Mystery Definition and 913 Threads

In our apartment, for the last few months, my wife and I are being puzzled by strange sounds coming from the dining area while we remain in the bedroom at night. The first time we heard, I was quiet. Then my wife said, "Did you hear that?" So, it was no hallucination whatsoever. It is a distinct...

Hi everyone, I am a bit confused about the Penrose Process. Let's say a particle with energy E at infinity arrives in the ergoregion of a Kerr black hole and then it decays into two photons. One of them has L_1<0 and E_1<0 and hence it falls towards the singularity, while the other has L_2>0...

Hi everyone! As we all know standing wave of 2 fixed ends formed by the combination of coming wave and reflection wave. But I wonder why there still have a reflection wave combinating with coming wave to form standing wave of 2 free ends? Many thanks.

I am a big Star Wars fan and I was just wondering what would happen if two Star Destroyers collided during lightspeed? could it be possible to go so fast you could go through something without destroying it?

Can you explain this?

Could someone please explain how they're getting the answers in the table, for example $g = (123)$.

I'm reading about the interesting data that suggests a new heavy particle about 750 GeV. It talks about the energy being the mass times the velocity of light squared and is indicated by the two photons as the particles decay. I guess it's the same with this and a nuclear explosion which...

Homework Statement So I have to plot 2 sets of IV curves for my lab and find the operating points of where they cross. Problem is, they don't cross! I'm not sure if this is the right place to ask, but my professor isn't responding to my emails so here it is. This is what the circuit looks...

Homework Statement A guitar player is plucking a strong of length 30cm. How fast must the player move towards or away from the stationary observer, in order for the observer to mistake the fundamental frequency for the second harmonic? ANSWER: 2(Vsound) towards the observer Homework...

How is the photon torpedo supposed to work?

It appears that black holes do exist in our universe, in the sense that there are objects so massive and so small that there must be an event horizon. Is it generally accepted that there is "really" a singularity inside these event horizons, or that we just don't know, and may never know?

Homework Statement When a problem says 76 moles of P4O10 contains how many moles of P. I can't seem to see why 76 moles of this molecule would contain more moles in it. Homework EquationsThe Attempt at a Solution I know the answer is 76 moles of P = 76 * 4 but how could a compound P4O10 that...

Hi, Every year, my youth group goes on a summer trip, the location of which is kept a complete secret from us until a certain deadline. Before the deadline, our leaders usually give us a riddle to the location of our trip. Specifically, one of our leaders, who has a degree in Physics from the...

Homework Statement An airplane with a mass of 5.32 x 10^4 Kg accelerates down the runway at 1.76 m/s^2 [forward]. Calculate the net force acting on the airplane. Homework Equations Fnet=ma The Attempt at a Solution I did this by multiplying the two given values, but my answer was 93632N...

So we have this pepper shaker made of glass with a print on it. One fine dinner, it ran out of pepper, so I opened the lid to fill it in and noticed a peculiar thing – small particles of pepper dust were stuck to the inside glass walls but only in places, where the print wasn’t present on...

Today's APOD http://apod.nasa.gov/apod/ap160125.html Shows this fascinating table. What a pity that is doesn't show isotopes. Strange are Ba, La, Ce which are shown as large star but not supernova. The article says that the origin of Cu is not well known. Fascinating. I'm curious about the...

Hi I want to know whether DNA inside our brain neuron cells helps us process images of what we see through our eyes.

Hello everyone, I have a question regarding a formula which can be derived from conservation of momentum and energy in the Compton effect. From conservation of momentum and energy during the collision of a photon with an electron, it is possible to get two expressions for the final energy E of...

Radiation dominated the universe 4,700yrs to 378,000yrs, do the facts in the literature mean there was no baryonic matter between those yrs or was there still plasma or some sort of mass?

Hello everyone. The title of my question may look a bit silly, but I think it is quite interesting. Before a couple of days, my aunt told me that she found a paint? for her nails, which had the following feature: her nails would have a specific color when she was in her house and a different...

Hello, In the picture above a couple are shown with their children. Or are they actually their children? Is it possible for them, having green (?) and hazel (?) eyes, to get 1 child with blue eyes and 3 children with brown eyes?

An official kickstarter campaign has been made! I remember watching this show as a kid and crying laughing so hard! https://www.kickstarter.com/projects/mst3k/bringbackmst3k

Homework Statement Homework Equations My assumption:- if one of the ropes have been cut, it mean the object just hang VERTICALLY with one rope with 5N load on it.Is it my assumption is correct? The Attempt at a Solution Tension of the other rope = 5N (is it correct)?? base on my assumption...

I know heat as the average kinetic energy of the particles in a system, is this correct? And that heat is transferred by transferring energy, which causes particles to go slower/faster, is this correct? But what exactly is heat? Is heat made up of smaller particles, such as light is photons? I...

hey guys,Entropy is supposed to be a measure of disorder in a a system then why is the formula ∫dQ/T used.I can understand why entropy increases with the energy in the system but why is the absolute temperature of the system relevent, is it a proportionality constant ? please enligthen me on...

That's the title of the NASA press release (I added the date). 8 a.m. PDT = 3 p.m. UCT = 5 p.m. CEST (Central European Summer Time) The panel includes an expert for the HiRISE experiment, a high-resolution telescope in Mars orbit. Whatever they have, apparently images of some area are highly...

How did we know that our galaxy is spiral?!

What does 'high spin' mean? I have heard of mono atomic gold having unusual properties. What is going on inside the atom?

So, I am kind of learning QM on my own, and through my chemistry book. It doesn't explain any further than the shapes of orbitals, and I am wondering did anyone found out why is space in the orbitals between the clusters of probability blank.

Hi, I imagined this device and I don't understand where is the error. I posted here because it's a simple mechanical device, I have trouble with the sum of torque. The potential energy must be constant. I think I forgot a torque, if you see where ? A torus turns counterclockwise around the...

Homework Statement First question of this particular page http://www.hourlybook.com/ncert-questions-pmts-cell-cycle-cell-division/ Homework Equations the answer is given as C. The Attempt at a Solution But i didn't understand because in last phase i.e D dna content is again reduced to 2c.But...

I was watching 'The sound of Music' for the nth time with my 11 year old daughter. There is a scene at the beginning, the Reverend mother tells Maria to go to the Captain's house. My daughter insists the reverend mother says "the captain's wife died seven years ago". And when the kids's names...

Hello, I've worked through most of Carroll's appendix on the non-coordinate basis. I see and agree how the spin connection and tetrad one-forms are useful while calculating. However as an example he sets out to apply the formalism to a spatially flat, expanding universe. ds^2 = -dt^2...

As I hold a paper back book and bend it, I do not understand this idea of bending space. If I suppose the book and the air around it are really space, when I bend the book, that part of "space" goes into other parts of "space". Further, there must be space where the bending space once ways. What...

So, I've been doing a lot of spot welding and research/development of this manufacturing process I came up with a while ago, both of which involve high-energy capacitor discharges, and my previous 2.3kJ capacitor bank just wasn't cutting it anymore. So, I invested in 100 "Green-Cap" 2.7v 100F...

I'm wondering how the inventor of bicycle knew the fact that it would be possible to maintain balance on two wheels. Most kids fall off and bruise themselves in the beginning and there's no way of learning a bicycle other than trial and error. How did the inventor figure this out?

Hello everyone :) I came across a strange situation today when I was listening to my music with my headphones on. When I pressed play to a song, the instrumental intro started off fairly normally (although the audio sounded a little "thinner" than usual, as if compressed), and then, when...

Dear PF Forum, I realize that there are 4 basic forces in our universe. Two of them are gravity and electromagnetic force. Electromagnetic travels at the speed of light. And it seems that Gravity travels/propagates at the speed of light also. Light is bent by gravity. What about gravity? Is...

Dear PF forum, Do anyone know, why music interval is always \sqrt[12]{2}?

So this sounds homework question but I promise its not. At least its not mine. I saw it on a website because someone made it funny because of what they answered (drew an elephant if you know the one I'm talking about) Anyway, so the problem was a block of mass m = 5 kg falls starting at rest at...

I'm not sure where to post this, but I wanted to show this just because of the incredible nature of the phenomenon. It's just the dust from a slow running wet grindstone. I assume just vibration, but the more carefully you look the more unbelievable it becomes. As the grindstone ran, some of...

Homework Statement http://lon-capa.bd.psu.edu/res/psuerie/gwb6/physics/optics/e1p4.png A thin 200nm film of oil (n = 2.0) floats on water (n = 1.33). To a normal human, what wavelength will the film appear when viewed from above (nearly perpendicular to the film)? Homework Equations for...

Homework Statement (a) Draw the feynman diagram for ##p \bar p \rightarrow## reaction. (b) Find an expression for mass of the particle. (c) Find an expression for number of ##\mu^{+} \mu^{-}## produced. (d) Find an expression of ##n_{jj}## in terms of ##m_{inv}## and its spin. (e) Deduce the...

Homework Statement I found out this reaction series in my textbook which is as: ##2Cu(NO_3)_2+2Na_2S_2O_3 \longrightarrow Cu_2(NO_3)_2 +Na_2S_4O_6+2NaNO_3## ## Cu_2(NO_3)_2+Na_2S_2O_3 (excess) \longrightarrow Na_4[Cu_6(S_2O_3)_5] ## Though it is not balanced(latter one) but my question is about...

I'm a programmer/electronics student and I recently bought a GPS which I hooked up serially with my laptop. I didn't get into much detail of encoding the string which is output from the TX/RX pins of the GPS so I downloaded, a ready made program called "ublox 6". Longitude and latitude are...

Homework Statement There are two forces on the 2.43 kg box in the overhead view of the figure but only one is shown. For F1 = 20.0 N, a = 11.4 m/s2, and θ = 33.0°, find the second force (a) in unit-vector notation and as (b) a magnitude and (c) a direction. (State the direction as a negative...

from a malayalam language newspaper i read about Higgsboson that is according to standard model the Higgsboson is the piece of the atom that endows all the other piece with their mass. when electrons,quarks,etc are associated with higgs field they get mass. the light particle called photons have...

http://www.telegraph.co.uk/culture/star-wars/11547237/Young-Yoda-turns-up-in-medieval-manuscript.html']http://i.telegraph.co.uk/multimedia/archive/03272/yoda2_3272229a.jpg http://www.telegraph.co.uk/culture/star-wars/11547237/Young-Yoda-turns-up-in-medieval-manuscript.html

Hello everyone, I recently encountered that dreaded moment when walking where you get a face full of an seemingly invisible spider web. It got me thinking about why these webs are so difficult for humans to distinguish; unless of course we see them at the correct angle. Do they somehow bend...

Hi Likely a stupid question. If atoms vibrate with heat, why don't hot objects make a sound, i.e transferring vibrations to the surround atoms (air) into our eardrums? They vibrate on ultra-infra sound? Or it's a extremely weak sound? or this is not the same vibration as the cause for sound? or...