Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Confusion between products

  1. Apr 10, 2004 #1
    i was taught in my physics lecture that Work =Force *distance *cos(A)
    to my belief this is the dot produict and used to measure area.
    in my maths lecture two vectors using the cross product is also used to find the area ie: N x M = N*M*sin(A)
    i thought that one product was used for area and the other for a different use along the lines of the projection of one vector upon another?
  2. jcsd
  3. Apr 11, 2004 #2
    You are correct that this is the dot product, but it is not used to measure area. The geometric meaning of the product of X-dot-Y is the length of the projection of vector X on the vector Y. Try drawing it for a better understanding.

    I don't know the geometric meaning of the cross product, but one property is that the resulting vector is always perpendicular to both original vectors. So for example, when dealing with surfaces you can find the normal vector by cross-product-ing two independent vectors on the surface itself.
  4. Apr 11, 2004 #3
    The dot product is not used to find area. As Chen said, it is the length of the projection.

    The magnitude of the cross product is the area of a parallelogram described by the two vectors.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook