Discussion in 'General Chat' started by blacknight, Sep 1, 2010.
Difference between HP & torque
nice thread BN
Difference between Hp and Torque, HP is how fast you hit the wall torque is how far the wall moves.
Or: Torque is the capacity to put an object into acceleration, HP is the capacity to maintain & produce force. So lets say you can accelerate at 10m/s² with X HP, torque definite how fast you will reach that acceleration rate.
That's how it goes engineering wise.
In laymans term..
Torque gets you moving.
HP keeps you moving
I like the analogy of a weight on the end of a wrench for torque. In fact, I use that method when I'm torquing something like lug nuts. If my wrench is 2ft long, I weight 150lbs, and I need to torque it to 100lb/ft, I divide the lb/ft in half (because of the 2ft wrench), and put 1/3 of my weight on it (50lbs).
The explanation of HP is a little ****ed though. HP = TQ x RPM / 5252.
Power is how fast you can make torque. The analogy to a bicycle was good there, but they didn't explain it very well. At the pedals (or crank), assume the pedal arms are 1ft long, and I still weigh 150lbs. The maximum torque I can make at the crank is 150lb/ft, at zero RPM. The faster I pedal, the less of my weight I can get onto the pedal before it's down and I must switch to the other foot. My redline would be the fastest I could possibly spin the pedals, probably about 60rpm, and I would make pretty much 0 torque there.
If you graphed that you would have my torque curve.
At 0 RPM I would make 0 HP. Because torque, without movement, is nothing.
At 60 RPM I would make 0 HP. Speed without torque is also nothing.
At 30 RPM....
30 x 75 = 2250
2250 / 5252 = 0.42 HP!!!
Remember this is all at the crank, no matter what gear, I make 0.42 HP at 30RPM
Power is conserved, sort of, we'll just ignore friction losses. Lets say the bike has only 3 gears. Low, Direct, & Overdrive. Low gear is 2:1, Direct is 1:1, and Overdrive is 1:2.
In low gear at 30rpm, my rear axle would spin half the speed of the crank, or 15rpm. I would still have 0.42HP, so torque, at the back, must go up. That's the point of low gear. I would have 150lb/ft of torque at the rear axle.
Direct is just that. What goes in is what goes out. On old RWD cars, before overdrive was common, this was the top gear, 3rd or 4th. Hence the nomenclature of 'over drive', which.....
In overdrive the rear axle spins faster than the crank. At my 30 RPM, the crank would spin at 60 RPM, but I still have only 0.42 HP so my torque MUST decrease. I would only have 37.5lb/ft of torque available at that rear axle. No hills in OD.
In a car, after the transmission is a final drive, the differential, which further reduces RPM to give torque. A '4.10' or '3.73' refers to the reduction, that's 4.10:1, or for every 4.1 turns of the driveshaft, you get 1 turn of the axle, of course that also multiplies the torque by 4.1 though. This is done in the differential because big torque needs big parts, like why you don't use a 1/4" ratchet to remove your lug nuts. If you're transmission had to do this, all of the gears would need to be about 4 times larger, and it would weigh about as much as the car.
You can apply this to electrical too. Watts are power, in fact there are 747 watts in one HP. Volts X Amps = Watts. Volts could be described as RPM, because it's potential. Amps would be like torque because the more there are, the bigger the parts need to be. And again, one without the other is nothing.
But here's the kicker....
Without some type of measuring device, how can you accurately determine a 1/3 of your weight?
You can't, but it's better than kicking the **** out of the lug wrench.
I probably can, but I turn wrenches every day. Though I typically use a digital torque wrench, but sometimes you just don't have one.
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