dumb question but need help

[beef_bourito]

Originally Posted by GreyGoose006

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).

[UncleBob]

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

[2.2 Straight six]

max torque @0rpm.

[KiwiBacon]

Originally Posted by beef_bourito

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.

[GreyGoose006]

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

[beef_bourito]

Originally Posted by KiwiBacon

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.

[KiwiBacon]

Originally Posted by beef_bourito

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.

[GreyGoose006]

i thought it was more like 57.

360* / 2(pi) = 57.29

[beef_bourito]

Originally Posted by KiwiBacon

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.

[KiwiBacon]

Originally Posted by GreyGoose006

i thought it was more like 57.

360* / 2(pi) = 57.29

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

[KiwiBacon]

Originally Posted by beef_bourito

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).

[GreyGoose006]

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

[KiwiBacon]

Originally Posted by GreyGoose006

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.