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The Cross Product

There is another way that two vectors can be multiplied. While the dot product of two vectors produces a scalar, the cross product of two vectors is a vector. As such, it has both magnitude and direction. The cross product of the vectors tex2html_wrap_inline585 and tex2html_wrap_inline521 is written as tex2html_wrap_inline793 and has a magnitude given by

equation322

where tex2html_wrap_inline721 is the angle between the two vectors.

The direction of the cross product is perpendicular to both of the vectors. To get the correct orientation, use the right-hand rule. Point your index finger (of your right hand) along the first vector. Then orient your hand so that your middle finger points along the second vector. Extend your thumb. It points in the direction of the cross product.

Notice that the greater the angular separation of the two vectors, the larger the cross product's magnitude.

When the angle between the vectors is greater than 180 degrees, the cross product flips over to point in the opposite direction.

Now let's calculate some simple cross products.

  1. tex2html_wrap_inline797 since the angle between the vectors is 0 and tex2html_wrap_inline799 .
  2. tex2html_wrap_inline801 since tex2html_wrap_inline803 , and tex2html_wrap_inline643 is perpendicular to both vectors. Check this with the right hand rule.
  3. tex2html_wrap_inline807 since the magnitude of both vectors is one, the angle between them is 90 and the right hand rule produces a result in the tex2html_wrap_inline809 direction.

Try calculating the cross product of the basis vectors in other combinations.





Vector Calculus
Mon Jul 14 10:10:30 MST 1997