Homework Help: Cross products vs. dot products

1. Oct 15, 2011

Joyci116

I have a question regarding cross products and dot products. What is the difference, and are there any similarities? What ARE cross products and what are their functions? What ARE dot products and what are their functions? What do we use them for?

Thank you,

Joyci116

2. Oct 16, 2011

paul2211

Well, first of all, you use cross products and dot products when you work with vectors, and I would say (at least how I convinced myself) they are something made up by mathematicians to make vectors useful.

A cross product between two vectors products another vector that is orthogonal to the original two. For example, cross product can be used to find the moment:

M = r x F

A dot product, on the other hand, between two vectors produces a scalar, basically a number. Dot product can be used to calculate the work done by a force:

W = F d

P.S. The bold letters are vectors, and the unbold ones are scalar.

3. Oct 16, 2011

Joyci116

So what you are trying to convey is that you multiply with cross products and dot products, but it is WHAT you multiply determines whether it is a dot or cross product? Scalar is always dot and vector is always cross product?