8th Generation Honda Civic Forum - View Single Post - Everything You Wanted To Know About Car Measurements(HP, TQ, Gear Ratios etc.)

ryker · 12-14-2007, 08:29 AM

I'll post several links and quotes. This is not my .02 but simple math. Pictures will follow later today. Makes it easy to see and understand with the pics!

Horsepower and Torque - Craig's Website at Backfire.ca

Torque

Torque is a force that tends to cause a rotation. A force applied at a non-zero distance from an object's centre will tend to rotate the object. This is easily seen in real life. If you put a wrench on a bolt and pull on the end of the wrench, the bolt will turn. If you apply the same pulling force directly on the bolt, it will not turn, because the force is not distant from the object's centre. The amount of torque is determined by multiplying the magnitude of the force by the force's distance from centre.

Work

Work is something that is not talked about much when talking about cars. Work is defined as the transfer of energy from one system to another, such as a person pushing a box across a floor. Mathematically, work is a force times a distance, and has units such as foot-pounds or Newton-metres. The direction of force (or at least a component of it) must match the direction of motion for the force to be considered to be doing work.

The force is doing work on the object, because it is causing the object to move along a distance.

Difference Between Torque and Work

Notice that the units for torque and work are basically the same, yet torque and work are two different things. Torque is a force that causes a rotation, which means that it does not actually cause an object to move along a distance. Therefore, torque is not work.

The difference between torque and work.

On a rotating shaft, the work is done by the torque. This is because torque is a force about a circle, and the shaft is a circle. The force is going round and round, and so is the shaft, so if we "unroll" the shaft, we have a force traveling across a linear distance. That's work.

On a rotating shaft, the torque is doing the work.

Power
not horsepower but Power.

Power is the amount of work that can be done in a certain amount of time, or "the rate of work", or "the rate of energy transfer between systems". Therefore, the units for power are in the form below:

Power is always a force multiplied by a distance over a period of time.

The above equation can be rewritten in terms of force and speed, as seen below:

Using the definition of speed, power can be expressed in terms of force and speed.

Shaft Power

On a rotating shaft (like an axle), the torque is doing the work, and the shaft's rotational speed is time-dependent, so shaft power is the product of its rotational speed and its torque. Using arbitrary units, the power formula for a rotating shaft is:

Shaft power using arbitrary units.

12-14-2007, 08:29 AM	#16 (permalink)
ryker Senior Member Join Date: Sep 2007 Posts: 10,065	I'll post several links and quotes. This is not my .02 but simple math. Pictures will follow later today. Makes it easy to see and understand with the pics! Horsepower and Torque - Craig's Website at Backfire.ca Torque Torque is a force that tends to cause a rotation. A force applied at a non-zero distance from an object's centre will tend to rotate the object. This is easily seen in real life. If you put a wrench on a bolt and pull on the end of the wrench, the bolt will turn. If you apply the same pulling force directly on the bolt, it will not turn, because the force is not distant from the object's centre. The amount of torque is determined by multiplying the magnitude of the force by the force's distance from centre. Work Work is something that is not talked about much when talking about cars. Work is defined as the transfer of energy from one system to another, such as a person pushing a box across a floor. Mathematically, work is a force times a distance, and has units such as foot-pounds or Newton-metres. The direction of force (or at least a component of it) must match the direction of motion for the force to be considered to be doing work. The force is doing work on the object, because it is causing the object to move along a distance. Difference Between Torque and Work Notice that the units for torque and work are basically the same, yet torque and work are two different things. Torque is a force that causes a rotation, which means that it does not actually cause an object to move along a distance. Therefore, torque is not work. The difference between torque and work. On a rotating shaft, the work is done by the torque. This is because torque is a force about a circle, and the shaft is a circle. The force is going round and round, and so is the shaft, so if we "unroll" the shaft, we have a force traveling across a linear distance. That's work. On a rotating shaft, the torque is doing the work. Power not horsepower but Power. Power is the amount of work that can be done in a certain amount of time, or "the rate of work", or "the rate of energy transfer between systems". Therefore, the units for power are in the form below: Power is always a force multiplied by a distance over a period of time. The above equation can be rewritten in terms of force and speed, as seen below: Using the definition of speed, power can be expressed in terms of force and speed. Shaft Power On a rotating shaft (like an axle), the torque is doing the work, and the shaft's rotational speed is time-dependent, so shaft power is the product of its rotational speed and its torque. Using arbitrary units, the power formula for a rotating shaft is: Shaft power using arbitrary units. Last edited by ryker; 12-14-2007 at 01:14 PM.