- Relative velocity
In

kinematics ,**relative velocity**is the vector difference between the velocities of two objects, as evaluated in terms of a singlecoordinate system , usually aninertial frame of reference unless specifically stated otherwise.For example, if the velocities of particles A and B are v

_{A}and v_{B}respectively in terms of a given inertial coordinate system, then the relative velocity of A with respect to B (also called the velocity of A relative to B) is v_{A}– v_{B}. Conversely the velocity of B relative to A is v_{B}– v_{A}. If no other system of coordinates is specified, the expression “velocity of A relative to B” is usually understood as shorthand for “the velocity of A in terms of an inertial coordinate system with respect to which B is at rest”.In two dimensions, relative velocities can be calculated by the parallelogram law of addition of vectors. We can take one velocity in opposite direction and then add it to the other velocity vector by the parallelogram law of vectors.

**A**

**-B**

__________|_____________________**B**If we suppose the vertical line A as one velocity Vector and the Line B as the other velocity vector.Then the relative velocity vector of these velocities will be the sum of vectors A and -B.which will go in between A and -B by the parallelogram law of vector addition.In Galilean kinematics (i.e., not accounting for the effects of special relativity), the relative velocity between two particles is the same with respect to any system of inertial coordinates. This is because changing from one inertial coordinate system to another (according to Galilean kinematics) simply adds a common increment vector to each velocity vector, so the difference between any pair of velocities is unaffected. However, taking the effects of

special relativity into account, the relative velocity between two particles actually depends on the inertial coordinate system in terms of which the individual velocities are evaluated. This is because the effect of changing from one system of inertial coordinates to another is more complicated than simply adding a common increment vector to each velocity vector.Oversimplified: The velocity of object A, minus the velocity of object B, equals their 'relative velocity'.

**References*** Alonso & Finn, “Fundamental University Physics“ Volume 1 , Addison-Wesley.

* Greenwood, Donald T, “Principles of Dynamics”.

* Goodman and Warner, “Dynamics”.

* Beer and Johnston, “Statics and Dynamics”.

* McGraw Hill Dictionary of Physics and Mathematics.

* Rindler, W., “Essential Relativity”.**ee also***

Special relativity

*Classical mechanics

*Velocity

*Parallelogram Law of addition of vectors **External links*** [

*http://hyperphysics.phy-astr.gsu.edu/Hbase/relmot.html Relative Motion at HyperPhysics*]

* [*http://physics.bu.edu/~duffy/java/RelV2.html A Java applet illustrating Relative Velocity, by Andrew Duffy*]

*Wikimedia Foundation.
2010.*

### Look at other dictionaries:

**Relative velocity**— Velocity Ve*loc i*ty, n.; pl. {Velocities}. [L. velocitas, from velox, ocis, swift, quick; perhaps akin to v?lare to fly (see {Volatile}): cf. F. v[ e]locit[ e].] [1913 Webster] 1. Quickness of motion; swiftness; speed; celerity; rapidity; as,… … The Collaborative International Dictionary of English**relative velocity**— santykinis greitis statusas T sritis Standartizacija ir metrologija apibrėžtis Dydis, išreiškiamas judančiojo kūno ir atskaitos greičių dalmeniu. atitikmenys: angl. non dimensional velocity; relative velocity vok. Geschwindigkeitsverhältnis, n;… … Penkiakalbis aiškinamasis metrologijos terminų žodynas**relative velocity**— santykinis greitis statusas T sritis fizika atitikmenys: angl. dimensionless velocity; relative velocity vok. bezogene Geschwindigkeit, f; relative Geschwindigkeit, f rus. относительная скорость, f pranc. vitesse adimensionnelle, f; vitesse… … Fizikos terminų žodynas**relative velocity**— santykinis greitis statusas T sritis Standartizacija ir metrologija apibrėžtis Tekėjimo greičio tam tikrame taške ir tuo pačiu metu išmatuoto pamatinio greičio atitinkamame taške (pvz., greičio ašyje) arba vidutinio ašinio skysčio arba dujų… … Penkiakalbis aiškinamasis metrologijos terminų žodynas**relative velocity**— reliatyvusis greitis statusas T sritis fizika atitikmenys: angl. relative velocity vok. relative Geschwindigkeit, f rus. скорость относительно ..., f pranc. vitesse relative, f … Fizikos terminų žodynas**relative velocity**— noun : the vector difference between the velocities of two bodies : the velocity of a body with respect to another regarded as being at rest compare relative motion … Useful english dictionary**Velocity**— Ve*loc i*ty, n.; pl. {Velocities}. [L. velocitas, from velox, ocis, swift, quick; perhaps akin to v?lare to fly (see {Volatile}): cf. F. v[ e]locit[ e].] [1913 Webster] 1. Quickness of motion; swiftness; speed; celerity; rapidity; as, the… … The Collaborative International Dictionary of English**Relative**— can refer to: *Kinship, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are said to be relatives Physics*Relativity as a concept in physics (for example Albert Einstein s… … Wikipedia**Velocity**— In physics, velocity is defined as the rate of change of position. It is a vector physical quantity; both speed and direction are required to define it. In the SI (metric) system, it is measured in meters per second: (m/s) or ms 1. The scalar… … Wikipedia**Velocity obstacle**— The velocity obstacle VOAB for a robot A, with position xA, induced by another robot B, with position xB and velocity vB. In robotics and motion planning, a velocity obstacle, commonly abbreviated VO, is the set of all velocities of a robot … Wikipedia