Interesting Definition and 790 Threads

I'd purchased a http://en.wikipedia.org/wiki/Mosquito_bat" recently. These things are very handy for swatting mosquitoes in the rainy season. A little while ago, I noticed something curious while swatting: after I hit the creature, it falls on the floor and begins to spin rapidly. Many a time I...

There is a popular myth that after drinking a bottle of water, the last bit is mostly backwash. Well I decided to try and test it, but got stumped. Lets call y the amount of backwash in the bottle Lets call x the number of sips taken The volume of the bottle will be 1000mL Assume each...

Hello, Chemistry grad student here about to start a physics-y project...so trying to learn about condensed matter physics. I get how screening works when you add a single charge to a gas of electrons, but what happens in a metal when you have a whole lattice, ie, a background charge density...

Draw a cylinder, with diameter D and length/height infinity, mark the top point Y and the bottom point Z Now Say a person falls into this cylinder/hole. (there are equal sources of light emitting into each end of the tube) From the falling person's perspective the point Z looks like an...

its from mensas website so it can't be too bad. i was just curious how you guys would do. i made sure to keep my time down to 30 minutes (although i did it in 32 minutes). i got a 20/30 on it which apparently is good enough to pass the real test... just thought id share it with you guys, since...

Hey there, I have to make a presentation about a technical topic in my technical spanish class. Since I have to hold the presentation in spanish and the listeners aren't experts either, I would like to choose an interesting topic which does not include too much jargon. I was considering...

So I've been working on this for a while now, but I'm a little stuck. I think I see how to solve the problem below, just need a couple tips to get me over the hurdle. Homework Statement There are two infinite wires in the same plane as a rectangular loop. Geometries are displayed in the...

Well I have been teaching my self mathematics for about 4 months now. Started with pre-algebra now I'm on "modern algebra". Thing is I haven't taken geometry in high-school(and will not be able to). So I'm looking for a quick book that is interesting enough to keep me well, interested. I know...

I and a few other freshman are in a seminar that's intended to help us in E & M and requires us to bring questions and problems to the seminar to work on. We've been doing some textbook problems, but it would be better if we could find something more challenging or conceptually interesting so...

Homework Statement I recently was given an interesting problem I thought I'd share with the community here. It's a fun exercise in mathematics. Given the equation: Po/P = [1+((k-1)/2)*Ma^2]^(k/(k-1)) From this stagnation ratio, derive the Bernoulli Equation: Po = P + 1/2 * rho * V^2...

Homework Statement http://www.kent.k12.wa.us/pcpow/questions/calc/0401trickortreat/index.html This is an old problem, and I have been able to solve one and two, I believe the answers are 1. pi cm/second 2. 50(pi) cm^3/second 3. This is the one I am not sure of. How can I solve...

A colleague of mine noticed that samples from a lognormal distribution seem to have much smaller kurtosis than the theoretical value - for example with \sigma=2 the theoretical value is about 9,000,000 whereas for samples of size N=1000 we found that the sample kurtosis averages around 280 and...

Homework Statement A person throws a ball off a roof that is 8 meters high with an angle of 45 degrees from the positive x axis. The ball is supposed to land in the center of a square that is centered 9 meters away from the base of the roof. With which initial velocity must the person throw...

Ok so here is a brainteaser, you should get it in your second attempt at the max., else consider yourself poor at math :biggrin: An ant is in one corner of a cube shaped room. (say one of the bottom corners on the floor). The ant decides to go to the opposite corner on the roof, which would...

Hi everybody, On a probability theory lecture I met an interesting problem: Let f : [0;1] -> R a bounded, 3 times continously differentiable function. Calculate the following limit n * \int_0^1 \int_0^1 ... \int_0^1 f(\frac{x_1+...+x_n}n)-f(0.5) dx_1...dx_n while n -> infinity Any ideas?

Hallow I want to know why if I throw 2 balls and one ball is bigger and whit more mass Why the two balls arrive to the ground in the same time This is the experiment of glilio glili Also I search after more experiment in mechanics (physics) like this Or like this experiment - if I throw a...

Homework Statement Let x=(1,0,0) y=(2,1,0) and z=(2,2,1) be column vectors in R3. Consider the set V={tx+sy+uz 0\leqt,s,u\leq1}. What does this look like specifically? Homework Equations n/a The Attempt at a Solution No work here, just a thinking problem, but I thought that...

I would have thought this standard crackpottery, but evidently it won "Best New Paper" from the University of Liege in Belgium! What do you all think? http://www.theresonanceproject.org/pdf/schwarzschild_proton_a4.pdf I can't find anything about the "quantum vacuum density" he talks...

http://www.sciencedaily.com/releases/2009/08/090811143716.htm Water is familiar to everyone—it shapes our bodies and our planet. But despite this abundance, the molecular structure of water has remained a mystery, with the substance exhibiting many strange properties that are still poorly...

Homework Statement At the top of a pole vault, an athlete actually can do work pushing on the pole before releasing it. Suppose the pushing force that the pole exerts back on the athlete is given by F(x) = (160N/M )x - (180n/m^2 )x^2 acting over a distance of 0.24m. How much work is done...

What are in your opinion the most interesting areas or topics in foundational physics? (that have or could have profound philosophical implications) I want to see what's out there.

Little Tyke [my office cat] came into the office and started making a lot of noise knocking about. Then I realized why: She had brought in a snake that was close to a four-feet long! Cripes! After fighting to keep her away and finally managing to catch the snake by grabbing the tail, as I was...

Found this on the door to a bathroom stall at work. I thought it was interesting to see a literary reference in a graffito. Perhaps "Screwtape" has some other significance to the author other than the book by C.S. Lewis though. Does anyone else have interesting graffiti to share?

I'm a normal adult male (abt 6ft tall, 180 pounds), if my density was that of the mean density of the universe, what would be my volume?

What area of Electrical Engineering is most interesting with respect to research/specialization? I heard from somewhere it's Telecommunication. any suggestions?

Very Interesting Question on Division of Polynomials! [b]1. Question: 'When a polynomial f(x)= x^4 - 6x^3 + 16x^2 - 25x + 10 is divided by another polynomiall g(x)= x^2 - 2x + k, the remainder is x+a. Find the value of a k and a'. Homework Equations [b]3. I tried solving it by...

I caught this in the NY Times: http://community.nytimes.com/comments/www.nytimes.com/2009/06/28/health/research/28cancer.html?sort=oldest&offset=4 The article focuses on cancer research, but the conclusions can be applied to all medical research. As the article correctly pointed out...

Tom.stoer recently started a thread to collect ideas on the topic of stringy dislike of LQG. I thought that was a constructive initiative. At least for me it was helpful to sample what are the current rationales of dismissal, in part because this is a kind of folklore that has changed over time...

Homework Statement Let U be a fixed nxn matrix, and consider the operator T:Msub(n,n)---->Msub(n,n) given by T(A)=UA (look familiar?:biggrin:) Show that if dim[Esub(c)(U)]=d then dim[Esub(c)(T)]=nd. Homework Equations The Attempt at a Solution The author provided a small hint. He suggested...

Hello, again! I got one very interesting question. We got three archers, and the probability of the ones to hit the target is: A1, A2, A3. What if the task is to find the probability that the target will be hit at least from one archer. So at least one archer to hit the target. Is it P(A1 U...

What will be the most interesting improvement in technology? I like to read up on new advances in science and often read about fantastic predictions in science. For example, in the world of television: http://www.sciencedaily.com/releases/2008/10/081002084217.htm"...

Homework Statement You ask your friend if the football is on 9pm or 10pm. He sometimes tells the truth and sometimes doesn't. What should you ask him so that you will be certain which time the football will be on? The Attempt at a Solution ASK: Is it true that 'You are telling the truth...

I enjoy learning new things every time I do a problem set. Take the wheatstone bridge for example. Upon my initial observation, I concluded that the total upper electric potential(V1 + V2) minus the lower electric potential(V3 + V4) ought to give the electric potential that exists across the...

I have to do a presentation on atomic theory and periodic table. What are the interesting points I can include to my presentation? Thanks in advance!

Homework Statement This week’s physics puzzle is a classic often used in mechanics. A point-like marble of mass m is situated on top of an immobile hemisphere of radius R. It is given a tiny push and starts rolling down. At what angle θ will it detach from the hemisphere’s surface and fly...

Allright call me a naturalist , for those of you interested I had a short encounter with mother nature the other day. Friday afternoon - I found a starling bird in my front lawn , it was being real still with its head pointed to the sky. It started to hop in the other direction as soon as it...

Peugeot have a new hybrid 4x4 They took a regular front wheel drive car and added an electric motor driving the rear wheels only. It can run ICE + front wheel only for freeways without the extra drag of permanent 4wd Electric rear wheel only for in-town/traffic low speed, or Diesel front +...

We are to find a scientific argument and either prove it or debunk it through research. This was an introductory Physics class and he would prefer to stay somewhat within the scope of the class. Does anybody have interesting debunk-ings?

Homework Statement Evaluate the integral, (x^2+3x-8/x^2+16)dx, without using partial fraction expansion. Now this has really confused me. I know that partial fraction expansion is not viable because the mumerator has a higher power overall than the denominator The Attempt at a Solution...

Hi, first I want to apologize for my english. I'm not from an English speaking country and I have to practise. I have a quite interesting physical assignment for you. I was trying but I still can't solve it. If you would have an idea or if you would know how to solve it please let me...

Homework Statement There Are two bodies with mases M1 and M2 placed in space separated by a distance D. They attract each other due to gravitational forces and hence acclerate towards each other.The problem is to Find out the time taken before their collision? Homework Equations I know...

I have spent a long time stuggling with an interesting problem which was set up by my brother some time ago: Consider an object that starts moving along the line according to the equation below: v(s)=1+{s}^{2} where s is the total distance traveled by the object and v is the velocity of the...

Some of you may have heard this before, but its one of those classic problem that I love debating, so please weigh in if you think you have the answer... You have an S-shaped sprinkler, when water is run out of it the sprinkler rotates about its center axis in the opposite direction to the...

There is a cunducting hollow sphere. We know if we charge it all the charges will stay at the outer surface. But if we drill a hole of radius r(say) then what fraction of the charge will remain inside and outside surface I think it is logical to think that less charge will stay in the...

Hi all, I have a presentation for my engineering-based public speaking class coming up. It must be technical in nature. I can't decide what would be easy enough for me to learn about while keeping it at a technical level and still interesting to my peers. I've been thinking about: A...

p is probability that a man will success in a single shot n is number of shots man is going to make 1)what is probability that a man will score at least one series of at least k successive successful shots (in the interval of n)? 2)what is probability that a difference between his...

i need help finding the limits above and below the branch cut segment of sqrt(z^2-1) for -1<x<1 I always get total phase above is pi/2 and total phase below is 3pi/2 but this is wrong please help

For everyone who watches dirty jobs (I'm guessing most of us) and everybody who works in an industry with health and safety policies (a lot of us). http://www.ted.com/index.php/talks/mike_rowe_celebrates_dirty_jobs.html I hadn't appreciated what a smart and interesting guy the presenter is

Hi all, I have a project to do for system of ordinal differential equations and their applications in physics. One of my tasks is to find where in physics the following system of ordinal differential equations appear: dA1(x)/dx=f(x).A2(x) dA2(x)/dx=f(x).A1(x)+ h(x).A2(x)+ g(x).A3(x)...

I found this on the web, it was written by someone without formal physics education but I was wondering what some educated users here with a background in physics think about it. My problem with it is that he claims time doesn't exist in any perspective only this physical continuity but how can...