What is Vectors: Definition and 1000 Discussions

In mathematics, physics and engineering, a Euclidean vector or simply a vector (sometimes called a geometric vector or spatial vector) is a geometric object that has magnitude (or length) and direction. Vectors can be added to other vectors according to vector algebra. A Euclidean vector is frequently represented by a ray (a directed line segment), or graphically as an arrow connecting an initial point A with a terminal point B, and denoted by






A
B






{\displaystyle {\overrightarrow {AB}}}
.A vector is what is needed to "carry" the point A to the point B; the Latin word vector means "carrier". It was first used by 18th century astronomers investigating planetary revolution around the Sun. The magnitude of the vector is the distance between the two points, and the direction refers to the direction of displacement from A to B. Many algebraic operations on real numbers such as addition, subtraction, multiplication, and negation have close analogues for vectors, operations which obey the familiar algebraic laws of commutativity, associativity, and distributivity. These operations and associated laws qualify Euclidean vectors as an example of the more generalized concept of vectors defined simply as elements of a vector space.
Vectors play an important role in physics: the velocity and acceleration of a moving object and the forces acting on it can all be described with vectors. Many other physical quantities can be usefully thought of as vectors. Although most of them do not represent distances (except, for example, position or displacement), their magnitude and direction can still be represented by the length and direction of an arrow. The mathematical representation of a physical vector depends on the coordinate system used to describe it. Other vector-like objects that describe physical quantities and transform in a similar way under changes of the coordinate system include pseudovectors and tensors.

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  1. Dany

    Master Linear Algebra: A Beginner's Guide to Vectors for Physics Students

    Hi everybody, I'm a physics student and this is my first post here and i will begin asking one favor: Anyone could recommend a simple and accessible book about vectors in linear algebra?? I'm already read several books and didn't understand anything.. :cry: I really need to recover my...
  2. L

    Calculating Torque with Vectors at an Angle

    Homework Statement So I was wondering how do we account for vectors that are at a certain angle. The problem that I'm having with the picture is: if I was calculating torque from point B, how would I account for the vector G. Homework Equations The Attempt at a Solution I've...
  3. S

    Force vectors acted on by two forces

    Homework Statement A body is acted on by two forces. Find the magnitude and direction of the resultant force by using the mathematical method. I'm not sure if I've done this correctly, any pointers would be appreciated :) Also what is the angle between the two vectors? Is it 90 or 76 degrees...
  4. A

    Cross and dot product of two vectors in non-orthogonal coordinate

    Hi everyone, I have to find out how to do cross and dot product for two vectors in non-orthogonal coordinate system. thanks
  5. J

    Vectors and discrete time signals

    How can a discrete time signal can be a vector? i cannot grasp the idea. i know MATLAB uses matrices which denote vectors, but how does a discrete time varying amplitudes be a vector?
  6. M

    Why must the form of v_i v_j be independent of coordinate system?

    Hey PF! I am trying to understand what is meant when we say a vector is invariant, which I believe is independent of a coordinate system. I have already read a PF post here: https://www.physicsforums.com/showthread.php?t=651863. I'm looking at DH's post, and this makes a lot of sense...
  7. kq6up

    Inner Product of Complex Vectors?

    I was reading in my textbook that the scalar product of two complex vectors is also complex (I assuming this is true in general, but not in every case). However for the general definition (the inner product), each element of one of the vectors needs to be its complex conjugate. I learned this...
  8. J

    What is the relationship between two vectors in terms of rotation and scaling?

    I want find a value M such that given v and u, satisfies the equation v=Mu. Well, the vector u has a modulus u and a direction α wrt x-axis; the vector v has another modulus v and another direction β wrt x-axis. What is happened is a change of magnitude and direction of the vector u...
  9. D

    How Do You Calculate the Angle Between Two Vectors?

    Hi Guys, Im working on finding an angle between two vectors. a [ 1,2,3 ] b [ 4, -1, 0] //a// = sqrt(1^2+2^2+3^2) = sqrt14 //b// = sqrt(4^2+(-1)^2+0^2 = sqrt17 Dot product 1.4 + 2.-1 + 3.0 = 2 cos^-1 2/ sqrt14 sqrt17 cos^-1 (1/( ? ) Thanks
  10. M

    Deriving Photon Rotation Formula for Monte Carlo Simulation - Step-by-Step Guide

    Hello and apologies if the title of the question is not very precise. Question: I am reading the document talking about the simulation of photons in tissues using a Monte Carlo simulation. The exact title is "MCNP - A general Monte Carlo N-Partcle Transport Code". Link to MCNP - A general...
  11. M

    Relation between unit tangent/normal vectors, curvature, and Lin. Alg.

    Hey there, This isn't a homework question, it's for deeper understanding. So I'm learning about unit normal/tangent vectors and the curvature of a curve. I have a few questions/points. 1) So my book states that we can express acceleration as a linear combination of the acceleration in the...
  12. kq6up

    State vectors and Eigenvalues?

    If I define a state ket in the traditional way, Say: $$|\Psi \rangle =\sum _{ i }^{ }{ a_{ i }|\varphi _{ i }\rangle \quad } $$ Where $$a_i$$ is the probability amplitude. How does: $$\hat {H } |\Psi \rangle =E|\Psi \rangle $$ if the states of $$\Psi$$ could possibly represent states...
  13. E

    How Do You Solve Vector Problems in Physics?

    I am having trouble solving a basic problem in the use of vectors. The problem comes from Alonso & Finn "Fundamental University Physics" Volume 1, Chapter 3 Problem 12 and states "The pennant on the masthead of a sailboat streams back at an angle of 45 degrees (South of West), but the flag on...
  14. M

    Given vectors how to find third equation

    Homework Statement If |v|=4, |w|=3 and the angle between and is pi/3, find |2v −w| Homework Equations ##cosθ=\frac {v dot w} {|v||w|} ##The Attempt at a Solution ## 6= v dot w ## This is as far as I got. How would I find the separate values of v and w for the equation?
  15. M

    Scaling Vectors in Problems: What, When & Why?

    I've made mistakes where scaling was used but I just assumed that I didn't need it. e.g. a bug walking towards <1,1,1> is scaled to <1/sqrt(3), etc>. Under what kind of conditions/in what kind of problems should vectors be scaled? I know that v/|v| is the unit vector but how do I relate this to...
  16. N

    Set of vectors whose coordinates are integer (is a subspace?)

    Homework Statement For a set of vectors in R3, is the set of vectors all of whose coordinates are integers a subspace?The Attempt at a Solution I do not exactly understand if I should be looking for a violation or a universal proof. If x,y, z \in Z then x,y,z can be writted as...
  17. Joffan

    Sum of arbitrary vertex to midpoint vectors

    I was looking at a homework question posted here requiring proof that the vectors from the vertices of a triangle to the midpoint of the opposite edge sum to zero, and it struck me that there is a more general property: Consider a set of points, \{A_0, A_1, \ldots A_n\}. The midpoint of...
  18. S

    Area of a Triangle Using Vectors.

    Homework Statement A triangle has verticies A(-2,1,3), B(7,8,-4), and C(5,0,2). Determine the area of the triange ABC. The correct answer is 35.9 square units. Homework Equations Has to be done by using dot product and/or cross product. Dot product: a(dot) b= |a||b|cos(theta) Cross...
  19. L

    Vectors with a dose of arithmetic :3

    Homework Statement Two velocities acting at a particular point are such that: The sum of their respective magnitudes is 15m/s The product of their respective magnitudes are 56m2/s2 The resultant is 13m/s. Find the two velocities and the angle between them. Homework Equations R^2 = P^2 + Q^2...
  20. J

    Show that a line does not intersect a plane (vectors)

    Homework Statement A plane is given by the equation: 4x + 5y + 7z = 21 and a line by the equation r = (1,2,3) + \lambda (1,2,-2) where λ is real. Show that the line does not intersect the plane. The attempt at a solution So if I remember correctly, if n . a = 0 , they do not...
  21. P

    Define Tetrahedron knowing one vertex, 3 vectors, opposite face.

    I have a unique problem that I'm struggling with with regards to surveying. Because my surveying equipment is much more accurate at measuring angles than distances I'd like to find an analytic solution using only the angular measurements. Let the surveyor sit at the origin of the...
  22. J

    Two linearly independent vectors in a plane that don't span the plane

    Homework Statement Say we have the plane, x+2y+4z=8 (part of a larger problem) Homework Equations The Attempt at a Solution The vectors (8,0,0) and (0,0,2) both lie in the plane. They are linearly independent. But (0,4,0) lies in the plane and is not a linear combination of the first two...
  23. H

    How Does Force Angle Affect Book Acceleration with Friction?

    Homework Statement A book of mass M = .55 kg rests on a table where the coefficient of static friction us = .45. A force, F = 4 N acts on the book at an angle of 15 degrees above the surface of the table. What is the acceleration of the book if the coefficient of kinetic friction uk = .23...
  24. N

    Derivatives of contravariant and covariant vectors

    Can someone explain why the derivative with respect to a contravariant coordinate transforms as a covariant 4-vector and the derivative with respect to a covariant coordinate transforms as a contravariant 4-vector.
  25. nomadreid

    Confusion about basis vectors and matrix tensor

    In "A Student's Guide to Vectors and Tensors" by Daniel Fleisch, I read that the covariant metric tensor gij=ei°ei (I'm leaving out the → s above the e's) where ei and ei are coordinate basis vectors and ° denotes the inner product, and similarly for the contravariant metric tensor using dual...
  26. M

    Example about tangential and normal unit vectors

    Here is a example 1.3 from analytical dynamics of Haim Baruh. a particle moves on a path on the xy plane defined by the curve y=3*x^2 , where x varies with the relation x= sin(a). find the radius of curvature of the path and unit vectors in the normal and tangential directions when a=pi/6...
  27. kq6up

    How do you use vectors to prove the theorem about parallelogram diagonals?

    Homework Statement This problem is from Mary Boas' "Mathematical Methods in the Physical Sciences" 3rd Ed. Capter 3 Section 4 Problem 3 Use vectors to prove the the following theorems from geometry: 3. The diagonals of a parallelogram bisect each other. Homework Equations Just...
  28. N

    Help required w/ vectors: general equations, intersection points

    Homework Statement In this question we consider the following six points in R3: A(0,10,3) B(4,18,5) C(1,1,1) D(1,0,1) E(0,1,3) F(2,6,2) a) Find a vector equation for the line through the points A and b b) Find general equations for the line from a c) Find a vector equation for the...
  29. G

    Calculating Vector Sum: 40 ft and 14 degrees south of west - Vectors J and K

    Homework Statement Vector J has a magnitude of 28 ft and a direction of 34 degrees west of north. Vector K has a magnitude of 48 ft and a direction of 20 degrees south of east. Find the magnitude and direction of their sum. a) 30 ft and 13 degrees north of east b) 36 ft and 54 degrees...
  30. O

    Vectors - dot product and cross product?

    Vectors -- dot product and cross product? Hello may i know when to dot product and cross product?? both look to same to me..
  31. A

    Vector Ratios: Solving for Unknowns | Homework Help

    Homework Statement question attached Homework Equations The Attempt at a Solution i can't understand III i can't understand what he wants , if he wants the ratio , the ratio between AP and PB was 3/5 which is not the same as OA and OB (λ=3/8)
  32. J

    Vector Derivatives Explained: Definition and Examples

    What means: ? This guy, ##\vec{\nabla}_{\hat{\phi}} \hat{r}##, for example, means: \\ \hat{\phi}\cdot\vec{\nabla}\hat{r} = \begin{bmatrix} \phi _1 \\ \phi _2 \\ \end{bmatrix} \begin{bmatrix} \frac{\partial r_1}{\partial x} & \frac{\partial r_1}{\partial y} \\ \frac{\partial...
  33. C

    Solving for a variable in an equation that involves vectors

    Homework Statement I have the equation: \mathbf{F}_{2,1} = \frac{Q_1 Q_2}{4 \pi \varepsilon_0 {r_{2,1}}^2}\hat{r}_{2,1} (standard electric force equation for 2 charges) I know the value of everything except Q2 and have to find it. The vectors each have 3 components. Normally in an...
  34. L

    Linear independancy and orthogonality of vectors

    Hi, I'm reading up on linear algebra and I'm wondering if the remark after a theorem I'm reading here is complete. The theorem states: "If {V_1,V_2,...,V_k} is an orthogonal set of nonzero vectors then these vectors are linearly independent." Remark after that simply states that if a set of...
  35. F

    Integration including unit vectors

    I have an integral of aΘ cos(Θ) dΘ a is the unit vector for Θ. I'm not sure what to do with it in the integration. I know the unit vector equals a/abs(a) but that would give a mess of an integral cause of the abs(a).
  36. B

    Summation Convention for 2 Vectors

    From an exercise set on the summation convention: X and Y are given as [Xi] = \begin{pmatrix} 1\\ 0\\ 0\\ 1\end{pmatrix} and [Yi] = \begin{pmatrix} 0\\ 1\\ 1\\ 1\end{pmatrix} There are a few questions involving these vectors. The one I am stuck on asks to compute XiYj . It may be necessary...
  37. P

    Problem with drawing velocity vectors

    Homework Statement Hi all , I have a problem statement , I know how to solve it but I don't know how to graph velocities so I can use cartesian coordinate and thus have correct answers. Would you please help me ?? A pitcher throws a fastball, which crosses the plate with a speed of 95 mph...
  38. nomadreid

    States are or aren't unit vectors?

    I am a little confused by an elementary point. Something must be wrong with the following: On one hand, a Hermitian operator (which is not necessarily unitary) takes one state to another state. Hence a state need not be represented as a unit vector; its norm can be greater (or less than)...
  39. J

    Genaral PDE for scalar and vectors

    I realized that a PDE of 2nd order can written like: A:Hf+\vec{b}\cdot\vec{\nabla}f+cf=0 \begin{bmatrix} a_{11} & a_{12}\\ a_{21} & a_{22}\\ \end{bmatrix}:\begin{bmatrix} \partial_{xx} & \partial_{xy}\\ \partial_{yx} & \partial_{yy}\\ \end{bmatrix}f+\begin{bmatrix} b_1\\ b_2\\...
  40. N

    So, the title is: Parallel Vectors: Is AP Parallel to u?

    Mod note: Corrected a typo in the problem statement. Homework Statement IfIs the vector AP parallel to u? u= (1,4,-3) A(-2,-1,-2) The Attempt at a Solution I do know that if AP is parallel to u then there must be some scalar multiple such that Ax = u. I think it's a matter...
  41. T

    What is the distribution of the sum of two random vectors?

    I am trying to derive the distribution for the sum of two random vectors, such that: \begin{align} X &= L_1 \cos \Theta_1 + L_2 \cos \Theta_2 \\ Y &= L_1 \sin \Theta_1 + L_2 \sin \Theta_2 \end{align} With: \begin{align} L_1 &\sim \mathcal{U}(0,m_1) \\ L_2 &\sim...
  42. J

    Multiplication/division of matrices and vectors

    1) Let A a square matrix, x a colum vector and b another colum vector. So, I want solve for x the following equation: Ax=b So: x=b÷A = b×A-1 And this is the answer! Or would be this the correct answer x = A-1×b ? 2) Is possible to solve the equation above for A ? How?
  43. N

    Can an Alien See Earth and Venus at the Same Time? | Vectors and Angles Homework

    Homework Statement From an alien spaceship Earth is in the direction (1, -8, -4) and Venus is in the direction (3, 12, 4). The average alien eye has a field of view of 5pi/6 radians. Without using arccos or calculating any exact angles, determine if the average one eyed alien on the spaceship...
  44. C

    Solving for Orthogonal Vectors in R4?

    Homework Statement Given following vectors in R4: v= (4,-9,-6,3) u = (5,-8,k,4) w=(s,-5,4,t) A. Find value of k if u and v are orthogonal B. Find values of S and T if w and u are orthogonal and w and v are orthogonal Homework Equations Orthogonal means dot product is zero...
  45. M

    Electron Motion in Charged Plate Region: Time, Distance, and Velocity Components

    Homework Statement An electron, with an initial horizontal velocity of magnitude 3.16 × 109 cm/s, travels into the region between two horizontal metal plates that are electrically charged. In that region, it travels a horizontal distance of 2.42 cm and has a constant downward acceleration of...
  46. N

    Nullspace of Orthogonal Vectors: Example Matrix

    Homework Statement Let S be the subspace of all vectors in R4 that are orthogonal to each of the vectors (0, 4, 4, 2), (3, 4, -2, -4) What is an example of a matrix for which S is the nullspace? The Attempt at a Solution I'm not sure how I should be intepreting the question: [ 0 ,4 ,4 ,2...
  47. JasonHathaway

    Unit vectors in different coordinates

    Hi everyone, I've some points I want to make sure of. 1- When converting a "POINT" from a coordinate system to another, I'll just use the derived equation to convert (e.g. (1,2,3) from cartestian to cylindrical: \rho=\sqrt{x^{2}+y^{2}}, \phi=tan^{-1}\frac{y}{x}, z=z 2- When converting an...
  48. C

    How Do You Solve a Plane Equation in R^4 and Find Its Normalized Normal?

    Homework Statement Find equation of plan H in R^4 that contains the point P= (2,-1,10,6) and is parallel to plain H2: 4a +4b + 5c-6d = 3 then answer the following questions: A. find normalized normal of plane H which has an angle theta with the normal n= (4,4,5,-6) of H2 such that...
  49. P

    MHB Area between two vectors in R^n

    Hi, I wondered whether a well known expression is known that computes the area between two vectors in R^n. By area between two vectors, I mean the area that would be computed by considering the subspace spanned by the two, projecting the entire space to a "parallel plane" and then finally given...
  50. N

    Checking for linear independence of certain vectors

    Homework Statement Given that { u1, u2, u3, u4, u5, u6 } are linearly independent vectors in R16, and that w is a vector in R16 such that w ∉ span{ u1, u2, u3, u4, u5, u6 }. a) Is the set { 0, u1, u5 } is linearly independent? b) the set { u1, u2, u3, u4, u5, u6, w } is linearly...
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