![]() ![]() So, 1 Newton is the amount of Force required to increase the velocity of 1 Kg of point mass by 1 m/sec in 1 sec, in the direction of the change in velocity. There are 2 types of units viz., the basic/elementary units for mass, distance and time and the compound/derived units such Newton, Joule, etc for physical phenomenon that are derived from the basic units. So, the reason you can't use Joules for torque is because there is no consistent way of converting Newton-meters to Joules and vice versa. Units are defined for "magnitude of a vector", which by itself is a scalar. However, that can't be "the (only) reason" for different units. Someone pointed out that Torque is a vector (defined as a cross product) while Work is a scalar (defined as a dot product). The important thing is that there should be a consistent way to convert one unit to another. distance is generally measured in meters but it is also measured in light years which is the distance traveled by light in a year. It is not uncommon for units of a different physical entity to be used to measure a related physical entity. ![]() (Well, I suppose torque and energy are connected in various ways, just as any two randomly-selected quantities in classical mechanics are connected in various ways.) Torque and energy are completely different concepts that just happen to have algebraically-identical units. The fact that torque and energy have algebraically identical units does not mean torque and energy are the same in fact, it means nothing whatsoever. Therefore, having these different terms helps reduce the frequency of communication mistakes (albeit only to a limited extent). If I mumble something and point and say "50 newton meters", you can be pretty sure I'm talking about a torque if I say "50 joules" you can be pretty sure I'm talking about an energy. Why do people use different names for the same unit? Just the simple reason: It facilitates communication and avoids misunderstandings. In Gaussian units there is a delightful example of five algebraically identical units. Hertz is a unit of frequency, becquerel is a unit of frequency in the context of radioactivity. ![]() This is not the only example: Ohms is a unit of resistance, while "ohms per square" is an algebraically identical unit of sheet resistance. Joule and Newton meter are two units that are algebraically identical you might say they are two names for the same unit. Per the knowledge of my teachers and past professors, professionals working with this prefer the units for torque to remain $N \ m$ (Newton meters) to note the distinction between torque and energy.įun fact: alternative units for torque are Joules/radian, though not heavily used. If you think torque is measured in Joules, you might get confused and think it is energy, but it is not energy. ![]() Essentially, dot products return scalars and cross products return vectors. However, torque on the other hand, is defined as the cross product of $\vec r$ and $\vec F$ where $\vec r$ is the radius and $\vec F$ is the force. Where $W$ is the work done, $\vec F$ is the force, $\vec d$ is the displacement, and $\cdot$ indicates the dot product. Although this is algebraically the same units as Joules, Joules are generally not appropriate units for torque. The units for torque, as you stated, are Newton-meters. ![]()
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