Help with understand the concept of torque

[chound]

What is torque

 

[ceptimus]

Torque is a turning force. It's measured in units like foot-pounds where you multiply the force applied to a lever by the lever's length. So if you pushed with a force of 40 pounds, on the end of a two foot long wheel nut wrench, you'd be applying a torque of 80 foot-pounds to the wheel nut.

The torque output of engines is often measured. The power output of an engine is proportional to how much turning force it can generate, and at what speed (revolutions per minute) it generates it at. To double the power of an engine, it could make the same torque at double the rpm, or it could produce twice as much torque with the speed unchanged.

The scientific units for torque are Newton metres, and the scientific units for turning speeds are radians per second. If you multiply these together, you get a power output in Watts.

 

[chound]

is it better to have higher torque in cars?

 

[Gonzolo]

If you want better acceleration or want to pull heavier loads, yes.

 

[ceptimus]

is it better to have higher torque in cars?

Most people would answer, 'yes'. But the only place you actually need torque in cars is at the wheels. The job of the engine is to produce power not torque.

Given a perfect transmission - one that would always alow the engine to run at its peak efficiency RPM to produce the required power, and transmit that power to the wheels without any power loss, then engine torque would be of no interest to the car driver. It's only because real world tranmissions are far from perfect that we care about the torque curve of engines.

 

[krab]

is it better to have higher torque in cars?

Engine speed remaining equal, yes it's better to have more torque because that means you have more power. OTOH, if you are comparing 2 cars where car A has more torque (at the crankshaft, since that's usually what's meant), but the same power as car B, then the answer is no. You just gear car B differently (lower), and it has the same performance. (This re-iterates Ceptimus, but it is always helpful to hear the same things explained in more than one way.)

 

[Chronos]

Ceptimus gave an excellent explanation, as confirmed by krab. Torque is also called a moment or coupling force. It originated with the Archimedes concept of levers. Torque is what you get when you translate a lever applying force, mass and acceleration, from cartesian to polar coordinates.