Surface Definition and 1000 Threads

Stephen hawking came to know of a study that stated that surface area of an event horizon increases. So he said that since area has increased Entropy also had increased. But why does surface area of an Event Horizon increase?

A block is at rest at the top of a frictionless hemisphere of radius r. It is slightly disturbed at starts sliding down. I already know where it will leave the surface (height = 2r/3). My question is, WHEN will it leave the surface?

Homework Statement http://ocw.mit.edu/courses/mechanical-engineering/2-06-fluid-dynamics-spring-2013/assignments/MIT2_06S13_ps2.pdf Problem 7[/B]Homework Equations ##F=2*V/(a^2)*\sigma*cos(180-\theta)## The Attempt at a Solution With the problem statement given, it seems like the component of...

Homework Statement A uniform rod of mass M and length L can rotate around point P which is at position x from one end of the rod as shown in the figure. The rod is gently placed on a rough horizontal surface that has a friction coefficient μ. and at t=0 starts rotating with angular velocity...

The event horizon is a null surface in spacetime separating events that are causally connected to an observer from those that are not. Does anyone have a good, simple argument on why it must be a null surface?

Im having trouble convincing myself that a charge located anywhere inside a conducting sphere will create an induced charge on the surface of the sphere with an electric field that is completely uniform. This doesn't make much sense to me. Also same with how the electric field inside solid...

Homework Statement The problem and its solution are attached in TheProblemAndSolution.jpg. Homework Equations Stoke's theorem: ∮_C F ⋅ dr = ∮_C (F ⋅ T^) dS = ∫∫_S (curl F) ⋅ n^ dS The Attempt at a Solution In the solution attached in the TheProblemAndSolution.jpg file, I don't understand...

If I have a U-shape wire frame and it contains a straight sliding wire and I dip this in soap, a film forms between the sliding wire and the boundary of U shape frame. Why is the force due to surface tension F = 2Tl where l is length of sliding wire? They say there are 2 layers in contact...

Homework Statement What exactly does it mean for a surface to span a contour/curve? For example, which surface(s) span the contour/curve defined by the equations x^2 + y^2 = 1 and z = y^2? Homework Equations N/A The Attempt at a Solution I'm not sure if I'm saying something nonsensical, but...

I had this problem in my exam. It required me to calculate relative permittivity of a dielectric slab which acquires a surface charge density of 800micro Coulomb/m^2 when subjected to an electric field of 10^8 V/m. Applying E=sigma/(2epsilon), I got relative permittivity as 0.45 which is less...

Homework Statement A spherical air bubble in a lake expands as it rises slowly to the surface. At the point it starts to rise, the pressure is 2.00 atm, the temperature of the water is 10.0 ∘C, and the radius of the bubble is 5.00 × 10^−3 m. At the surface, the pressure is 1.00 atm and the...

Homework Statement ##\iint_S (x^2+y^2)dS##, ##S##is the surface with vector equation ##r(u, v)## = ##(2uv, u^2-v^2, u^2+v^2)##, ##u^2+v^2 \leq 1## Homework Equations Surface Integral. ##\iint_S f(x, y, z)dS = \iint f(r(u, v))\left | r_u \times r_v \right |dA##, The Attempt at a Solution...

Hi, I have a simple problem. A Lambertian emitter has the shape of a square planar surface, with area Ae=4mm2, total power P=1mW, and is located in yz plane. Another square planar surface, with area Ad=6mm2, is located in the xy plane, at a distance d=10cm to the Ae, and is tilted 20 Degrees...

If you increase the surface tension of a liquid, does it change the average bond strength of the liquid?

What's the difference between surface tension and capillary force? Surface tension, a tensor, is the force per unit length. Again surface energy is the energy required to increase the surface area by one unit. Is the surface tension a capillary force?

I am writing a simulation in MATLAB of particles that perfectly reflect off of a surface. However, my question is physics based, not code based. So here is my issue. A particle is traveling towards a flat plane in space at z=1 with a velocity vector of [0,0,1]. The normal vector of the...

If the magnetization vector is in the z direction, is the bound surface current of a cube always 0, since z cross z is 0, and x and -x cancels and y and -y cancels out?

Hi How is circular surface area values square rooted ??. I am using this formula r2Xπ=mm2 to calculate the surface area of a circle but i want to know if there is a formula to get back to the diameter or the radius of the circle ?. example i have a circular surface area of 5.26mm2 and i want...

Homework Statement Homework Equations ∫∫D F((r(u,v))⋅(ru x rv) dA The Attempt at a Solution [/B] I got stuck after finding the above, at where the double integrals are. :( May I know how do I find the limits of this? (I always have trouble finding the limits to sub into the integrals...

[FONT=Tahoma]I have been investigating the damping of an oscillating mass on a spring by a piece of card of varying surface area, in order to work out the damping constant λ for the equation y = A₀ e-λt sin(ωt). I took the natural log of the amplitude of each successive oscillation and plotting...

I have a problem with some question I had to answer for the Surface Brightness \Sigma \propto \frac{Flux}{Angular~area}= \frac{F}{\Omega}. I was able to show that \Sigma \propto (1+z)^{-4} Then the question asks whether knowing its value for known candles or yardsticks, is a good way to...

Homework Statement A) Suppose you are on Earth's equator and observe a satellite passing directly overhead and moving from west to east in the sky. Exactly 12.0 hours later, you again observe this satellite to be directly overhead. How far above the Earth's surface is the satellite's orbit...

Is the air pressure acting on the top of the head of a person standing in a room equal to the air pressure acting on a same area on the floor of the same room? Since F = pA , it seems as if the air pressure is independent of the height of the surface on which it is acting. But that doesn't seem...

Homework Statement A block of mass m=2kg and one of mass M=8kg have initial velocity zero. The friction coeffecient between m and M blocks is 0.3 Between block M and the surfasse there is no friction. L=3 metres F is a force constant and horizontal with magnitude 10 N, applied on block m and so...

Hi, I'm trying to solve this problem and I'm stuck. What I want to do is determine the kind of surface from this equation: x2-2y2-3z2-4xy-2xz-6yz = 11 Matrix representation: 1 -2 -1 -2 -2 -3 -1 -3 -3 I want to find the eigenvalues so I write the characteristic equation like...

After watching these videos about Computational photography: and lensless image sensors: was wondering if it is at least theoretically possible to calculate the light of the surroundings of a white surface just from the light information on that surface. For instance taking a picture of a...

Homework Statement The problem is given in the attached file. Homework Equations Divergence theorem, flux / surface integral The Attempt at a Solution [/B] As you can see I got the question correct using Divergence theorem. But I wanted to make sure that I could arrive at the same answer...

why surface area increases with foldings ,invaginations,roughness and powdered form?please someone explain concept of surface area. what is difference between perimeter or (circumference in case of circle)and surface area? Mentor Note: Two posts have been merged.

Homework Statement Evaluate ∫∫ F⋅dS, where F = yi+x2j+z2k and S is the portion of the plane 3x+2y+z = 6 in the first octant. The orientation of S is given by the upward normal vector. Homework Equations ∫∫S F⋅dS = ∫∫D F(r(u,v))⋅||ru x rv|| dA, dA=dudv The Attempt at a Solution [/B] Since...

Homework Statement With what initial speed must an object be projected vertically upward from the surface of Earshot rise to a maximum height equal to Earth's radius? (neglect air resistance.) Apply energy conservation. Homework Equations ##E_{k_1}+E_{g_1}=E_{k_2}+E_{g_2}##, however since...

I'm having trouble evaluating this surface integral. This would be very simple to solve if the parameter domain of the variables u and u was a square region. However, that isn't the case here. I've tried using a change of variables and saying that u = r cos x, and v = r sin x. Where 0 < x < 2pi...

1. Calculate the force needed to move the wire in the figure (Figure 1) if it holds a soapy solution (surface tension is 0.025 N/m) and the wire is 16.0 cm long. Express your answer to two significant figures and include the appropriate units. 2. γ(surface tension) = F (force) / l (length)...

Homework Statement Picture:[/B] The Attempt at a Solution [/B] Can someone please help..There's no answers and I think my answer is very wrong, as you can see I have pretty much no idea what I'm doing. Thanks Edit: Where it says net force I meant to say net force per unit width. Edit2...

Would Electric Field on the surface of a conductor point inwardly due to the excess of negative charges on the surface? Lastly, I cannot seem to conceptualize why the E field inside the conductor is zero? Is it due to the protons that are in opposition to the electron's efields? Thanks...

Homework Statement The object has a mass of 10 Kg. And it has a contact surface of 25 cm^2. How much pressure do the object apply to surface? Give your answer is Pascals. Homework Equations N The Attempt at a Solution [/B] So, I think I need to divide the mass with with the surface area to...

Homework Statement Find the area of that part of the cylinder x^2 + y^2 = 2ay that lies inside the sphere x^2 + y^2 + z^2 = 4a^2. Homework Equations [/B] If a surface S can be parametrized in terms of two variables u and v, then dS = Norm[dR(u,v)/du x dR(u,v)/dv]. The surface area is given...

This problem is actually an example I'm working through... 1. Homework Statement We are trying to estimate the (magnitude of the) electric field in the light waves from the sun hitting the surface of the Earth. Homework Equations The Poynting vector for a sinusoidal EM wave has magnitude...

Homework Statement The value of acceleration due to gravity at a point P inside the Earth and at another point Q outside the Earth is g/2 (g being acceleration due to gravity at the surface of earth). Maximum possible distance in terms of radius of Earth R between P and Q is Ans: R/2 (...

The diagram shows how a force along the x-axis varies with location. A block of mass 7.20 kg moves along the x-axis on a horizontal frictionless surface, influenced by this force. (Graph is attached) A) How much work is done by the force as the block moves from the origin to 8.0 m? B) If the...

The school in which I teach is going to pilot a tablet for each student in a class next year. My physics class is going to be part of this pilot. Currently they are looking at ipad/surface/chromebook. Does anyone have input good or bad on any of these for use in class as well as with labs...

Hey everyone, I was recently reading a paper on surface enhanced Raman scattering, and it mentioned that plasmons (and for that matter surface plasmon polaritons-where my interest lies) are sensitive to the surface to volume ratio of the structure. I can begin to understand intuitively with...

Work done = force applied * displacement So if I exert N1 force on a mass placed over a friction less floor, then the displacement = ∞. Then won't the work done = ∞. How is possible?

Homework Statement Calculate the gravitational force acting on a 9.6-kg mass...? 1.5 x 10^4 m above Earth's center. How do i solve this?? Homework EquationsThe Attempt at a Solution the answer is 17N but i don't understand how

If an object falls through a planet's entire grav. field, before impact it's velocity will be the escape velocity. I assume the time dilation for an observer on the object will be the same as for an observer on the planet. They're not added together. Another point - since time dilation on a...

Homework Statement A thin spherical shell of radius R carries a surface charge density of the form kcos 3 θ . Find the electric field inside and outside the sphere and demonstrate explicitly that its components satisfy the relevant boundary conditions at the surface Homework Equations The...

Homework Statement There is an infinite conducting cylinder positioned at the axis with radius R. An infinite line charge (+λ) is placed distance d from the axis and d>R. I was supposed to 1. Find the potential and then 2. find the surface charge on the cylinder. Homework Equations V = -∫...

A couple friends and I were brainstorming an idea today and thought of a way to make a pump using the waves in the ocean for enrgy. So what it comes down to is say a 6cm i diameter steel ball in a tube, each side of the tube could have "pillows" that are part of a "membrane-pump". When the...

I have went through the thread and looked at the explanations for surface tension, and I have also went online to about 10 different websites, but I have not yet been able to figure out this concept. I think it is just my inability to understand and I need perhaps a different way of explaining...

Can someone please look at the diagram below and tell me how u1 is obtained. If it is through the use of m3 please explain how the gradient m3 is obtained.

Homework Statement A thin spherical shell of radius R carries a surface charge density of the form kcos3 \theta Find the electric field inside and outside the sphere and demonstrate explicitly that its components satisfy the relevant boundary conditions at the surface. Homework Equations...