Honk if you could use 775 ft-lbs

[romafan]

Is this what Paris Hilton was driving?

Sorry for the stupid question, but what is '775 ft-lbs'?

 

[j]

A ft-lb is a foot-pound, a measurement of torque - it is the effort required to move one pound one foot, or something like that. I think the metric equivalent is measured in Newton-meters.

775 ft-lbs of torque is a hell of a lot.

 

[Huntsman]

Eh, almost. I'm a mech E, can't help it. The definition of torque (a measurement of rotational force) is force 'crossed' (the mathematical cross product) with distance, i.e, the force times the perpendicular distance from the point of application to the center of rotation. In general use, the length of the useful part of the wrench you're grunting on. The appropriate unit is lbf-ft -- pounds force times feet. A foot-pound, abbreviated ft-lb, is technically a measure of energy (which is force times a distance), not simply force itself, which torque is the rotational equivalent of. These are commonly swapped. A useful extension is the relationship of torque to horsepower. Hp is a measure of work, which is force that is allowed to cover a distance in time, and is expressed as force per unit time, so hp tells you that so much torque (force) is acting over a certain distance, in a given amount of time. One hp is 550 foot-pound force per minute. From this it falls out that if you are grunting on a wrench and not turning the bolt, you may be applying torque (force to induce rotation), but since no distance has been covered, technically you've done no work and exerting precisely zero power. And yeah, 775 lbf-ft is a lot! I have this big honking 3/4" drive torque wrench with a 3ft long handle that I think hits 400, and it's absurdly huge. Regards, Huntsman

 

[j]

Good explanation, but this thread is about engine torque, not a gigantic bolt.

 

[Huntsman]

Heh, yeah, I know. Same difference, though. They sometimes use these 3" diameter bolts amd nuts at work and I'm trying to get me one for my desk. Heck of a paperweight.

 

[tiecollector]

This definition gives you a better idea of where the name comes from: foot-pound, abbr. ft-lb, unit of work or energy in the customary English gravitational system; it is the work done or energy expended by a force of 1 pound acting through a distance of 1 foot. It is equal to 1.356 joules. The term foot-pound is also used to designate a unit of torque that is sometimes called the pound-foot to distinguish it from the energy unit. A force of 1 pound applied 1 foot from and perpendicular to the direction to an axis of rotation produces a 1 foot-pound (or pound-foot) torque at the axis. J was close. Though, it is still tough to gauge how strong 775 ft-lb is by the definition if you aren't used to thinking in these terms, but I'm sure it is an incredible amount.

 

[tiger02]

Incredible amount = almost two full M5s. Yeah, I'd call that a "**** ton" even.