Impulse

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For other uses, see Impulse (disambiguation).

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In classical mechanics, the impulse of a force is the product of the force and the time during which it acts. Although momentum is conserved within a closed system, individual parts of a system can undergo changes in momentum. Impulse has the same units and dimensions as momentum (kg m/s or N·s = Huygens Hy). The impulse of a time-varying force is calculated as the integral of force with respect to time:

Impulse is the force applied in a unit of time. force x time which equates to change in momentum.

<math>\mathbf{I} = \int \mathbf{F}\, dt </math>

where

I is impulse,

F is the force,

dt is an infinitesimal amount of time.

In the presence of a constant net force, impulse is equal to the average impulse:

<math>\mathbf{I} = m \Delta \mathbf{v} = \mathbf{F}\Delta t </math>

where

m is the mass of the object,

Δv is the change in velocity,

F is the constant net force applied (in order to change the velocity), and

<math>\Delta t</math> is the time interval over which the force is applied.

Using the definition of force yields:

<math>\mathbf{I} = \int \frac{d\mathbf{p}}{dt}\, dt </math>

<math>\mathbf{I} = \int d\mathbf{p} </math>

<math>\mathbf{I} = \Delta \mathbf{p} </math>

In the technical sense, impulse is a physical quantity, not an event or force. However, the term "impulse" is also used to refer to a change in an object's momentum caused by a fast-acting force. This type of impulse is often idealized so that the change in momentum happens with no change in time. This sort of change is a step change, and is not physically possible. However, this is a useful model for certain computations, such as computing the effects of ideal collisions, especially in game physics engines.

[edit] See also

specific impulse
Wave-particle duality defines an impulse for waves. The preservation of momentum at a collision is then called phase matching. Applications include:
- Compton effect
- nonlinear optics
- Acousto-optic modulator
- Umklapp scattering
- electron phonon scattering

[edit] References

Serway, Raymond A.; Jewett, John W. (2004). Physics for Scientists and Engineers, 6th ed., Brooks/Cole. ISBN 0-534-40842-7.
Tipler, Paul (2004). Physics for Scientists and Engineers: Mechanics, Oscillations and Waves, Thermodynamics, 5th ed., W. H. Freeman. ISBN 0-7167-0809-4.