I saw in my reference book that T=r * F , and T=F * r is unacceptable. Why is the latter unacceptable?
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.Also, the book probably doesnt want you to confuse units of torque (meter*newtons) and units of energy (newton*meters).