dumb question but need help

ok u guys probibly think its really dumb but i dont exactly get torque..
i know it like foot pounds n stuff.. but thats as far as i got..
could someone plz explain this to me .. better.. lol
thanks alot


oh and im just learning bout cars so if u could fill me in on some other stuff or tell me what i can do to learn more that would be awesome.... i know its alot to ask for but worth a try..thx

its pretty simple.

torque is a static measurment of force.
in relation to an engine, it is a measurement of how much work an engine can do.
hosepower is (in engine-speak) torque x rpm

basically, think of it like this.

torque is how much work an engine can do.
horsepower is how quickly it can do that work.

but what does foot pounds have to do with all of that??
and thx for the reply

it's the measurement used for rotational force.

rotational force.... as in the crankshaft?
lol

well foot pounds is a unit of measurment of torque.

it is like this.
if you are tightening a bolt, and you have a 2 foot long wrench and put 50 pounds of force on to the end of the wrench, you are putting 100 foot pounds of torque on the bolt.
same with a 4 foot long wrench and 25 pounds of force.
or a 1 foot long wrench and 100 pounds of force

when measuring torque on an engine, the dyno is measuring the ammount of torque that the engine can produce as the dyno is resisting the rotation of the wheels/crank

the dyno then converts this information to horsepower.

Torque is a twisting force.

Put a 1lb weight on a lever 1ft long and you get 1 fl-lb of torque at the end of the lever.

the dyno then converts this information to horsepower.
*cough* other way around. Dyno measures the drum acceleration at X mph over X time (aka "work" over "time"...with a intertia drum dyno anyway) which is converted to HP then converted to engine torque

In short, torque is a static measurement. It does not involve movement and time. As soon as time and movement is involved, its HP. HP is a dynamic measurement. (ie real-world)

Torque is not work done. Work done means something has moved. You can apply torque w/out doing any work. It can be simply put as

Torque = Force x Radius

Better off put, Torque is a cross product between the radius and force.
t = F x r. But that touches on vectors and may not be appropriate for this thread.

In short, torque is a static measurement. It does not involve movement and time. As soon as time and movement is involved, its HP. HP is a dynamic measurement. (ie real-world)

Didn't even see that in your post. +1

Torque is not work done. Work done means something has moved. You can apply torque w/out doing any work. It can be simply put as

Torque = Force x Radius

To continue along those lines:

Work done (Joules) = Torque (Nm)*Rotation (radians)

Power (watts or joules/second) = Torque(Nm) * Rotating speed (radians per second).

To continue along those lines:

Work done (Joules) = Torque (Nm)*Rotation (radians)

Power (watts or joules/second) = Torque(Nm) * Rotating speed (radians per second).
if this was right it would mean that work is measured in N * m * radians. it's just newton meters, which are equivalent to joules. as well, power is work/time and work is measured in newton meters, time in seconds, this would mean power = Nm/s, not Nm*radians/s.

if you want a vector definition of torque, then it's the cross product of the force and the distance from the point where the torque is applied (and it's r X F, not F X r, i got screwed with that mistake on my exam this year). it's pretty much a measure of a rotational force on a point, with no time or movement involved.

when applying it to cars, it's how much rotational force the engine can apply at a certain rpm. horsepower is how much work the engine can do in a certain ammount of time.

since work (w) equals a force over a distance (F*d) then power is how quickly you can apply that force over that distance. so if you have 100 Watts (N*m/s) you can apply 100 Newtons over 1 meter in 1 second, 50 newtons over 2 meters in 1 second, etc.

hope this clarified things up, i find it more difficult to think of torque relating to cars vs torque relating to wrenches and such (although a wrench system is different from what you think it is, as i learned in mechanics I this year)

well thats why the units are different.

wrench torque is measured with different units than car torque.
one is lbft one is ftlbs... i dont remember which is which, but they are completely different.

BUT...
in both cases, torque is measuring a force that is static and not related to time.

wrench torque is measured with different units than car torque.
one is lbft one is ftlbs... i dont remember which is which, but they are completely different.

nope, they're the same.

it's a personal prefrence thing, some people say ft-lbs and some say lb/ft.

still pounds per foot.

right but seeing as how they are so different, it is sort of agreed that wrench torque is meausred with different units than car torque.
at least thats how it is here in the US

never come accross that.

i've also known ft-lbs and lb/ft as the same thing, exactly the same. we get torque wrenches in lb/ft or ft-lbs and they're the same except for whether the manufacturer puts lb/ft or ft-lbs on the gauge.

right but seeing as how they are so different, it is sort of agreed that wrench torque is meausred with different units than car torque.
at least thats how it is here in the US

i agree with 2.2, they're the exact same thing, same units, same concept, that's how it's measured in canada, the us, and the UK. the units for torque differ in the SI (system international) system, the EE (english engineering), and US systems. in the SI system (what most of the world uses) it's Nm (newton meters), in the EE (aka the english gravitational) system it's in lbf-ft (pounds-force foot), and in the US system it's lb-ft (pounds feet).

the difference, to reiterate, is torque wrenches quite often involve no "work" (ie motion/movement/time), where as engines always involve "work"....since they have to be rotating to run.

If we were discussing electric motors, for example, they can produce a lot of toque with no motion

max torque @0rpm.

if this was right it would mean that work is measured in N * m * radians. it's just newton meters, which are equivalent to joules. as well, power is work/time and work is measured in newton meters, time in seconds, this would mean power = Nm/s, not Nm*radians/s.

Back to school for you.
Dot product vs Cross Product.

Nm are the units of torque (cross product)
Nm are also the units of work (dot product)

Converting work to power is as simple as dividing by time.

Radians are a dimensionless unit.

thats it...
i was in math class today and was trying to remember what the unitless unit was.
radians of course.

Back to school for you.
Dot product vs Cross Product.

Nm are the units of torque (cross product)
Nm are also the units of work (dot product)

Converting work to power is as simple as dividing by time.

Radians are a dimensionless unit.

kk i wasn't sure what you meant by radians, i though you were refering to an angle. and yeah, i knew about the cross product being torque (also known as a moment about a point, line or axis) and the dot product being work, it was just the radians that messed me up.

kk i wasn't sure what you meant by radians, i though you were refering to an angle. and yeah, i knew about the cross product being torque (also known as a moment about a point, line or axis) and the dot product being work, it was just the radians that messed me up.

Radians are an angle.
2pi radians in a complete revolution. One radian is approximately 173 degrees.

i thought it was more like 57.

360* / 2(pi) = 57.29

Radians are an angle.
2pi radians in a complete revolution. One radian is approximately 173 degrees.

yeah, but when you're finding work and torque you don't multiply the two together then multiply by the angle, you multiply by either the cosine of the angle or the sine of the angle. radians do have units, the sine, cosine, tangent, etc, of them don't.

i thought it was more like 57.

360* / 2(pi) = 57.29

Right you are, not sure where I got 173 deg from.:wink:

yeah, but when you're finding work and torque you don't multiply the two together then multiply by the angle, you multiply by either the cosine of the angle or the sine of the angle. radians do have units, the sine, cosine, tangent, etc, of them don't.
Torque is already resolved into tangential forces acting at 90 deg. Hence sine and cosine of the angle aren't needed (sine 90 = 1, cosine 90 = 0).

A radian is a length ratio, (arc length/radius). For a circle measured in metres the units are (metres/metres), which cancel each other out to become a true dimensionless factor.


Work = torque(Nm)*angle(radians).
Power = work/time
= torque(Nm)*angular velocity(radians per second).

why use radians any way?
they have such limited use, and degrees are so much easier to explain (and understand)

why use radians any way?
they have such limited use, and degrees are so much easier to explain (and understand)

To use degrees requires a more complicated formula.
Revolutions is the easiest to explain but radians makes more mathematical sense.