Car engines - torque and power output?
This is for a physics project so if possible i would need heaps of help.
Thank you
Answer:
So many use these words and so few know what they mean. Work first. This is force through a distance. It doesn't matter of you apply one pound over a ten foot distance or two pounds over a five foot distance, you've done ten foot pounds worth of work. Power is how fast you do it. If you can do 550 foot pounds of work in one second, that's one horsepower. Gives you greater respect for the horse, doesn't it? Anyway, you can change the direction that you're pulling in, but you have to keep pulling. So you can pull in a circle, like turning a crank. If you push on the handle of the crank with five pounds of force and the arm of the crank (radius) is two feet, you are applying ten foot-pounds of torque, NOT the same as the ten foot-pounds of work mentioned before so it's sometimes called pound-feet to distinguish, but you have to know the difference.
If you apply force but don't move the crank you've applied a torque but haven't done any work, just as you haven't done work if you apply force to an object but haven't moved it. It's only when you've moved something that you've done work.
In rotary motion, the crank arm (radius) is r, and the distance in one revolution is 2¶r. So if you apply a ten foot-pound torque, it tells nothing about the work. But if you apply the ten foot pounds through one revolution of the crank, you've done 5 pounds X 2 feet X 2 X 3.14 = 62.8 foot-pounds of work. You can change the force and moment arm any way you want to get the same torque, and you'll still get the same amount of work through one revolution with the same torque. Try it.
But notice that is work and not power, because we haven't established how fast you're doing it. In order to make one horsepower, you have to do 550 foot pounds per second, or turn that crank in 62.8 ft-lb / 550 ft-lb/sec = 0.114 seconds. The equivalent rotary speed would be 60 sec/min / 0.114 sec/rev = 526 rev/min. So a TORQUE of ten foot-pounds at 526 rpm would give a POWER of one hp. When you're done with that, mow the lawn.
As often happens in a car engine, your torque falls as the engine goes faster. But if the engine gains speed faster than the torque falls off, you're still making more power. That's why when they're graphed together, the torque peak is at a lower rpm than the horsepower peak. Torque and horsepower are related by rpm. Know one and you know the other.
powerblock.com
The torque of an engine is kinda how hard the engine is pushing, and this is inversely proportional to the speed...
Picture it like this; you're cycling on your bike making say 60 rotations per minute (rpm) and you're on a LOW gear, this makes the wheel rotate slower but with more grip. This has high torque and is good for uphill.
However, if you're still peddling at 60 rpm, and you're on a HIGH gear, then the wheel speed will increase but there is less torque. This is good for flats or downhill.
i think this site will help you a lot:
www.howstuffworks.com
car engines are generally classified as per engine cylinder volume in cc which nturn is indicative about its H.P .
Torque is related to H.P as follows
H.P = 2 X 3.142 torque x N / 33000 where torque unit is ftIbs
and N in rpm. You have to refer car catatalogues to know engine volume/power capacity of the model and then you can find the rest yourself using above formula.
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