High School Confused about dot product multiplication

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The discussion centers on the confusion surrounding the dot product of vectors and what it truly measures. Participants clarify that the dot product quantifies the projection of one vector onto another, represented mathematically as A · B = |A||B|cos(α), where α is the angle between the vectors. This operation effectively calculates how much one vector extends in the direction of another, which can be visualized as the length of one vector's "shadow" on the other. Examples, such as calculating work done by a force vector along a displacement vector, illustrate practical applications of the dot product. Ultimately, understanding the dot product requires recognizing its geometric interpretation and relevance in various mathematical and physical contexts.
  • #31
Given a gradient of a function, ##\vec \nabla f##, and a vector ##\vec v##, the dot product, ##\vec \nabla f \cdot \vec v##, is the directional derivative of ##f## in ##\vec v##.
 
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  • #32
Aurelius120 said:
I could be wrong. But don't all intuitive examples involving both physics and dot product that are also simple, involve forces?
You could be right. But presumably it depends upon what is classified as intuitive/simple.

For example Gauss's law is fairly intuituve/simple after studying basic electromagnetism. It involves the dot product of the electric field vector and the 'area vector'. (But in fact force is hidden in there - because the electric field vector depends on electric force.)

Edit: Aha. @PhDeezNutz beat me to it.
 
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  • #33
NoahsArk said:
I meant some kind of word problem example using a specific real world application to illustrate how the dot product works.
Suppose a company sells five different products, call them A, B, C, D, and E. Suppose also that during a month, there were, respectively 25, 30, 15, 20, and 40 units sold, with per-unit revenues of $100, $120, $85, $140, and $135.
If the number sold is ##\overrightarrow{N_{sold}} = <25, 30, 15, 20, 40>## and the per-unit revenue is ##\vec R = <100, 120, 85, 140, 135>##, then the total revenue is given by ##\overrightarrow{N_{sold}} \cdot \vec R##. The units of this number would be dollars.
 
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  • #34
NoahsArk said:
I meant some kind of word problem example using a specific real world application to illustrate how the dot product works.
There must be a parable that covers your situation. Mathematics is a mountain. You have to start climbing to make progress. You can only sit at the bottom looking up for so long. You must have made a decision at some point to attempt this mountain, so you ought to get on with it.
 
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