What is Position vector: Definition and 110 Discussions

In geometry, a position or position vector, also known as location vector or radius vector, is a Euclidean vector that represents the position of a point P in space in relation to an arbitrary reference origin O. Usually denoted x, r, or s, it corresponds to the straight line segment from O to P.
In other words, it is the displacement or translation that maps the origin to P:





r

=



O
P






{\displaystyle \mathbf {r} ={\overrightarrow {OP}}}
The term "position vector" is used mostly in the fields of differential geometry, mechanics and occasionally vector calculus.
Frequently this is used in two-dimensional or three-dimensional space, but can be easily generalized to Euclidean spaces and affine spaces of any dimension.

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  1. O

    When gradient is parallel to position vector

    Homework Statement suppose that grad of f(x,y,z) is always parallel to the position vector xi+yj+zk. show that f(0,0,a)=f(0,0,-a) for any a. The Attempt at a Solution grad of f= fx(x,y,z)i+fy(x,y,z)j+fz(x,y,z)k ; then gradf (dot) pos.vector = |gradf|*|pos.vector| (since cos(teta)=1 )...
  2. B

    What Time to Turn Off the Spaceship Engine for Optimal Coasting?

    Homework Statement Suppose that the position function of a spaceship is r(t) = (3+t)i + (2+ln T)j + (7-4/t^2+1)k. Suppose you want the ship to coast to a space station located at (6.4.9). What time should you turn your engine off? Homework Equations r' = velocity. r" = acceleration...
  3. B

    Position Vector Problem

    Homework Statement The position function of a spaceship is r(t) = (3+t)i + (2+ln t)j + (7 - 4/(t^2+1)k and the coordinates of the space station are (6,4,9). If the spaceship were to "coast" into the space station, when should the engines be turned off? Homework Equations The...
  4. M

    Spherical coordinates position vector

    can anyone help me with this question: A sphere of unit radius is centered at the origin. points U,V & W on the surface of the sphere have vectors u,v & w. find the position vector of points P&Q on a diameter perp to the plane containing points U,V & W? can anyone help
  5. S

    Position Vector: Why Does it Always Point Radially Outward?

    I was wondering, why does the position vector always points radially out from the center (for example, in circular motion). I figure that this is because \vec{v} = \frac{d \vec{r}}{dt} and the velocity should always be tangent to the "curve" (because of Newton's first law). But is there any...
  6. D

    Integrated and got position vector

    3. A tennis ball is served horizontally from 2.4 m above the ground at 30m/sec a) Find its velocity (V) at any time t seconds b) Find its position vector (r) at any time t second a) v= 30i - gtj b) i integrated and got position vector as p= 30ti(2.4-.5gt^2)j is that it?
  7. U

    Position Vector of Center of Mass: What is dm?

    it is said that the posiion vector of the cener of mass of a rigid body can be obtained by: r_{CM}= \frac{1}{M} \int r dm I'm not sure I understand this expression. What exactly is dm? and I thought it was the sumation of mass times distance divided by the total mass...
  8. G

    Particle has position vector 2i + j

    A particle has position vector 2i + j (i is along x-axis and j is along y axis) initially. and is moving with speed of 10m/s in the direction 3i-4j. Find its position vector when t=3 and the distance it has travlled in those 3 seconds. Please help me with the first part of the question. :confused:
  9. Q

    Perpendicular position vector and velocity?

    I have been struggling with this question for a little while now and after drawing pictures and such I just cannot think of a situation in which this is possible. I was wondering if somebody with a little bit more physics knowledge could enlighten me :rolleyes: ? Here it is: "Describe a...
  10. C

    Partial Derivatives of Position Vector

    Let \vec{r} = \vec{r}(q_1,\ldots,q_n) . Is the following ALWAYS true? \frac{\partial \vec{r}}{\partial q_i} \cdot \frac{\partial \vec{r}}{\partial q_j} = \delta_{ij} Edit: Perhaps I should ask if it is zero when i \neq j rather than saying that it is 1 when i = j I guess...
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