Body Definition and 1000 Threads

Homework Statement 2. Consider a metal sphere of radius R and heat capacity C, initially at a temperature To which is much hotter than the background temperature. a) Derive an analytical result for the temperature of such a sphere as a function of time. Clearly state any simplifying...

Homework Statement The mass of an electron is 9*10^-31kg. Find the charge in mass of a charged body if it loses 1 Coulomb of negative charge. Use your answer to explain why electricity was originally thought to be weight less. 1 coulomb = 6.642*10^18 elementary charges. Homework Equations...

Per Wikipedia (Outer Space) referencing Davies, P. C. W. (1977), "...the mean free path of a photon in intergalactic space is about 10E23 km, or 10 billion light years." Per Lawrence Krauss (1999), it is longer than the size of the visible universe. What is the current thinking about this?

Hello Everyone, Sunlight is composed of UV, visible and infrared (IR) over a wavelength range from ~290nm to ~2500nm. When we are exposed to sunlight and feel hot, is it because of the absorption of energy at the visible wavelengths and FIR, i.e . infrared wavelength much larger than 2500nm? I...

I explain it better. If we bring an electron from higher to lower energy level, the energy gap will be emitted as electromagnetic wave, because of the conservation of energy. When the same situation applies for a physical body, for example letting if falling down from some height, what does it...

Hello, If two bodies, who say start with ##T_{cold}=T_c## and ##T_{hot}=T_h## and then they are brought in contact with one another and then after some time they both have the same temperature. What would be the entropy of the entire system? Also another quick question, I've looked at some...

No I'm not a particularly big person with a weight issue. Somebody asked me this question and I don't know the answer, but somebody here will. OK, it's now accepted that dark matter is everywhere in the Universe, it tends to clump with regular matter because all matter is subject to gravity...

Hi! I'm trying to understand a perfectly black body. So the definition I have found is that a black body is one that absorbs radiation of ALL wavelengths and reflects NONE. Therefore it appears black at low temperatures. And when heated it emits radiation of all wavelengths making it appear...

Hello everyone. This is my first time on the physics forum, but I think I'm going to be a regular here. I was reading a paper that outlined various ways to approach solving dynamic problems. The first approach outlined by the author is D'Alembert's principle of virtual work. In describing...

Hello,Ive got a question and wondering if there is someone that could help me? I would really appreciate it! I am studying for an exam that I am going to have in a couple of weeks and it has been going great besides that I have been stuck on a question about tension in a preloaded system with a...

I am trying to find out the amount of force that a free-falling body will have, as it hits the ground from a distance of 2000 km from Earth's surface.(Considering air resistance) What I know about the body: Area of the body=20199.04 mtr² Density of body=985 Kg/m³ Thickness of body= 75 mtr...

Homework Statement Homework EquationsThe Attempt at a Solution why are my reactions at A considered wrong? I know that AC and DC are two force-members

Homework Statement Homework Equations Trying to find the reaction forces at E. But, I am kinda confused about drawing the free body diagram for each member. I know that member AD and CB are two force members. What is wrong with my free body diagram then? The Attempt at a Solution i...

Homework Statement Homework Equations The Attempt at a Solution Is the particle moving under the influence of a single central force ? Since the force always acts towards the center , work done by the force is zero . Energy is conserved . Potential energy at a particular radius can be...

Homework Statement Charged sphere with a mass of 15 mg and charge 2 nC moves with a speed of 15 cm/s towards a fixed point charge of 3 nC. How close will sphere approach charge? Homework Equations K=(1/2)*mv2 U=k*(Q1Q2/r) The Attempt at a Solution So I am not sure I approached correctly but...

Homework Statement A hemispherical portion of radius R is removed from the bottom of a cylinder of radius R. The volume of the remaining cylinder is V and its mass is M. It is suspended by a string in a liquid of density ρ where it stays vertical. The upper surface of the cylinder is at a depth...

The field of quantum mechanics was launched with scientists struggling to understand blackbody radiation. My question is: what is the source of this observed radiation? Is it the nuclei in the matrix of the metal jiggling around ever more energetically as you heat up the metal? Or is it the...

Can black body retain it`s absorbed heat energy? If yes, then why we can not convert this energy into a usefull form such as into electric energy as solar do?

Homework Statement A body of mass m, moves with a velocity v, and has a certain kinetic energy. What velocity would a body of twice the mass have to move to have the same kinetic energy. Homework Equations K.E=1/2mv2 The Attempt at a Solution I made an equation 2m1/2*v12/2= m2v22/2 from here...

Homework Statement :[/B] Ok, so my exams are coming and all sorts of crazy thoughts are banging my mind and now I have a question regarding a very simple law of physics, the funniest part, this is my last month of high school life...so at this juncture of life, i am having this crazy question...

Homework Statement Everything we know is in the picture. There is no friction between the body and the wagon and between the wagon and the floor. What will be the maximum height that the body will reach on the wagon? (Answer:0.008v02) What will be the velocities of the body and the wagon once...

I'm just trying to develop a general understanding of the 'twin paradox', so my description of this is will be a bit poor. I feel like I have a sound understanding so far on the topic, but the only thing that I can't seem to find an answer for is this scenario; Say you have the classic twin...

I was working at the observatory and uh someone came in with a question about landing in Jupiter- right away my brain was like no, it’s a gas giant and there’s too much pressure for a probe to make it to the solid surface, but I’ve also been trying to think of it in terms of the force applied by...

Hi I would like to know if there is any physical or medical scientific tests I can take to know/confirm my energy levels/body energy levels and will level when it comes to motivation. the reason for wanting to take these tests is that I have a severe mental brain neurological disability known...

I am solving the Laplace equation in 3D: \nabla^{2}V=0 I am considering azumuthal symmetry, so using the usual co-ordinates V=V(r,\theta). Now suppose I have two boundary conditions for [V, which are: V(R(t)+\varepsilon f(t,\theta),\theta)=1,\quad V\rightarrow 0\quad\textrm{as}\quad...

Hello Everyone.. Consider a small moving mass following a spiral path away from center and the body is rotating about its center as well. At some time the body impacts with a relatively bigger mass and transfers some of its energy to it. If we want to make an equivalent system with only linear...

Hi folks, This week I have a question about rigid body dynamics analyses in CAE. This is in relation to the final year project of my degree. Over the past few months I've been working with AnSys 18.1 for FEA however, I've reserved AnSys exclusively for static analyses. For rigid body dynamics...

Homework Statement In the figure there are a block 1 of mass ##M##, a pulley (disk) of mass ##M## and radius ##R## and a second block of mass ##2M## on an inclined plane with an angle ##\alpha## with respect to the horizontal. On this plane the static friction is ##\mu##. The wire does NOT slip...

Hi, I would like to ask you what happens when you change (gradually) a mass of one body in a classical two-body-problem. May it lead to such results? Many thanks. Flor

Hello Forum, A quick discussion about blackbody theory. As a premise, this is what I know: A blackbody is an ideal body that absorbs all types of radiation incident on it, no matter its wavelength. Once absorbed, the energy is used to increase the blackbody's temperature and when the...

Here I have drawn the free-body diagram for a rock (but could really be any object) which is being pulled upwards. Fa represents the applied force (let's say...by a rope) Fg represents gravity/weight of the object Ff represents friciton, i.e. the small amount of air resistance But here's my...

Homework Statement Homework EquationsThe Attempt at a SolutionThe energy density is given as ## u = \frac { 8 \pi {\nu }^2}{c^3}~ \frac { h \nu} {e^{ \frac { h\nu}{k_B T}} – 1}.## EDIT : I put the constant C. ## \frac { u( 2 \nu) } {u(\nu)} = C \frac { {e^{ \frac { h\nu}{k_B T}} – 1}...

Imagine a long brick in outer space. You apply a force tangential to the center of mass. The brick accelerates in a transitional and angular fashion. There are no constraints or fixed axis. How would I calculate the translational and angular acceleration? I would like to run some simulations...

I have been trying to understand the role of a cavity as a black body radiator in the derivation of planks black body radiation law but it has left me with 5 main questions: 1. If an object is a perfect absorber it must also be a perfect emitter, meaning that (allowing for a cavity not being a...

Hi, I finished my first Bachelor in Physics, than continued my studies by finishing second bachelor in mechanical engineering. I am a very enthusiastic pilot, maybe that's the reason why I'm pulled towards fluid dynamics and soft body dynamics. Well my dilemma is the following: I don't know...

Say I wanted to set up EFE for the Earth and moon. How do I actually go about filling the stress energy tensor? I'm referencing the wikipedia page. So the time-time should be approximately E/c^2V, so for the Earth moon system ##T_{00} = \frac{3}{4\pi r_E^3}\frac{1}{c^2}(M_Ec^2 + 2/5...

Homework Statement this has been bugging me for a while now the angular momentum about any point p is given as ## \vec {L_p} = \vec {R_{cm,p}} \times \vec {P_{cm}} + L_{cm}\\ ## now if the body precessing around z axis and spinning about its own axis then angular velocity of body in lab...

[Moderator's Note: Thread title changed to better reflect the problem statement] Homework Statement A body of mass m is on a disk of mass M=2m and radius R, initially static and free to spin around its center. The mass mm goes around a trajectory described in the image below with constant...

Hello! I am implementing the three body restricted problem numerically (2 of them are massive and the 3rd one is not affecting them, so it is just moving in the potential created by them). I implemented it and if I put the 3rd one close to one of the big ones it moves in circles around it, while...

Homework Statement A body that is on a horizontal surface begins to move under the action of horizontal force equal to 60% of its weight. Force acts for a while, then stops acting. Determine the total time of movement if the body has traveled a distance of 24m. Homework Equations [/B] I'm...

During these days, I have asked my mother: What is better/worse for the human body: salt or sugar? Both of these substances are quite dangerous in high amounts, but which one is worse? Salt was used in food preservation, with its abilities (Which abilities? I have never understood this...) and...

Homework Statement On the axis of an infinite wedge that moves with velocity ##\vec{V}##, the body decays with the formation of a lot of splinters that fly away uniformly in all directions with velocity ##\vec{u}##. What should be the angle of the wedge that half of the splinters fall on its...

hi, i am studying about design the box carried on car. i am really stuck in how to draw free body diagram for when 3 or more boxes stack together on car running and braking. there are many example with 2 boxes but i don't know why i can't find any case with 3 or more boxes thanks in advance

Just to confirm a few points: A body frame rotates with a body. It need not be aligned to the rotation axis. Angular momentum vector always aligned with rotation axis (not deviates from it). An observer on the body surface (body frame) observes no motion on a body. Principal axis of rotation...

What does it mean where it says it provides couples on x-axis and z axis? Anyways what am I doing wrong? my procedure is finding tension in cables by summing moments about point A. then with the tensions, finding reactions at A. However when i sum the moments about A I get 3 equations 2...

I am currently performing failure analysis on an A356 Aluminum alloy wheel subjected to rotational loading, with a maximum load of 650 kgf and a torque of 4600 Nm. Cracks formed in the wheel after 1.3*10^6 rotations. My job is to perform a stress analysis to determine the regions of maximum...

Does body hair really grow back thicker each time you shave it? I hope this is just a myth. It's gotten me worried about shaving my facial hair too much.

I'll (hopefully) be starting a PhD program in hard condensed matter theory in fall 2018, and need to decide which courses to take this spring. I'm currently in the first semester of graduate quantum mechanics and would like to take the second semester (which covers relativistic qm, second...

In my Thermodynamics course, we recently learned about the saturation pressure and saturation temperature of different substances -mainly water. As you know, the saturation temperature at which a substance begins to boil is specific to a fixed saturation pressure. Water only boils at 100...

Hello everyone, I know that the any object, human body included, when the vertical line from its center of mass to the floor falls outside the base of support, topples under the influence of gravity: the force of gravity produces a nonzero torque that rotates the body. Is the human body able to...