* How Stuff Works - An Introductory

[All Wheel Drive]

Originally Posted by thepolarfoxqx a newton meter is one newton's force extended over a leverage of one meter, so it is a newton times a meter.

Then, there are some parts that need to be rectified... a 100N force applied to an arm that has 2 meters delivers 200Nm of torque not 50Nm, isn't it?

[GIR]

I think you're reading it wrong or are confused with something else. Here's the full text once more:

If you have a lug nut and you have a wrench that is 1 meter. When you put 100 Netwon of force on the wrench you are generating 100Nm of torque. If your wrench is 2 meters long then you generate the same amount of torque but the amount of enegery required is just 50 Newton.

So to pull it apart even more:

Length from center = 1 meter
Force = 100 Newton
Torque = 100Nm

Length from center = 2 meter
Force = 50 Newton
Torque = 100Nm

So the end result, the amount of torque, is the same but you need to apply less force on the wrench.

[All Wheel Drive]

U'r right, I was reading it wrong. My mistake reguarding this one. Sorry!

[thepolarfoxqx]

to answer a previous question about air resistance, rolling resistance is something else, and often it is far less than air drag. Air drag is the resistance from the car relocating the air in the space it travels through, like when you stick your hand out the window while driving and the air tries to push it back, it does the same thing to the body of your car, and it gets exponentially stronger as you get faster.

[reggid]

i am well aware of what air resistance is, but what is the drag that is mentioned in the first post? Maybe GIR can elaborate a bit!!!

It is correct that if you double the length of the spanner you do need only half the force to achieve the same torque, but you require the same energy to do so (conservation of work or energy). This is because torque and energy have the same units Nm (if you keep torque constant the energy required will be the same).

Although i said that torque and energy have the same units this does not mean they are equal!!!

For some reason it is also mentioned that force (Newton N) is equivalent to energy(Newton Metres Nm or Joules J) which is not correct.

[GIR]

Yeah yeah yeah bla bla bla, sighs there's always somebody who has to complain about some technicality. Yes the total energy is the same (because nobody can create energy) but the distance travelled is longer hence the amount of force required is lower. I should really get somebody to proof reed these to avoid these situations.

The point of this article is to give a basic introduction to simple things not to explain to whole workings of the physics system.

As I stated in my original article the original drag you have is the drag from (among other things) the road. A object that's standing still always wants to stand still. In the initial phase it's point to overcome this initial drag because while pulling out from a line it's the most. After you've overcome this drag another law comes into play and that is that an object that's moving always wants to stay in that motion.

You can vefity this by doing the following. Get a cardboard box and fill it with some very heavy stuff. Then just give the box a little push. The box won't budge. Then push it constantly. You'll notice that at first you'll have alot of trouble getting the box to move but once you get it moving it becomes easier the faster you go.

[thepolarfoxqx]

GIR, you could have just said it easily back to him that he should have known that work (or energy) is simply force times distance, so torque (force) times distance travelled is work done on moving the vehicle.

[reggid]

I think i now know what you mean, friction in the bearings amongs otherthings etc, the effect of the frictionional difference between sliding surfaces and non sliding (kinetic and static to do with cardboard box more specifically).
Though at low speed i think rolling resistance is more significant than any other effect apart from the handbrake.
A car tyre pumped up to the proper pressure will roll easier and hence be more fuel efficient than a softer tyre, as would steel wheels if they were practicle for a car.

[GIR]

No not quiet. All the moving parts cause drag aswell, that is true and this drag has to be overcome aswell but it's infinitely small compared to the drag cause by the road itself.

You can view it like this. Your car wants to move forward so it excerts a force onto the road. But the road doesn't like this so it tries to hold the car in place as much as possible. The faster you go the smaller this drag becomes. Well the amount of force excerted onto the road is infinite times bigger then the drag cause by the road so we can say that it's actually not there.

If you want it in equation form look at it like this:

y(x) = x/(1+x)
the 1 represents the drag

Now lets say x = 1 (accelerating from standstill)
y(1) = 1/(1+1) = 1/2 = 0.5

Now lets say x = 10 (still acellerating but somewhat further)
y(10) = 10/(1+10) = 10/11 = 0.909

now lets jump a little forward and lets say x = 10000
y(10000) = 10000/(1+10000) = 10000/10001 = 0.99999999999999999

When x = 10000 then we can say that the 1 (representing the drag) is so small compared to the x that we can infact leave the 1 out and say it's not there anymore. While infact it's still there but it's so much smaller then the total energy you won't feel it anymore.

[thepolarfoxqx]

GIR gave the the same familiar headache i remember from early morning calc lectures.

i understand math very well untill you just start piling number on me.