Torque has been a noted topic in class as of late. Although we (the class in general) were unable to discuss the concept in any depth, several questions were asked concerning what torque is in reference to vehicles. In an attempt to help clarify the situation, an example is provided.
If a person were to go to a car lot and look at the technical specifications of a Ford Mustang Cobra, they may find that the Mustang generates ~437hp. This is an amazing quantity and enables the Mustang to be labeled as a sports car, and provides the power necessary to propel the car in speeds well in excess of 100mph (Nice). Now, if a the same person were to go to the Caterpillar lot and check the specs on a gigantic dump truck that is powered by Caterpillar’s giant C-12 diesel truck engine, they would notice that this engine also has a comparable ~430hp. If the person only noticed these quantities they may assume that these engines are very similar, when in fact they are very different (Nice).
The weight difference alone of the two engines amounts to 1600 lbs, besides the fact that one engine (Mustang) is gasoline powered, while the Cat engine is fueled by diesel. So what do these differences mean? Well, according to the web site,http://www.howstuffworks.com, these differences are very important with the operation of the industrial world. When the Mustang engine is operating at 5,600 RPM, it is producing 377 hp. The Cat engine on the other hand, while operating at 1200 RPM, is also producing 377 hp; so there is a very noticeable difference in RPM values in order to achieve the same amount of horsepower. This difference in RPM’s is mainly attributed to the difference between diesel and gasoline engines, and becomes a topic all of its own. The most important difference however, is the difference in the torque values at these operational speeds. While at 5600 RPM or 377 hp the Mustang is producing 354 lb-ft. of torque, while the Cat operating at an equal horsepower value produces an astonishing 1,650 lb-ft of torque. Using a gear ratio 4.66:1 enables the Mustang to also produce 1,650 lb-ft of torque, while it is operating at 5600 RPM and producing 377 hp.
So what does these torque values mean? The best way to explain it is the idea of how these two different engines are used. The Mustang engine is used to propel a relatively small sports car weighing one or two tons, while the big Caterpillar engine is used to lurch gigantic mining trucks up steep inclines carrying loads of 40+ tons. So the torque becomes the deciding factor in how much weight a vehicle can move. So when looking at vehicles, those with the largest amount of torque (specifically trucks) also have the greatest capability to move a large load, in the same way that the large amounts of torque are required to move the large mining truck. As a side note, this is why large industrial vehicles such as: dump trucks, semi trailers and motorhomes usually contain diesel engines. The reason becomes fairly obvious. Referencing back to the previous example, the diesel engine was able to produce large amounts of torque at low RPM values and with no gearing reduction. The Mustang on the other hand would have to operate at 5600 RPM and be reduced using gears to obtain the same amount of power to move the large vehicle. Because the diesel engine operates at such low speeds, with fewer mechanical parts, it becomes the engine of choice for most vehicles of large size and weight.
I personally like to compare torque to leverage. For example, if I weigh 150 lbs, and I were to stand on a 1-foot long wrench that was positioned on a bolt, such that the handle would be parallel to the floor, I would be exerting a torque of 150 ft-lbs. This example is only valid if my force is perpendicular to the handle of the wrench, and this is why it would be important for the wrench handle to be parallel to the floor. If I were to then extend the length of the handle to 2 feet, I would then be exerting a force of 300 ft-lbs. This additional torque created would enable me, or give me the leverage, required to tighten the bolt with less effort. And when in doubt, one can always refer to Webster’s dictionary for a definition of torque, this reads:
torque1 Pronunciation Key (tôrk)
Nice, Karim. "How Force, Power, Torque, and Energy Work."