Can the magnitude of vector be negative?

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Discussion Overview

The discussion centers around the concept of vector magnitudes and whether they can be negative. Participants explore the definitions and distinctions between scalars, magnitudes, and absolute values in the context of vectors, including specific examples.

Discussion Character

  • Conceptual clarification, Debate/contested, Technical explanation

Main Points Raised

  • One participant questions if the magnitude of a vector can be negative, referencing the nature of scalars.
  • Another participant asserts that the magnitude of a vector is calculated using the formula sqrt(x1^2 + ... xn^2), implying it cannot be negative.
  • A participant distinguishes between "absolute value" and "magnitude," suggesting they are used in different contexts (numbers vs. vectors) but acknowledges that "absolute value of a vector" might not cause confusion.
  • Another participant states that the absolute value of a vector is referred to as the "norm."
  • It is noted that while the magnitude of a vector is always positive or zero, there exist scalars that can be negative, such as those arising from the scalar product of two vectors.

Areas of Agreement / Disagreement

Participants generally agree that the magnitude of a vector is always non-negative. However, there is some disagreement regarding the terminology and the relationship between scalars and vector magnitudes.

Contextual Notes

There is an unresolved distinction between the terms "absolute value" and "magnitude," as well as the implications of negative scalars in relation to vector magnitudes.

Red_CCF
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Recently I was told that scalars, although magnitude only, can be negative. Does this mean that the magnitude of a vector can be negative too?

Also, I'm wondering if there's a difference between the absolute value and magnitude of a vector like -3i-4j. Thanks for any help that you can provide
 
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no, the magnitude of a vector is computed by sqrt(x1^2 + ... xn^2)
 
Red_CCF said:
Also, I'm wondering if there's a difference between the absolute value and magnitude of a vector like -3i-4j. Thanks for any help that you can provide

I say "absolute value" only when I'm talking about a number, and "magnitude" when I'm talking about a vector. I don't know if it's actually incorrect to say "absolute value of a vector." Nevertheless, I don't think there's any chance you would confuse people by saying "absolute value of a vector," because I can't think of anything else besides the magnitude that it could be interpreted to mean.
 
the absolute value of a vector is the "norm"
 
The magnitude (a.k.a. norm or length) ǁaǁ of a vector a is a scalar and is always positive (or zero).

But there are scalars that are not magnitudes of vectors and they can be negative. (For example the scalar product (a.k.a. dot product or inner product) of two vectors a.b).
 

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