Geometrical meaning of magnitude of vector product

Click For Summary

Discussion Overview

The discussion revolves around the geometrical interpretation of the magnitude of the vector product, specifically $$|\vec v \times \vec w|$$. Participants explore its relationship to the area of a parallelogram formed by two vectors and the concept of perpendicular distance from a point to a line, examining whether these interpretations are consistent or if additional factors must be considered.

Discussion Character

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

Main Points Raised

  • One participant notes that the geometrical meaning of $$|\vec v \times \vec w|$$ is the perpendicular distance from point ##V## to line ##OW##, suggesting that the formula includes an additional factor of $$|\vec w|$$ that complicates this interpretation.
  • Another participant asserts that the magnitude of the cross product is the area of the parallelogram formed by the two vectors, relating it to the height and the magnitude of one of the vectors.
  • There is a question about whether it is correct to refer to the perpendicular distance from a point to a line as a standalone geometrical meaning without acknowledging the multiplication by the magnitude of the line.
  • One participant agrees with the concern raised about the interpretation of the perpendicular distance, indicating that the initial notes may have overlooked important details.
  • Further contributions reiterate that the magnitude of the cross product represents the area of the parallelogram, while also noting the dimensionality of the cross product as a (pseudo)vector.
  • A suggestion is made to use a unit vector along the line ##OW## to clarify the role of the length of segment ##OW## in calculating the distance from the line to point ##V##.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the geometrical meaning of the magnitude of the vector product, particularly regarding the relationship between perpendicular distance and area. There is no consensus on whether the perpendicular distance can be considered independently of the magnitude of the line.

Contextual Notes

Participants highlight the need for clarity regarding the assumptions involved in defining geometrical meanings, particularly the dependence on vector magnitudes and the context of the calculations.

songoku
Messages
2,509
Reaction score
393
TL;DR
I have notes that tells me one of the geometrical meaning of magnitude of vector product is related to perpendicular distance. Please see the diagram below
1629344653128.png


My notes says that the geometrical meaning of $$|\vec v \times \vec w | $$ is the perpendicular distance from point ##V## to line passing through ##O## and ##W## (all vectors are position vectors)

$$|\vec v \times \vec w | = |\vec v| |\vec w| \sin \theta$$

From the picture, the perpendicular distance is ##|\vec v| \sin \theta ## but from the equation, there is extra ##|\vec w|## so it seems to me that the geometrical meaning is not the perpendicular distance but more like the multiplication of perpendicular distance from point ##V## to line ##OW## and magnitude of ##\vec{OW}##

Am I misunderstood something?

Thanks
 
Physics news on Phys.org
The magnitude of v x w is the area of the parallelogram. It's "related to" the height in the sense that the area is the height multiplied by |w|.
 
  • Like
Likes   Reactions: songoku
mfb said:
The magnitude of v x w is the area of the parallelogram. It's "related to" the height in the sense that the area is the height multiplied by |w|.
I understand the other geometrical meaning is area of parallelogram but is it correct to say that one of the geometrical meaning is (only) perpendicular distance from a point to a line (without stating there is multiplication with magnitude of the line) ?

Because if I am asked to find perpendicular distance from ##V## to line ##OW##, I would calculate ##|\vec v| \sin \theta##, not ##|\vec v| |\vec w| \sin \theta##

Thanks
 
songoku said:
more like the multiplication of perpendicular distance from point ##V## to line ##OW## and magnitude of ##\vec{OW}##

Am I misunderstood something?
You are correct. Your notes must have missed something.
 
  • Like
Likes   Reactions: songoku
Thank you very much mfb and FactChecker
 
So the magnitude of the cross product is the area of the parallelogram with the two vectors as adjacent sides.
 
  • Like
Likes   Reactions: songoku
FactChecker said:
So the magnitude of the cross product is the area of the parallelogram with the two vectors as adjacent sides.
And what is interesting: the cross product is a (pseudo)vector and its magnitude should be of dimension L but not L^2 as it is so for the area :)
 
  • #10
songoku said:
I understand the other geometrical meaning is area of parallelogram but is it correct to say that one of the geometrical meaning is (only) perpendicular distance from a point to a line (without stating there is multiplication with magnitude of the line) ?

Because if I am asked to find perpendicular distance from ##V## to line ##OW##, I would calculate ##|\vec v| \sin \theta##, not ##|\vec v| |\vec w| \sin \theta##

Thanks
Use the unit vector \hat w along the line ##OW##.
(Indeed, what role would the length of the segment ##OW## play
to find the distance from that line to point ##V##?)
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 42 ·
2
Replies
42
Views
5K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K