Strange Definition and 566 Threads

Hello everyone, I have a really interesting question here. I am measuring the factor of friction between two different metals. My results are a beat cloudy. When I use Steel - Brass surfaces the factor of friction, μ is being reduced while I am increasing the applied force. In other side, when I...

Hello, I am having difficulty solving for the Area and wondering if this is correct.

Question http://gyazo.com/17223631de9dfcbcca00f6b3f8758cb9 I'm talking about part ii) if ## a = |\vec{BC}| ## then ## a^2 = (\vec{OC} - \vec{OB})^2 ## is this correct? if we expand a^2 then we get ## a^2 = (\vec{OC})^2 - 2\vec{OC}\vec{OB} + (\vec{OB})^2 ## I don't understand, what is...

I've been following a few derivations for quantities in classical mechanics of rotating systems, and one of the integrals is transformed in a way I've never seen before. For angle theta, angular velocity omega and angular acceleration alpha: Intuitively I can see that they've 'just' swapped...

I am using JAVA to generate a graph of the E field close to a conducting plane. The result which I want to graph is $$E_z (x)= \frac{Q}{2\pi \epsilon_o} \left(\frac{d}{(x^2+d^2)^{3/2}} - \frac{h}{(x^2+h^2)^{3/2}}\right).$$ The code is below: import java.io.Console; import java.io.*; import...

hello please see attached snapshot from the book of Ligthmann & al. (problem book in relativity and gravitation). Can somebody please explain the expression for the derivative of the solid angle ? here it is given as dvxdvy where the v's are speeds ! How come this is so ? Thanks,

Anyone have really weird or scary dreams?

Please look at the picture I uploaded. Can somebody explain to me how the author of my book can claim that the "vertical component of the ring surface-tension force at the interface in the tube balances the weight of the column of fluid of height h"? This stuff is weird. How can TENSION...

Homework Statement Show that for a square matrix the (i,j) entry is equlivant to the (j,i) entry in a symmetric matrix. Homework Equations The Attempt at a Solution I just felt this question was weird. They don't give the answers so I'm looking for confirmation. I guess...

Hello everybody, I was working on an electronics project, and one of the LEDs (actually I'm using only one) started acting really strange! It will light up when I come close to it, ONLY if I have been out of the room for some time! And that's not all, the period for which it will light...

The so called 'Moebious Function' is a discrete function defined as... $$\mu(n)= \begin{cases} - 1 &\text{if n has an odd number of prime distinct fators} \\ 0 &\text{if n has one or more prime fractors with exponent greater than one}\\ 1 &\text{if n has an even number of prime distinct...

I took the prime numbers from this link: http://nl.wikibooks.org/wiki/Wiskunde/Getallen/Lijst_priemgetallen I did take the first three lines I did the following with the numbers The prime 11 = 1+1 = 2 The prime 13 = 1+3 = 4 The prime 17 = 1+7 = 8 and so on This is the result for the...

So I was 3rd author of a paper published by our group. I then applied for a fellowship which requested me to describe my research activities. I cited the paper I had my name on. My advisor reviewed the application and told me to put my name first on the fellowship application. She even wrote...

Strange or bizarre covers of "Best Songs". Occasionally, one hears a rather strange, even bizarre cover, of an older "best song". That's what this thread is for. The idea is that if you find a strange, or incongruous cover of one of the songs in the "Best Songs Ever" thread, you can post it...

Hi, I did a search for "crackpot physics" and found https://www.physicsforums.com/showthread.php?t=111647 and then this forum. A friend of mine found some strange twins paradox on the net but he can't remember where. Neither of us can figure out the solution, but it must be crackpot...

material made from up and down quark but we have four more quark what they are do??

I have a bowl in my kitchen that turns black when heated (when it goes to the microwave oven or the washing machine). It is driving my crazy so I started to investigate. Here are the results: This is how it looks after cleaning it: After going to the microwave it becomes like this...

I noticed recently that I've been hearing people say something that sounds really clumsy and extremely grammatically incorrect. I've heard this many times before from different different people from different places, including the people on the news, and I heard someone say it last night when I...

Hello. So I've got an electrical circuit on page 4 of this: http://www.iuventa.sk/files/documents/2_olympiady/fo/54.%20rocnik%202012-2013/ulohy%20a%20riesenia/skolske%20kolo/f54skcul13.pdf and I am to calculate the total resistance of the circuit, but I have no idea on how to solve that strange...

What are some of the strangest vector spaces you know? I don't know many, but I like defining V over R as 1 tuples. Defining vector addition as field multiplication and scalar multiplication as field exponentiation. That one's always cool. Have any cool vector spaces? Maybe ones not over R but...

I am a bit wary about posting this, as I am pretty sure what the response would be if I claimed this was paranormal or some other weird stuff. So before we start, I do not believe in ghosts, I do not follow religion, I am very much a believer in the scientific method. I am not claiming to have...

Can someone identity what the issue here is before I throw my computer out the window. By the way, this just worked 10mins ago. I restarted Mathematica and my computer but it now insist z isn't an equation. ClearAll["Global`*"]; me = 5.974*10^(24); mm = 7.348*10^(22); G = 6.67259*10^(-20)...

Problem: Show that if $P(A_i)=1$ for all $i \ge 1$ then $P(\bigcap_{i=1}^{\infty}A_i)=1$. What is strange about this question is the first part, $P(A_i)=1$ for all $i \ge 1$. If I'm understanding this correctly that's saying that $P(A_1)=1$, $P(A_2)=1$...$P(A_n)=1$, for $n \ge i \ge 1$. This is...

Any idea what's going on here: http://www.sootoday.com/content/news/full_story.asp?StoryNumber=50683%20 Thanks...

Why do scholarships want these strange essays all the time? Is it just a deterrent to see who really wants the money? Are these things worth writing in mass? Because I can see applying for 10 scholarships with 10 essays as being very time consuming.

Every once in awhile you have a conversation with someone that leaves you shaking your head, right? Here is one from today. Me: I'd like to get my car serviced [make and model given, etc] Her: What do you need done? Me: My heater fan is failing intermittantly Her: Does it work at all? I need to...

Hi everybody, while doing a complex analysis exercise, i came to a strange inequality which i don't know how to interpretate. Suppose you have a sequence $\{a_j\}$ of positive real number. Let $\rho$ a positive real number. The inequality i found after some calculation is...

Hi we had this strange question come up in our advanced class and I'm quite confused as to how to go about figuring this one out. Here is the situation of a question A company sells boxes to its customers but recently the company has been struggling to make a profit. Looking at the plans they...

Hello everyone! I'm a 1st grade student in a slovenian high school. Recently, I've became very interested in numbers and math itsself. I was just playing around with a few numbers, when I came across a few that are unique. I was wondering which numbers can loop back to themselfes after this...

Twice now I have called someone from my landline and ended up eavesdropping [briefly] on the person I'm calling. They were on the phone when I called. But instead of getting a busy signal or voicemail, I ended up hearing one side of their ongoing conversation. In one case I knew I could hear the...

I dumped a bucket of water into my bathroom sink (nevermind why, that's a whole other can of worms), and afterwards my sink has started having problems. It hasn't been draining properly. I'll wash my hands and the water will stay in the sink not draining at all. Then I'll come back later and the...

It was this summer, in the morning, I was going down the hill to a river, through a sort of meadow, and noticed that everywhere I looked grass was covered with spider webs. I think it was mostly dry-ish tall grass with a... structure capable of supporting a web (don't know what it's called, but...

Hello everyone, I was reading a physics book and found an exercise. This time I faced with a really strange one! I can't find out what I am doing wrong! I am really good at physics and math, but sometimes I fail as many people do... :smile: The answer in the book says ~0.4m, but I am unable to...

Homework Statement I was given a DE of the form: \Phi^{''}+(6/\eta)\Phi^{'}=0 where the next step was given as \Phi^{'} \propto \eta^{-6} where the answer came out to be \Phi \propto \eta^{-5} + constant The Attempt at a Solution My attempt was to set \Phi^{'}=x where I would then get...

Hi, Consider the real variable x and some real constant x_{0}. I want to integrate \int_{-\infty}^{\infty}\frac{x_{0}}{x_{0}-x} This blows up when the denominator is zero but we can still take the principal value of the integral. That is, we notice that the integral is an odd function around...

What does the right arrow mean in this context: " ...Then the process t \mapsto \int_{0}^t \phi_s dM_s are well-defined continuous local martingales, whose quadratic variations are given by ... " Is this supposed to mean "the process X that is the mapping X: t \mapsto \int_{0}^t \phi_s dM_s"

Hi, I am trying to compile a code that should work fine, but I am getting errors and also some odd characters are printing on the screen. This is the output: ENTER INPUT FILE NAME (INCLUDE EXTENSION NAME) blisw.inp YOUR INPUT FILE IS blisw.inp...

Homework Statement A ball is thrown upward from a building 30 meters tall and misses the edge on its way down, hitting the ground 6 seconds after it was thrown. A) With what speed was it thrown? B) What is its highest height?Homework Equations Vf = Vi + at x = 1/2(Vi + Vf) x = Vi t + 1/2(at^2)...

Homework Statement f(x) is an injective function (1 to 1) and continuous in [a, b], and f(a) < f(b). Show that the range of f is the interval [f(a), f(b)] Homework Equations Intermediate Value Theorem The Attempt at a Solution We are asked to use the intermediate value theorem to...

So I was playing with a USB microscope at my desk, and I just viewed a Subway napkin with it. Attached is the picture I saw at ~75x magnification There's dots of all sorts of colors.. yellow, light blue, green, red.. even pink. Does anyone know what the colored dots might be? There's a...

Hi guys, I have a question when solving 3D Helmholtz equation derived from Maxwell equations. Normally I will get a plane wave solution. But when I used the method of separation variables for the three components Ex Ey and Ez, I found that the vector k in these three can be different as long...

I have a simple iteration program that does something I can't explain. It has to do with the use of if then statements. I can't see why this change would change the outcome. Here are the 2 examples: This works: if (guess.eq.target) then lp=3 write (*,*)...

Generally I am on the Physics Forum, but I got my hands on a good microscope a while back and decided to grow some little dudes to look at. My third incubation batch consisted of filtered drinking water and a bit of stuff from my mulch pile. Grew a few interesting little guys and looked them...

Calculus Integration from -10 to 0 Yields a Strange Result [RESOLVED] As part of a far greater enquiry, I found myself integrating: \int^{0}_{-10}x^3+2dx So, I began integrating the x^3+2 component, yielding the result of: [\frac{x^4}{4}+2x]^{0}_{-10} Which can then be set out as a...

I'm confused by Mathematica's behaviour when plotting some functions I've constructed by interpolating functions. I have three graphs (attached). The first is a plot of the family of functions; they're negative, and decreasing to zero. I tried to do a LogLogPlot to look at their behaviour as...

Homework Statement We are given a function defined by x = uv, y = 1/2 (u^2-v^2)Homework Equations I derived the line element ds^2 = (u^2+v^2) dv^2 + (u^2+v^2) du^2 However I decided this was to unwieldy to derive our circumference where C = 2*{R}\oint_{-R}^{R} ds So I decided to try to...

I have a friend who has this strange condition. While eating rice, twice so far, the rice sort of blocks his throat near the centre of his chest. Now, he doesn't have difficulty breathing but he keeps getting tiny hiccups for about 8-15 minutes. The whole while he feels a sort of pain resembling...

Hi, I have seen a couple of videos on youtube where people simply hook a homemade simple coil of copper wire directly to the House 120v AC. One of them for example hooked a close wound aircore coil with 14 gage wire(01.6mm), 6"(152mm)diameter, about 1" length and 30 turns only.. and...

Hallo, I tried to use 'finite difference' method to solve a Initial Value Problem(IVP). For the two boundaries I used periodical condtion and for the differential operators I used 4th degree center approximations. But as result, I got this thing. Where comes this strange oscillation What do you...

Well, the thing is that since one year or more I'm trying to find a non toxic compound that can be done mixing water with "something", I need that the result of that has "like gum" properties, or a high density foam (like a hard mattress). I don't know much about chemistry but I think there must...