High School Confused about dot product multiplication

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SUMMARY

The discussion centers on the concept of the dot product in vector mathematics, specifically how it measures the projection of one vector onto another. The dot product is defined as A · B = |A||B|cos(α), where α is the angle between the vectors. Participants clarify that the dot product quantifies how much one vector extends in the direction of another, with practical applications in physics, such as calculating work done by a force vector over a displacement vector. The value of the dot product can indicate the relative direction of the vectors, with maximum, minimum, and zero values corresponding to parallel, opposite, and perpendicular orientations, respectively.

PREREQUISITES
  • Understanding of vector operations, including addition and scaling.
  • Familiarity with trigonometric functions, particularly cosine.
  • Basic knowledge of physics concepts, such as force and work.
  • Ability to interpret geometric representations of vectors.
NEXT STEPS
  • Study the geometric interpretation of the dot product and its applications in physics.
  • Learn about vector projections and how they relate to the dot product.
  • Explore the relationship between the dot product and the cosine of the angle between vectors.
  • Investigate the use of dot products in higher-dimensional vector spaces.
USEFUL FOR

Students of mathematics and physics, educators teaching vector calculus, and professionals applying vector analysis in engineering or computer graphics will benefit from this discussion.

  • #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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