Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
6 online now:
Newest Member: popoi
Post Volume: Total: 915,817 Year: 3,074/9,624 Month: 919/1,588 Week: 102/223 Day: 13/17 Hour: 0/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Using your common sense to solve a physics problem.
coffee_addict
Member (Idle past 477 days)
Posts: 3645
From: Indianapolis, IN
Joined: 03-29-2004


Message 121 of 188 (144960)
09-27-2004 12:58 AM


I was just talking to a friend... not really a friend but more like someone that I just met in the hall way... about physics and stuff. I had a lot of free time, so we talked for quite some time. It turned out that he didn't really know that there are physics problems that deal with stuff much more complicated than the ones we see in kinematics. He didn't really know that there are problems such as the ones dealing with electromagnetism where it's entirely calculus based. With kinematics, you can pretty much get away with only basic knowledge of algebra. However, it gets a lot more complicated than that in higher disciplines of physics.
This got me thinking. If the rat (please don't take offense in me calling you the rat, I tend to do that with people... like the frog) thought that common sense alone could give you enough skill to solve such a problem as a car breaking to stop, it crossed my mind that may be there are members on this board that are still under the impression that physics is only about solving algebraic equations and dealing with everyday stuff.
So, here is a slightly more difficult problem just so you wouldn't think that physicists are fruitcakes. No, I don't really expect any non-physicist to be able to solve this. It's relatively simple, but it's quite beyond everyday common sense, I'd say.
Find the electric field a distance z above one end of a straight line segment of length L, which carries a uniform line charge of λ. What happens if z is approaching infinity?
Here is the equation necessary for this problem.
E = 1 / (4 * pi * ε) ∫ [(λ r')/R2] * R^ dl'
where E = elctric field, ε = permitivity constant, r' = field point, R = distance between a source charge point on the line segment and the field point r', and R^ is the direction of the magnitude.
Here is a picture to make it easier.
As I know it, there are 2 ways to do this. One of them will take you 2 pages to do, and the other will take you about 4 or 5 steps. Not supprisingly, I still have trouble when doing the long way because it's too complicated.
Have fun.

The Laminator
For goodness's sake, please vote Democrat this November!

Replies to this message:
 Message 123 by riVeRraT, posted 09-27-2004 3:58 PM coffee_addict has replied
 Message 124 by riVeRraT, posted 09-27-2004 4:01 PM coffee_addict has not replied

Rei
Member (Idle past 7013 days)
Posts: 1546
From: Iowa City, IA
Joined: 09-03-2003


Message 122 of 188 (145086)
09-27-2004 2:24 PM
Reply to: Message 111 by riVeRraT
09-25-2004 11:53 AM


I don't care if you would have suggested that change; that is completely off topic. You were asked for the rammifications of a proposed change. You pointed only to minor rammifications, and completely ignored the major ones (which led to collapse). You completely failed, where a mathematical analysis would easily have succeeded.
This message has been edited by Rei, 09-27-2004 01:25 PM

"Illuminant light,
illuminate me."

This message is a reply to:
 Message 111 by riVeRraT, posted 09-25-2004 11:53 AM riVeRraT has not replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 123 of 188 (145110)
09-27-2004 3:58 PM
Reply to: Message 121 by coffee_addict
09-27-2004 12:58 AM


Please lam, I never said jerk physists.
I also never meant all scientists.
I am so intrigued by magnetism. I really wish I could go to college and learn more about it. I just don't have the time. I also don't have the time to finish the first problem, but I promise I will. I will also consider trying to at least understand this problem as well.
When dealing with common sense, I fully realize that common sense can get you in trouble. Common sense does not also mean that you can figure something out in a day or a week, or whatever, but that you can indeed one day figure it out. Regardless of your training. Those who recieve training and pocess common sense, will figure things out much easier, and see things more clearly.
Tell me, do you think just because you can figure this out on paper, means that you can see whats going on? You might, but what about the next guy?
Isn't there a big difference between being taught formulas, and trying to figure them out on your own?

This message is a reply to:
 Message 121 by coffee_addict, posted 09-27-2004 12:58 AM coffee_addict has replied

Replies to this message:
 Message 127 by coffee_addict, posted 09-27-2004 7:21 PM riVeRraT has replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 124 of 188 (145111)
09-27-2004 4:01 PM
Reply to: Message 121 by coffee_addict
09-27-2004 12:58 AM


What is λ ?

This message is a reply to:
 Message 121 by coffee_addict, posted 09-27-2004 12:58 AM coffee_addict has not replied

Replies to this message:
 Message 125 by Percy, posted 09-27-2004 5:47 PM riVeRraT has replied
 Message 126 by Melchior, posted 09-27-2004 6:04 PM riVeRraT has not replied

Percy
Member
Posts: 22392
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.3


Message 125 of 188 (145143)
09-27-2004 5:47 PM
Reply to: Message 124 by riVeRraT
09-27-2004 4:01 PM


Lamba usually refers to wavelength.
--Percy

This message is a reply to:
 Message 124 by riVeRraT, posted 09-27-2004 4:01 PM riVeRraT has replied

Replies to this message:
 Message 131 by riVeRraT, posted 09-28-2004 8:50 AM Percy has not replied

Melchior
Inactive Member


Message 126 of 188 (145145)
09-27-2004 6:04 PM
Reply to: Message 124 by riVeRraT
09-27-2004 4:01 PM


quote:
which carries a uniform line charge of λ.
Lambda is a rather frequent symbol and you can't really assume it means wavelenght unless you are talking about wave-physics or similar fields.
This message has been edited by Melchior, 09-27-2004 05:04 PM

This message is a reply to:
 Message 124 by riVeRraT, posted 09-27-2004 4:01 PM riVeRraT has not replied

coffee_addict
Member (Idle past 477 days)
Posts: 3645
From: Indianapolis, IN
Joined: 03-29-2004


Message 127 of 188 (145156)
09-27-2004 7:21 PM
Reply to: Message 123 by riVeRraT
09-27-2004 3:58 PM


Lam writes:
Find the electric field a distance z above one end of a straight line segment of length L, which carries a uniform line charge of λ. What happens if z is approaching infinity?
In other words, lambda in this case is the uniform line charge.
the rat writes:
Tell me, do you think just because you can figure this out on paper, means that you can see whats going on? You might, but what about the next guy?
Yes, I do really see what's going on. One of the most wildly misconceptions regarding physics is that physicists can't really understand what the equations are saying. That is not true.
The average person might not know what the equations are saying, but if you are studying physics you better know damn well what the equations are saying.
Isn't there a big difference between being taught formulas, and trying to figure them out on your own?
Actually, I did figure out that equation on my own. The only reason I posted it here is because I didn't expect non-physicists to be able to. It's like me writing a paper on economics... I wouldn't know where to begin.
Again, if you are studying physics and you can't derive this equation on your own, then you have a problem.
This message has been edited by Lam, 09-27-2004 06:22 PM

The Laminator
For goodness's sake, please vote Democrat this November!

This message is a reply to:
 Message 123 by riVeRraT, posted 09-27-2004 3:58 PM riVeRraT has replied

Replies to this message:
 Message 132 by riVeRraT, posted 09-28-2004 8:58 AM coffee_addict has not replied

tsig
Member (Idle past 2909 days)
Posts: 738
From: USA
Joined: 04-09-2004


Message 128 of 188 (145158)
09-27-2004 7:38 PM
Reply to: Message 118 by riVeRraT
09-26-2004 8:45 AM


Nonresponse
Riverrat
You did not respond to the content of my post.

This message is a reply to:
 Message 118 by riVeRraT, posted 09-26-2004 8:45 AM riVeRraT has replied

Replies to this message:
 Message 129 by coffee_addict, posted 09-27-2004 7:48 PM tsig has replied
 Message 133 by riVeRraT, posted 09-28-2004 9:00 AM tsig has replied

coffee_addict
Member (Idle past 477 days)
Posts: 3645
From: Indianapolis, IN
Joined: 03-29-2004


Message 129 of 188 (145161)
09-27-2004 7:48 PM
Reply to: Message 128 by tsig
09-27-2004 7:38 PM


Re: Nonresponse
Observer writes:
Riverrat
You did not respond to the content of my post.
I'm going to say something for the rat, if I may. I think the rat was talking about egoistic engineers who think that they know everything better than the mechanics who usually deal with these things hands on. Although I am not a big fan of the rat (since he hates people like me), I think that there is some merit to the rat's point.
I've met some freshed out of college know-it-all engineers, and one of them was my brother. However, I've also encountered some know-it-all mechanics in my lifetime *ahem*.

The Laminator
For goodness's sake, please vote Democrat this November!

This message is a reply to:
 Message 128 by tsig, posted 09-27-2004 7:38 PM tsig has replied

Replies to this message:
 Message 130 by tsig, posted 09-27-2004 9:39 PM coffee_addict has not replied
 Message 134 by riVeRraT, posted 09-28-2004 9:07 AM coffee_addict has not replied

tsig
Member (Idle past 2909 days)
Posts: 738
From: USA
Joined: 04-09-2004


Message 130 of 188 (145183)
09-27-2004 9:39 PM
Reply to: Message 129 by coffee_addict
09-27-2004 7:48 PM


Re: Nonresponse
Why defend the rat? He said that common sense was enough to solve any problem then proved unable to understand the problem presented to him.

This message is a reply to:
 Message 129 by coffee_addict, posted 09-27-2004 7:48 PM coffee_addict has not replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 131 of 188 (145316)
09-28-2004 8:50 AM
Reply to: Message 125 by Percy
09-27-2004 5:47 PM


Crap, I knew that too. If you don't do this everyday you forget. I learned that through studying ametuer radio. ok.

This message is a reply to:
 Message 125 by Percy, posted 09-27-2004 5:47 PM Percy has not replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 132 of 188 (145318)
09-28-2004 8:58 AM
Reply to: Message 127 by coffee_addict
09-27-2004 7:21 PM


Yes, I do really see what's going on. One of the most wildly misconceptions regarding physics is that physicists can't really understand what the equations are saying. That is not true.
I figured you knew. You would be interested in a little project I am working on here. I trying to design a more effiecient electric motor.
I could probably use your knowledge to help me figure it out. But I think I am getting it anyway.

This message is a reply to:
 Message 127 by coffee_addict, posted 09-27-2004 7:21 PM coffee_addict has not replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 133 of 188 (145320)
09-28-2004 9:00 AM
Reply to: Message 128 by tsig
09-27-2004 7:38 PM


Re: Nonresponse
You are beating a dead horse, give it up already.

This message is a reply to:
 Message 128 by tsig, posted 09-27-2004 7:38 PM tsig has replied

Replies to this message:
 Message 135 by Ooook!, posted 09-28-2004 9:40 AM riVeRraT has replied
 Message 148 by tsig, posted 09-28-2004 8:49 PM riVeRraT has not replied

riVeRraT
Member (Idle past 416 days)
Posts: 5788
From: NY USA
Joined: 05-09-2004


Message 134 of 188 (145321)
09-28-2004 9:07 AM
Reply to: Message 129 by coffee_addict
09-27-2004 7:48 PM


Re: Nonresponse
I don't hate you Lam. I love you.
I also like you. I have stated before, that I respect what you have to say, because your posts make sense. We just don't agree on believing in God. If we knew each other outside this forum, in the real world, we would get along.
I argue things sometimes to get the truth out.
I came into this forum, to preach the gospel, not knowing how really smart some of you are. It has been a great lesson for me. Its been great to discuss with you.

This message is a reply to:
 Message 129 by coffee_addict, posted 09-27-2004 7:48 PM coffee_addict has not replied

Ooook!
Member (Idle past 5815 days)
Posts: 340
From: London, UK
Joined: 09-29-2003


Message 135 of 188 (145323)
09-28-2004 9:40 AM
Reply to: Message 133 by riVeRraT
09-28-2004 9:00 AM


Re: Nonresponse
You are beating a dead horse, give it up already.
I know this is a bit of a cheeky/lazy way of going about things, but can you point out the post in which you first used the term 'jerk scientist' (I've done a bit of a search and can't find it). It might be interesting to see the initial context of the comment and whether you've softened your stance after it had the desired inflammatory effect.
Cheers

This message is a reply to:
 Message 133 by riVeRraT, posted 09-28-2004 9:00 AM riVeRraT has replied

Replies to this message:
 Message 136 by PaulK, posted 09-28-2004 9:58 AM Ooook! has not replied
 Message 138 by riVeRraT, posted 09-28-2004 10:15 AM Ooook! has replied

Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024