Vector Subtraction: S-T Magnitude Explained

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Discussion Overview

The discussion revolves around understanding vector subtraction, specifically the calculation of the magnitude of the difference between two vectors, S and T, with given magnitudes of 3 m and 4 m respectively. Participants explore various scenarios and interpretations related to the subtraction of these vectors, including their directions and the implications for the resulting magnitudes.

Discussion Character

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

Main Points Raised

  • One participant expresses difficulty in understanding vector subtraction and references a problem from a book that presents three different magnitudes for the difference S - T: 7 m, 5 m, and 1 m.
  • Another participant notes that vectors S and T must have directions, questioning whether these directions are provided.
  • A subsequent post clarifies that the vectors are depicted with arrows pointing in the same direction, but T is considered negative.
  • There is a discussion about the implications of subtracting T from S, with one participant suggesting that subtracting implies changing the direction of T.
  • A participant proposes that the scenario could involve different configurations of the vectors, such as both pointing in the same direction or at right angles, affecting the resultant magnitude.
  • One participant encourages others to visualize the resultant vector through sketches and hints at using the Pythagorean Theorem for perpendicular vectors.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct interpretation of the problem or the resulting magnitudes from the vector subtraction. Multiple competing views regarding the directions and configurations of the vectors remain present.

Contextual Notes

Limitations include the lack of specific directional information for vectors S and T, which affects the understanding of their subtraction. The discussion also highlights the need for clearer problem descriptions or visual aids to facilitate comprehension.

savageqm
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This is my first time leaning physics and the vectors are really hard to understand so far(doesn't help that the teacher has not taught it in depth)

am reading the book and they have a sample problem that states:
S=3 m and T=4 m

The question is what is the magnitude of the difference vectors S - T.

The books shows three answers which is; 7m, 5m and 1m

please explain me how they came up with these answers.

7m I think I understand because they added 3 + (-4), but the rest am lost.
 
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If S and T are vectors, they must have a direction. Are they given?
 
well that books just shows them with the arrows on top pointing the same way but T is negative.
 
If the arrows are pointing in the same direction, then to add them, you just get 7m pointing in the same direction as the original vectors. But what if you subtract T from S...then what do you get

Edit: are these 3 different questions or one multiple choice question. A picture might help or a better description. When you subtract vectors, S and T, then S - T = S + (-T). The minus in front of the T implies that you change the direction of T so its pointing in the opposite direction.
 
Last edited:
maybe this will help.
http://cid-3c099006138591f8.photos.live.com/self.aspx/Public/DSCN7108.JPG"
 
Last edited by a moderator:
OK, you have 2 vectors, S and T, which you can point in any direction you choose, and now you want to calculate S - T, for different directions of those vectors. The magnitude of S is 3, and the magnitude of T is 4. You seem to have found one solution, when the S vector is 3 units to the right, and the T vector is 4 units to the left, then their vector difference (S - T) is 7 units to the right, and the magnitude of that result is 7. But what if the S vector is 3 units to the right, and the T vector is 4 units to the right. What's the magnitude of the vector difference then? And what if S and T are at right angles (perpendicular) to each other? Then you'll have to find the magnitude of the resultant difference by using the Pythagorean Theorem ( are you familiar with that ? Hint..what's the diagonal measure?).

Now play around with graphing the resultant vector for different directions, using rough sketches. The resultant can never be bigger than a certain number, nor less than another certain number.
 

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