radians are dimensionless, it follows that torque and energy have the same dimensions. The use of newton-metres for torque and joules for energy is useful in helping avoid misunderstandings and miscommunications. [ 5 ] An additional solution is to realize that joules are scalars – they are the dot product of a vector force and a vector displacement whereas torque is a vector. Torque is the cross product of a distance vector and a force vector. Drawing a traditional vector arrow over "newton-metre" in a torque resolves the ambiguity. The petajoule (PJ) is equal to one quadrillion (10 15 ) joules. 210 PJ is equivalent to about 50 megatons of TNT. This is the amount of energy released by the Tsar Bomba , the largest man-made nuclear explosion ever. ^ a b From the official SI website : "A derived unit can often be expressed in different ways by combining base units with derived units having special names. Joule, for example, may formally be written newton metre, or kilogram metre squared per second squared. This, however, is an algebraic freedom to be governed by common sense physical considerations; in a given situation some forms may be more helpful than others. In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension." ^ This is called the basal metabolic rate . It corresponds to about 5,000 kJ (1,200 kcal) per