This isn't uk.basic-physics but I'll give it a go. Torque is the rotational force exerted by the engine. Power is the amount of work being done by the engine. The power can be calculated from the torque (or vice-versa): power = torque x angular velocity.
Hum, fairly sure thats the rev limit on my TD5 which is most definately not a racing engine (mind the 2+ tonnes of vehicle weight might have something to do with that).
I think I've only taken it that high a couple of times, once to see what happened (nothing much the revs just stop increasing, nothing dramatic as has been implied in this thread) and maybe a couple of times in second "to get out of trouble".
Quite right - thanks. It's fifty years since I was taught that stuff in school. It's a tribute to my teacher (Mr Ellis) that I still remember it (even imperfectly) after all that time.
energy is work done more or less. power is first differential of that wrt to time. torque is a measure of force applied around and axis. work done is torque times revolutions. Power istorque times number of revolutions in a given time. So (removing all the constants) power=torque times RPM.
Coming back to driving, the point is that maximum acceleration corresponds to maximum power, not maximum torque. Typically a petrol engine has much less than maximum power at cruising speed, so you need to change to a lower gear to accelerate briskly. A diesel engine gives close to maximum power at cruising revs, so you don't need to change down. (The difference is more obvious with a manual gearbox than an auto, because of the time and effort required to change down manually.)
WIWAL we compared the power of engines. Nowadays the pundits like to bang on about "torque", and diesel torque is often compared favourably with petrol torque. Torque is not a particularly useful indicator of available acceleration, *unless* you discount the possibility of changing gear (and why would you?).
MM. its is relevant because of the issues of number of gears and gear changes. The original F1 honda engine was massively powerful, but at such a narrow rev band that it didnt actually deliver best acceleration. They tamed it a bit and got better results.
If you are beyond 'wheelspin' power then tractability is more use.
The fasted rate of change of speed of the vehicle (acceleration) will be at maximum torque. In the lowest gear - assuming it retains traction. However, if you change up a gear at peak torque, you'll now likely be well below that in the higher gear so lower revs. A well designed gearbox would allow the engine speed to be kept roughly between peak torque and peak power for best acceleration.
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