Scaling Vectors in Problems: What, When & Why?

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    Scaling Vectors
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Discussion Overview

The discussion revolves around the conditions under which vectors should be scaled in various problems, particularly in the context of finding unit vectors and their applications in physics and mathematics. Participants explore the implications of scaling vectors, especially in relation to perpendicularity and distance measurements.

Discussion Character

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

Main Points Raised

  • Some participants question when scaling vectors is necessary, particularly in problems involving unit vectors and perpendicularity.
  • It is noted that a unit vector has a magnitude of 1, and participants discuss the implications of this definition in relation to the cross product of two vectors.
  • Some argue that while the cross product of two vectors is always perpendicular to both, it does not qualify as a unit vector unless scaled.
  • There is a discussion about the geometric differences between scaled and unscaled vectors, with some suggesting that scaling affects the length but not the direction.
  • Participants explore the idea that using unit vectors can simplify distance calculations, akin to using a standard measuring stick.
  • Some express uncertainty about whether unscaled vectors can still be valid in distance problems, seeking clarification on their applicability.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity of scaling vectors in all scenarios, with some asserting that unscaled vectors can still be used effectively while others emphasize the importance of scaling for unit vectors.

Contextual Notes

Participants highlight that the need for scaling may depend on the specific problem context, such as whether a unit vector is explicitly required or if the problem involves distance measurements.

mill
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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 problems?

Furthermore, for this problem

A unit vector that is perpendicular to both v = <1; 3; 2> and w = <4; 2; 1> is...

I thought would be vxw, but the answer is (1/(5sqrt(6))vxw. Why was scaling needed here?
 
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"A unit vector" means a vector whose magnitude is equal to 1.

Does the vector v x w from your example have a magnitude equal to 1?
 
SteamKing said:
"A unit vector" means a vector whose magnitude is equal to 1.

Does the vector v x w from your example have a magnitude equal to 1?

No. Does this mean that I would need to scale everything not equal to 1? How is simply v x w different from the scaled v x w in finding the vector perpendicular to both?
 
You are asked to find a unit vector. When you are asked to find a unit vector, you have to scale your vector to have magnitude 1. If you are not asked to find a unit vector, you can leave the vector as is. The difference in vectors is just scaling...
 
Matterwave said:
You are asked to find a unit vector. When you are asked to find a unit vector, you have to scale your vector to have magnitude 1. If you are not asked to find a unit vector, you can leave the vector as is. The difference in vectors is just scaling...

I see. But for that problem, even if unscaled, wouldn't v x w still be perpendicular to v and w? I guess I don't see how the scaled answer is the only correct one.
 
mill said:
I see. But for that problem, even if unscaled, wouldn't v x w still be perpendicular to v and w? I guess I don't see how the scaled answer is the only correct one.

Yes, v x w is always perpendicular to both v and w. You are asked SPECIFICALLY to find the UNIT vector that is perpendicular to both v and w. The only one (actually 2 since there's one going the other way) is the scaled version. Unscaled versions are not UNIT vectors, but they are still perpendicular.
 
Matterwave said:
Yes, v x w is always perpendicular to both v and w. You are asked SPECIFICALLY to find the UNIT vector that is perpendicular to both v and w. The only one (actually 2 since there's one going the other way) is the scaled version. Unscaled versions are not UNIT vectors, but they are still perpendicular.

I see.

How do scaled vectors function differently from simply vectors in problems (geometrically)? In what type of problems must scaling take place? Typically, distance problems? Other than the bug walking problem I've only seen it used with the helicopter flying in a certain direction. Do vectors need to be scaled in cases of finding distance away from a curve?
 
The scaled vectors are just shorter or longer than the unscaled vectors...there's no other difference.

It's good to use unit vectors because then your distances will come out in good units. This is like using a meter stick that is exactly 1 meter long. You are certainly free to use a meter stick that is 1.43 meters long, but all your measurements come out in multiples of 1.43 meters...
 
Matterwave said:
The scaled vectors are just shorter or longer than the unscaled vectors...there's no other difference.

It's good to use unit vectors because then your distances will come out in good units. This is like using a meter stick that is exactly 1 meter long. You are certainly free to use a meter stick that is 1.43 meters long, but all your measurements come out in multiples of 1.43 meters...

Thanks. I think I got it. Just to clarify, it is still correct to use unscaled vectors in distance problems?
 
  • #10
You can use whatever you want, as long as you make sure you know what you're doing, so you can give the correct answer in the end.

Just as the meter stick analogy. You are free to use a 1.43 meter long meter stick, as long as you know in the end to give your results in the correct way. So if something is 2 times as long as your 1.43 meter long meter stick, know that this thing is 2.86 meters long and NOT 2 meters long.
 
  • #11
Got it. Thanks.
 

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