational force
- The force that attracts any two objects with mass.
- Strong force
- The force that keeps atomic nuclei together.
- Weak force
- This force is 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 described using quantum field theory, a relativistic version of quantum mechanics.