Multiplying Vectors in 3D Plane: Angles Explained

  • Context: Undergrad 
  • Thread starter Thread starter andrewkg
  • Start date Start date
  • Tags Tags
    3d Plane Vectors
Click For Summary

Discussion Overview

The discussion revolves around the concept of multiplying vectors in a 3D plane, specifically focusing on the definition and calculation of angles between two vectors. Participants explore both conceptual and computational aspects of this topic.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant expresses confusion about how angles between two vectors in 3D are defined, particularly beyond the dot and cross product equations.
  • Another participant questions whether the confusion pertains to the definition of the angle or the method of finding it from vector components.
  • A participant asserts that the dot and cross products are the primary means of determining angles between vectors in 3D, emphasizing the impracticality of using a protractor.
  • One participant describes a conceptual approach to measuring angles by placing vectors tail to tail and suggests that the angle can be calculated using the dot product formula.
  • A later reply indicates that while the participant knows the angle is approximately 110 degrees, they seek clarification on how that angle is defined in 3D space.
  • Another participant reiterates the conceptual method of placing vectors tail to tail and notes that the two vectors will lie in a two-dimensional plane for angle measurement.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definition of angles between vectors in 3D, and multiple viewpoints regarding the conceptual and computational aspects remain present.

Contextual Notes

There are unresolved aspects regarding the definitions and calculations of angles, as well as the assumptions made about the dimensionality of the vectors involved.

andrewkg
Messages
86
Reaction score
0
OK so I am a bit confused. I am doing multiplication of vectors. I am a bit confused about the angles between two vectors. Let's say a(vect)=(3.0)i-(4.0)j; b(vect)=(2.0)j+(3.0)k in unit vector notation. Or generally how are angles between two vectors in 3d defined. Not just in terms of the dot or cross equ.
 
Physics news on Phys.org
It is not clear what your confusion is about.

Is it about the definition of the angle between two vectors?

Or is it about finding the angle between two vectors given their components?
 
AFAIK, dot and cross products are how angles between vectors are determined, esp. in 3D. It's not like you are going to slap a protractor on them and read off the angle.
 
Conceptually, the angle between two vectors is what you get if you put them together tail to tail and use a protractor to measure the angle that this forms. Calculationally, if you have the components of both vectors as in your example, equate the two common formulas for the dot product and solve for the angle:

$$A_x B_x + A_y B_y + A_z B_z = |\vec A||\vec B| \cos \theta$$
 
Never mind I misread something earlier. Making my question very illogical. Sorry. Thanks though.
 
Last edited:
andrewkg said:
I know how to find the angle between vectors. I know theta is ~110 just don't know where the ~110 deg comes from. By this I mean how is that angle defined. I just do not know how angle between vectors in a 3d plane are defined.

Conceptually, you put the two vectors together tail to tail as jtbell says above. The two vectors will lie in a single two-dimensional plane (which may be slanted/tilting); in that two-dimensional plane you can use a protractor to find the angle just as you would if you had started with vectors in only two dimensions.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 8 ·
Replies
8
Views
756
  • · Replies 2 ·
Replies
2
Views
1K
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 9 ·
Replies
9
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K