Hippie wrote:sped372 wrote:Work is work. What does the work? Burning fuel (potential energy)! Theoretically, if you're doing the same amount of work, you'd use the same amount of energy. It shouldn't matter which gear you're in... less torque x more rpms = more torque x less rpms = same amount of work.
But at higher RPM, there are more bangs per second = more power in, more power out.
Not quite... think about it. The end product is moving the bus down the road. Let's arbitrarily choose a vehicle speed and work from that... say 35mph? If you're going down the road at a constant 35mph you can assume that you require a constant amount of power (work) to get the job done. If the engine was producing more power/work the bus would speed up... less power, it slows down. You're overcoming air resistance, rolling resistance, and all those other little parasitic items that keep perpetual motion machines out of our reach. Lets just arbitrarily guess that a bus needs 15hp to drive at a constant 35mph.
Now, it doesn't matter what gear you're in... that has no effect on all those resistances you're overcoming (except the ones internal to the engine that are rpm dependent). In fact, you don't even need to be in any gear, or have the engine running! The fact remains that
somehow, you need to come up with 15hp to keep that bus moving at 35mph. Well, we're lucky and we have an engine and a transmission so we have options. Let's see, I could get my 15hp in third gear... so I'd need a certain amount of torque (from the engine) at a certain rpm, through the transmission, to the wheels to get me 15hp. Or, I could go in fourth gear, I'd need more torque from the engine, but at a lower rpm, through the transmission, to the wheels, to get me the same 15hp. If I didn't get 15hp I'd speed up (or slow down). Make sense?
Just because there's more bangs doesn't mean you're producing more power. That's what the throttle is there for. Each individual bang at a higher rpm is producing less power so that the cumulative total is the same. The engine has the potential to create a certain amount of power/work... you use the throttle to dial it back to where you need it.
Wheel torque is completely dependent on engine torque, the transmission is just a multiplier - it doesn't "create" any torque.
If we continue with the thought process, you could conclude that if you were able to roll down a hill in neutral at a steady 35mph you would be reducing your elevation at a rate of 15hp. Height is one form of potential energy. Fun stuff to ponder while your brakes are fading.