When you use cross product and dot product in vector?

Answer 1

Dot product and cross product are used in many cases in physics. Here are some examples:

• Work is sometimes defined as force times distance. However, if the force is not applied in the direction of the movement, the dot product should be used. Note that here - as well as in other cases where the dot product is used - the product is greatest when the angle is zero; also, the result is a scalar, not a vector.
• The cross product is used to define torque (distance from the axis of rotation, times force). In this case, the product is greatest when the two vectors are at right angles. Also - as in any cross product - the result is also a vector.
• Several interactions between electricity and magnetism are defined as cross products.