Torque = r x F

[Harmony]

I saw in my reference book that T=r * F , and T=F * r is unacceptable. Why is the latter unacceptable?

 

[mybsaccownt]

Torque = r x F

it is a cross product

and r x F is not the same as F x r

"The cross product is anticommutative,

a × b = −b × a "

http://en.wikipedia.org/wiki/Cross_product

 

[turdferguson]

Also, the book probably doesn't want you to confuse units of torque (meter*Newtons) and units of energy (Newton*meters). Get in the habit of putting the distance first, as it will help you with the cross products

 

[cristo]

Also, the book probably doesn't want you to confuse units of torque (meter*Newtons) and units of energy (Newton*meters).

Huh? The (standard) unit of torque is the Newton-metre; I've never heard of it being called a metre-Newton! Besides, clearly the units Newton and metre commute.

(http://en.wikipedia.org/wiki/Newton_metre)

 

[turdferguson]

If the unit of torque is the Newton-meter, that implies that its the same as a joule. By using the term "meter-Newton", you can easily differentiate between torque and energy. Even though you just informed me that its not technically SI, it makes more sense to me and probably to someone just starting out