Horsepower vs. torque

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by Silver3800V6FBodyKY:
Torque is work.

Work=Force x Distance
Torque= Force x Distance

Substitution: Work=Torque

Torque is not always rotational. If you move 10lbs. 5 feet, then the torque you applied to the 10lbs object to get it to move 5 feet is 50lbs.ft.

Also the work you did was 50lbs.ft.

Rotational or not, both are measured in force x distance.<hr></blockquote>

Ummm, no. Dominic is right. Torque is a rotational/twisting force. It is not work. Your substitution fails because the "distance" is different in each. The correct definition of torque is more like:
Torque = Force x Length of lever arm
Think about it like this... if you put a wrench on a bolt, then hold the wrench at the bottom of the handle, then the "distance" would be equal to the length of the wrench. If the wrench is 0.3m long, and I apply 100N of force perpendicular to the wrench, then I applied 30N*m of torque. One thing about torque is that there does not have to be any motion for there to be a torque. Just the applied force. Oh, and if you aren't applying it perpendicular to the lever, then you have to add in the a nice sin(theta) term to the definition.

Now to work:
Work = Force x Distance. So if I push a box along the ground 1 m and apply let's say 450N of force(about 100 lbs of force, if I did the conversion right), then I did 450N*m of work. I probably did not apply any torque to the box, since I did not give it any twisting force along an axis. Also, if I move the box 1 m forward, then move it 1 m back to start, I have done 0 N*m of work. Displacement would be a better term in the definition, especially if we are talking about net work.

Now, work done by torque. Here is the simple case where the torque is constant:
W = t*dtheta, where t is the torque and dtheta is the angular displacement (IN RADIANS of course ;) ).

EDIT: Sorry if I disappointed all the hardcore guys who like to see all the neat greek leters that appear in physics textbooks, but I feel this is an adequate explanation, and I think I even got it all right [img]smile.gif[/img]

[ September 04, 2002: Message edited by: HAZ-Matt ]</p>

[Silver3800V6FBodyKY]

Nonetheless, your car's torque is measured in ft.lbs.

So is your engine's work.

[HAZ-Matt]

Nevertheless, although the units may be the same, it does not mean that work = torque. If that was true, wouldn't the torque curve and the horsepower curve be the same? You're trying to call an orange an apple because it is a fruit. You're using the definition for work in a straight line, and applying it to rotational situations. You can't do that. That's why work in a circle is defined differently from work in a straight line. I gave you the definitions of both above.

Read the section called Rotational Work and Power

If you don't want to take my word for it, go get a physics book and see what it has to say, then post it for all of us to see.

[ September 04, 2002: Message edited by: HAZ-Matt ]</p>

[WickEdSix9838]

a horsepower motor will run faster than a torque motor...compare NHRA Pro Stock and IHRA Pro Stock, NHRA is running 500 c.i. and IHRA is running 814 c.i. yet NHRA is only running .2 slower than IHRA...

[Dominic]

Horsepower is simply a result of a certain amount of torque being performed in a certain quantity of time.

The more torque you can make, the slower you have to make it to generate the desired power. Conversely, the less torque you make, the faster you must make that torque to generate the desired power.

Looking at it from yet another angle, he who makes the most torque ALL ACROSS THE BAND, makes the most horsepower ALL ACROSS THE BAND, and therefore wins.

There is no competition between torque and horsepower, its simply that horsepower is a result of torque being performed at a particular RPM.

Thank you Haz-Matt for your explanation, you are correct.

[Dominic]

Also - you cannot feel torque. You only feel your *** slide back in the seat and thats sheer acceleration. This acceleration is a result of the torque your engine is performing + mechanical advantages through gearing.

If you clutch dump our cars at 4000RPM, the torque peak, you're not putting 225ftlbs of torque to the ground. No, actually, you're putting 225 * 1st gear ratio * final drive ratio = final torque to the ground.

Lets say youre driving a bone stock M5 V6 Camaro/Firebird and you clutchdump at torque peak.

225ftlbs * 3.75 * 3.23 = 2725ftlbs of torque to the wheels alone... then you must multiply that torque across the gearing your wheel circumference provides [img]smile.gif[/img] .

Eventually you can get a "net torque to ground" force, and see how well that equals the forward static friction force of your tires against the asphault with say 50% of your cars weight back there :D (just to simplify things, I know I need to integrate it for it to be exact, and take more precise measurements - give me a break).

And you wonder why we burn rubber :D

[ September 14, 2002: Message edited by: Dominic ]</p>

[AZ3.8Camaro]

<blockquote>quote:</font><hr> horsepower sells cars, torque wins races <hr></blockquote>

Then why aren't turbo diesels running 10s?

[FBodyFreakinIT]

<blockquote>quote:</font><hr> Then why aren't turbo diesels running 10s?
<hr></blockquote>

A number of reasons, foremost is probably that your average turbo diesel is not geared for running 1/4 miles. ;) It's geared to move you, your crap, and as much extra crap as you can pile on it.