# Homework Help: Ωxr vs rxω

1. Mar 30, 2012

### Icetray

Hi guys,

I just wanted to know when to use ωxr and when to use rxω when we're making vector based calculations. I realized that when reversed te calculations tend to differ a lot.

Thanks for the help in advance!

2. Mar 30, 2012

### QuarkCharmer

$$AxB = -BxA$$

It's strictly convention. The magnitude of the vector you get will be the same either way, however, it will be in the opposite direction. You need to think about the problem asked to figure out which way you should perform the cross product.

3. Mar 30, 2012

### Staff: Mentor

They result in a different direction for the resultant (diametrically opposite direction, actually). The cross product is a mathematical operation that is order dependent.

There is no way to answer your question without knowing the context; If a physical "law" is involved then the order is specified to result in the correct direction given that the vectors involved are specified in a standard "right handed" coordinate system.

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