Well, sorta. Centrifigal force is a so-called pseudo force which allows a person in a non-inertial (accelerated) reference frame to pretend that he's in an inertial reference frame so he can, for instance add the forces and pseudo forces and get the right values for acceleration.

For instance, if a car is going around in a circle at a constant speed, the forces acting on it are gravity downward, the normal force from the road upward (which have to balance since the car's not accelerating vertically), and the frictional force which is providing the centripital acceleration which keeps the car going in a circle and is the square of the speed divided by the radius of the circle. But, imagine you've covered up the car windows so someone inside the car couldn't tell they were going in a circle. All they would know is there's an apparent force outward and that's the centrifugal pseudo force.

I know you were thinking that when you said they're the same thing and was just being less pedantic about it but I can't resist a physics discussion.

Mark

 

As soon as there's one physicist, you have AT LEAST two opinions on everything

Matt

 

Heh! I still hang out with a lot of physics geek friends, many from my college days, and we have the most ridiculous physics discussions over dinner. Then we spend half an hour trying to calculate what we each owe and it never, ever works out correctly.

Mark

 

Heh! I am in college hanging out with my physics and engineering geek friends . Although our discussions usually turn to how much work our Statics professor gives or how we can do to make money - which never works out.

 

here is a physics question/riddle for you:


you are lost in the hills, fortunately carrying a backpack of electronic gear of your choice, including a power source (no GPS!). you walk under a power line. Knowing there is a generating station within a mile which way do you walk? The physics question is really how can you tell which end of the power line has the load and which the generating source?

was on a masters/phd qualifier exam i took a long, long time ago.

 

Well, as we all know, electrons run from + to -, or from left to right, therefore, turn left to get to the generating station.:smile:

 

Cut the lines. Whichever end still electrocutes you is the source!

Would that have gotten full marks?

 

great answer! but they said no touchee.

you might get a pulse of reverse EMF from some motor load anyway.

 

If you have a magnet, you could find out which way the EMF from the line pushes it by bringing them close. Then using the right hand rule, you can calculate which way the power source is . Boy I just finished E & M and I still hate it. Gauss and Coulomb, eat your hearts out.

 

alternating current.


I always thought the Poynting vector was the way to go, but never figured it out.

 

19 and 22mm seem to be the prevalent upgrade options for the rear sway bar. Which one would you folks prefer for an otherwise stock suspension? The default for me is to get the biggest rear bar possible. I'm accustomed to AWD-pig understeer and doing everything in my power to counteract it. I'm hoping the 22mm bar would not be overkill for a stock MINI. Opinions?

 

So in your backpack full of stuff, do you have one of those clamp on current probes? They wouldn't touch the cable, but of course there is the practical matter of getting the thing up to the cable and clamping it around it.

However, I think you could do it easier (and at ground level) with a couple loops of wire to detect which way the mean magnetic field is going around the line. . .

 

If you go hiking in the woods with only electronic gear, and manage to get lost within site of power lines, you are to stupid to figure this one out. Just pick a direction and walk. You have a 50/50 chance of getting it right. If your wrong, you're only 2 miles away

 

the problem you are overlooking is that while you can use the inductive effect to measure current, the current switches direction with the AC voltage, and so does the magnetic field.


My intuition says the answer lies not in measuring current or voltage, but in some measurement of the power flow, hence the Poynting vector suggestion

 

That's why I had the word "mean" in there If there is power going down the line, there is a mean current flow down the line. Since the magnetic field comes from the current, there would be a mean direction to the field, as well. Remember what the 'M' in 'RMS' stands for. Just because something is AC doesn't mean there isn't an average (aka mean) current flow.

The poynting vector is basically E X H, and I don't think there's any way you're going to measure E without touching the wire, so you're stuck with measuring H. But, I think there is enough info in H to get to the answer.

Edit - I think that asodestrom has the real answer, though Change the question to 100 miles instead of 1, and then I'd start fishing through the backpack

 

Since the only limitations to the gear in the backpack are no GPS, I would take out my cell phone and call someone

 

i disagree about mean currents since the circuit is symmetrical, with the same current flowing back to the generator as away. Wasn't that from one of Kirkhoff's laws?


the real question seems to be, in a complete circuit, how can you tell the generator from the load just looking at the wires?

 

19mm sway bar for a stock suspension, 22 with stiffer springs and dampers. A 22 mm bar applied to stock springs and dampers, the car may rotate a bit more quickly than you may like. Sway bars and spring/damper rates need to be carefully matched. The bar is selected based on the spring and damping rates as a measure of FINE tuning the set-up. Springs, then dampers, then sway bars, that's the order...unless you prefer to be surprised by snap-oversteer.

I would walk the mile or two in either direction, knowing that I would have a 50/50 chance of being correct the first time.

...frame of reference is important...like being in a moving elevator without windows. Only way to tell, after the acceleration curve is finished - constant speed, what/where the force is, is to drop a coin or some other object...suddenly I realized I entered a room full of physicists...everything appeared normal...until everyone and every object slammed into one wall. Thats when everything suddenly stopped. Relatively...speaking.

I'm not even close to being a physicist, just having a bit of fun. I do like this stuff.

 

I think you should grab an EM book and look up transmission lines. They DO produce an EM field, even if there is a ground line near them. Since the return current isn't driving any real power, I don't think it would radiate much. If it's a coax or something that shields the field, that's a different problem - but afaik, that is not how power is transmitted anyhow.

I don't think it's practical to use an antenna to measure the E field, since at 60hz, the wavelength is VERY long. I'm no antenna expert, but I don't think you'll detect a 60hz signal in the air with anything that would fit in a backpack ... So I'm fairly sure you'd be stuck measuring the magnetic field and figuring out the direction of power flow from there.

 

if it were a two wire AC circuit, the current in each wire would be the same, just in opposed directions. If it were only one wire (separated in space a lot from the return wire) you would definitely get an EMF radiating from the wire like an antenna. But how would that tell you which end the load is on?

 

I know nothing, and care less about electricity, unless of course I'm in danger of being struck by lightning. Then, and only then do I stand at attention with great respect for the potential for electrons to move ever rapidly thru my flesh. However, I wonder if the driection of water, like electricity moving thru a conduit can be determined; consider a closed loop with a feed (from a 'T') at 12 0'Clock along with one valve in the loop at 6 O'Clock. Now, if the valve were equidistant from the feed, water would in theory flow equally in two directions making it very difficult to determine where the source is (assuming all else equal and that you do not know where the source is). But, as soon as we move the valve closer to the source, lets say to 9 O'Clock, flow- psi to be more exact- from 12 to 9 should be, no will be, greater because because the distance is shorter. I would think the same is true for electrons moving thru a conduit; pick three points, a left, a middle, and a right. Measure resistance in the middle first, then either left or right. Which ever is greater - left or right, is the direction of the source. Unless you are smack in the middle of a loop...is this done with electricity?

How'd we get here from a lifting rear inside tire? Amazing, how much can be described by physics.

 

And the difference is excellent. I'm still learning the handling of the car, as I've only had the plates on for about a week. But so far, I like the difference a lot. I don't know when I'll get out on the track, but the plates make a big difference in balence.

The RDRs do affect ride height. They seem to be best with ajustable height coil overs.

Matt

 

Alfa GTa. Notorious inside front wheel lifter. Dominated touring car racing in it's day.


If you happen to have one of these sitting in your barn, I'd be glad to take it off your hands.

 

To increase you chances of guessing right the first time, walk downhill. Power plants are usually situated close to a large body of water, from which they draw coolant. Such bodies of water are most often found at low elevations, relative to the surrounding topography. As a corollary to this, one can also look for steam clouds rising from cooling towers.

People in California near the windmill farms may, however, need to reverse this logic. Walk uphill, toward the crest of the hill.

 

Obviously not a physicist! They would all be dead because they could'nt stop equating variables before they starved to death!

Tire lifting- front wheel drive, short wheel base, stiff body, good tires, hard cornering (Its not necessary to do the math <its what they do!>

To eliminate this perceived problem, slow down or use crappy tires.

This thread is great. You all are nuts!