Surface Definition and 1000 Threads

Sorry i don't understand English very well , if someone want to explain to me this problem?

I start by parametarize the surface with two variables: $$r(u,v) = (u, v, \frac {d -au -bv} c)$$ The I can get the normal vector by $$dr/du \times dr/dv$$ What limits should I use to integrate this only within the elipse? I could redo the whole thing and try write r(u, v) as u being the...

My query in only on the highlighted part...c.ii. Find the question below; Find the markscheme here part c(ii) does not seem correct as i have; ##A_1=0.5 ×(0.65+0.84)0.3 ×2=0.447m^2## ##A_2 = 0.65 ×1.6=1.04m^2## ##A_3 = (0.3146 × 1.6)2=1.00672m^2## Total surface area =...

Greetings All, I have confusion to establish the orientation of a surface so please bear with me σ Those two surfaces are of course intersecting in z=10 on a circle . if I take the surface σ and I want it to be oriented so that it forms an acute angle with the axe Z , the orientation of the...

Hello, I've worked through the free-body diagram to compute the answer: tan(𝜃) = 0.67 𝜃 = arctan(0.67) = 33.822... The answer is supposed to be approximately 42. Yet, tan(42) is not 0.67, is the suggested answer wrong?

Summary:: Surface tension experiment Does anyone have an idea about a SURFACE TENSION experiment to present as university class work? An experiment that is not too "simple" and repetitive (like things floating under water), and that is well designed.

I don't get what is meant with the last part: that takes any one given point to any other given point. Thanks in advance

Greetings All! I have hard time to make the difference between the equation of a closed solid and a cartesian surface. For example in the exercice n of the exam I thought that the equation was describing a closed solid " a paraboloid locked by an inclined plane (so I thought I could use...

I have no idea where to even start with this, please help. I barely even know what integral of motion means.

From what I think, to find the bound charges of a block on the top and bottom surface I have to find the electric field or the displacement (D). However, I'm not sure how to proceed with a cube. For example, with a sphere ##E = \frac{Q}{4\pi \epsilon_0 r^2}## since r is constant. For a cube, it...

This problem is Wald Ch. 10 Pr. 2.; it asks us to show that ##D_a E^a = 4\pi \rho## and ##D_a B^a = 0## on a spacelike Cauchy surface ##\Sigma## (with normal vector ##n^a##) of a globally hyperbolic spacetime ##(M, g_{ab})##. Using the expression ##E_a = F_{ab} n^b## for the electric field gives...

Let ##\mathscr{H}## be a constant-##v## cross-section of the event horizon (area ##A##). The expansion is the fractional rate of change of the surface element, ##\theta = \frac{1}{\delta S} \frac{d(\delta S)}{dv}##. The problem asks to prove the formula ##\frac{dA}{dv} = \frac{8\pi}{\kappa}...

Trying first with lagrange multiplier ##grad(f) = (2x + y, 2y + x)## ##g = x^4 + y^4 -8 = 0## ##grad(g) = (4x^3, 4y^3)## $$grad(f) = \lambda grad(g)$$ gives us 2 equations (1) ##2x + y = \lambda4x^3## (2) ##2y + x = \lambda4y^3## From (1) we get ##y = \lambda4x^3 - 2x## insert that into (2) and...

Hello guys, I am getting more and more confused each time I try to get a definitive answer on this doubt: what's the acceleration at the contact point between a surface and a wheel spinning on it(without slipping). Considering this standard FBD for the above-described situation, (the direction...

I've double-checked my equations and can't find what's wrong. First I calculate the partials: $$f_x = (2x - 2x^3 -4xy^2)e^{-x^2, -y^2}$$ $$f_y = (-2yx^2 + 4y - 4y^3)e^{-x^2, -y^2}$$ By setting f_x = 0 I get: $$x^2 = 1 - 2y^2$$ Then I calculate f_y = 0 $$-2yx^2 + 4y - 4y^3 = 0$$ I plug in the...

I calculate f_x to be $$f_x = (2x - x^2)e^{-x-y}$$ $$f_y = (1 - y)e^{-x-y}$$ f_x = 0 when x_1 = 0, x_2 = 2 f_y = 0 when y = 1 This gives two critical points: (0, 1) and (2, 1) which yields e^-1 and 5e^-3 respectively. I then check the x line and y lines by doing $$f(x, 0) = x^2e^{-x-y}$$ $$f_x...

if a metric like ##ds^2=dr^2+r^2d\theta^2+r^2\sin^2\theta d\phi^2 ## is given, we know it corresponds to a sphere in spherical coordinates . if you are given an arbitrary metric with two variables for example ##ds^2=\frac{du^2}{u}+dv^2## is ther guarenteed to be a surface embedded in ##R^3##...

According to Cauchy's stress theorem, the stress vector ##\mathbf{T}^{(\mathbf{n})}## at any point P in a continuum medium associated with a plane with normal unit vector n can be expressed as a function of the stress vectors on the planes perpendicular to the coordinate axes, i.e., in terms of...

Summary:: Does the surface area of a parachute affect its drag coefficient? If so, how? I have been trying to figure out the effect of surface area on the drag coefficient of a parachute. I have designed a lab in which parachutes of different surface areas are dropped and the terminal velocity...

The classical free surface profile for the solitary wave for irrotational and incompressible fluids for small amplitude and long wavelength is the classical Korteweg-deVries(KdV) equation given by:\frac{\partial\eta}{\partial t}+\frac{\partial \eta}{\partial x}+\eta\frac{\partial\eta}{\partial...

Hello, I'm reading FLP vol II, and I would appreciate some help to understand the argument supporting Figure 6-6. Basically they claim if a sphere has non-uniform charge distribution whose surface density is proportional to the cosine of polar angle, then this surface charge distribution is...

a. I solved a but I don't fully understand how it works. $$z = f_x'(1, -1)(x -1) + f_y'(1, -1)(y+1) = 2(x-1) + 3(y+1)$$ Eitherway it's b that's my issue. I can find the gradient of both plane and surface, but trying to do "dot-product of both normals = 1" will give an equation involving two...

hi guys I came across that theorem that could be used to check if a surface represented by the function f(x,y,z) = λ could represent an equipotential surface or not, and it states that if this condition holds: $$\frac{\nabla^{2}\;f}{|\vec{\nabla\;f}|^{2}} = \phi(\lambda)$$ then f(x,y,z) could...

Hi, So my goal is to compute the integral of the "curl" of the vector field ##A_i(x_i)## over a 2-dimensional surface. Following a physics book that I am reading, I introduce the antisymmetric 2-nd rank tensor ##\Omega_{ij}##, defined as: $$\Omega_{ij} = \frac {\partial A_i}{\partial x_j} -...

When small object such as needle is put on the surface of water it displaces small amount of water which creates a depression under the object. Such depression increases surface area of the water because of which surface tension tends to decrease it. Explanation why surface tension balances the...

This method calculates surface tension based on force balance acting on the ring placed on the liquid surface: $$ F = G + \gamma L $$ where ##G## is weight of the ring, ##L## is wetted length of the ring which is equal to its circumference, ##F## is outer force of tensiometer acting on the ring...

Owens - Wendt model is used for calculating surface energy on liquid - solid interface and it is given by following equation: $$ \gamma_{sl} = \gamma_s + \gamma_l -2(\sqrt {\gamma_l^d \gamma_s^d} + \sqrt {\gamma_l^p \gamma_s^p}) $$ So, if we use liquid and solid of known surface energy as well...

What is the delta-v requirements from each of the Earth-Moon lagrange points to landing on the lunar surface? What would be the best software I could use to visualise and calculate that kind of thing? Thanks.

This doubt is confusing to me. I know it's something to do with conductors and insulators, but cannot explain. Conductors have mobile/free electrons unlike insulators. Having free electrons doesn't seem to explain this difference of charge distributions.

Found this map website. Click on the map somewhere, and it will figure out the path surface water, from that point, would take, as it flows to the sea (or where-ever). It also makes a 3D fly over if you click the path. It doesn't show drainage basins, which would have been nice, but there...

General relativity tells us that an object in free-fall is actually inertial, following a geodesic through curved spacetime, and not accelerating. Instead, it's objects like us, on the surface of a large body, that are accelerating upwards. Maxwell's equations also tell us that accelerated...

A hypersurface being spacelike (a local condition - every tangent to the surface being spacelike) does not preclude that points on it cannot be causally connected (one is in the future or past light cone of the other). A classic example is a spacelike spiral surface. Typically, for foliating a...

I've read a lot about Gato / Balao / Tensch class submarines, the ones America used in WWII, and I can't seem to sort out the specific consequences of a dead battery. A lot of you are diesel experts, so maybe someone here knows? Historical accounts are vague. Dead batteries are certainly a big...

When I look at the relevant equations, then there is no mention of field for a point on the surface of the shell, so it gets confusing. On the other hand, I feel the radial E will get stronger as we approach the surface of shell and magnitude of E will approach infinity.

Hi Guys - I have very simple question but I cannot get my head around. Say if we cut pipeline into one section (12m) then close each cut end with temporary plugs Water depth is 100m. Before the cut there is seawater inside the pipeline. Now I understand there is no differentiated pressure...

how to find volume and surface area of this without using the upper lid

Equation of circle: ##x ^2+y ^2=1##. Is this equation describing boundary or a surface? Thanks.

I think most refrigerators have their cases and doors attracting to magnet, but their surface look like plastic plate. what are they actually made of?

So, at home I have a weatherstation which measures solar irradiation in the east, south and west in lux. I can read in these measured sensordata. From these measurements, I would like to calculate the solar irradiance on my windows. The solar energy formulas could help me with that. The work of...

Hi, From suppliers of bearings, some of them specify the maximum bearing (surface) pressure or the maximum load rating (static or dynamic). What's the difference between this two? And which is most commonly used during selecting and calculating bearings in a mechanical design? Thanks in advance,

When I plug in the numbers I get ##2.9513\cdot 10^{-5}C/m^2##, not ##17.6\cdot 10^{-6} C/m^2##. Can someone point out where I'm going wrong?

Hey! :giggle: We have the function $$f(x,y)=(x-3)^2+y^2+(x-y)^2$$ and I have shown that at $(2,1)$ we have a minimum and so $f(2,1)\leq f(x,y)$ for all $(x,y\in \mathbb{R}^2$. I did that in this way: I calculated the gradient and set this equal to zero and found that the only critical point...

I did a little experiment recently where I took a plane mirror and held it underneath a ceiling light. Then, I began to lower my head so that my view was closer and closer to the surface. When I did this, the image of the light began to drift lower and lower in the mirror until it completely...

The method to solving this is to equate forces along a portion of the balloon through which ##\sigma_L## acts, and another portion through which ##\sigma_t## acts. The former potion should be a circular cross section of the cylinder, while the latter will be a rectangular cross section. You will...

Summary:: Hi, I realized that surface tension is not covered in introductory physics textbooks. Where can I get a good introduction on surface tension? *info provided should be about the same depth as topics in Halliday, Young. Hi, I realized that surface tension is not covered in...

Does anyone have some bibliography about necks in FCC structure Fermi surface? I have to solve this problem and I have no idea how to start. Thanks.

I'm re-watching Star Trek TNG and I just started the episode where they encounter Scotty aboard a ship that's crashed into a Dyson sphere. That got me thinking. What would the mass and external surface gravity of a Dyson Sphere be? I've done the math myself, but I'd appreciate someone double...

Hello everyone, I am trying to do some calculations for the energy output of a solar farm that I am designing as my dissertation. However, when I trie to calculate the following formula: Wp = ηpvGBA from Equation (11) above, where: ηpv is module efficiency (18.4%) GB is solar irradiance (3.8)...