# What is Surface: Definition and 1000 Discussions

A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is the portion with which other materials first interact. The surface of an object is more than "a mere geometric solid", but is "filled with, spread over by, or suffused with perceivable qualities such as color and warmth".The concept of surface has been abstracted and formalized in mathematics, specifically in geometry. Depending on the properties on which the emphasis is given, there are several non equivalent such formalizations, that are all called surface, sometimes with some qualifier, such as algebraic surface, smooth surface or fractal surface.
The concept of surface and its mathematical abstraction are both widely used in physics, engineering, computer graphics, and many other disciplines, primarily in representing the surfaces of physical objects. For example, in analyzing the aerodynamic properties of an airplane, the central consideration is the flow of air along its surface. The concept also raises certain philosophical questions—for example, how thick is the layer of atoms or molecules that can be considered part of the surface of an object (i.e., where does the "surface" end and the "interior" begin), and do objects really have a surface at all if, at the subatomic level, they never actually come in contact with other objects.

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1. ### Rate of EM emission based on surface characteristics

I would think the black painted surface is
2. ### Forces for bodies connected by a wire on inclined surface

Hello PhysicsForums! Here is my attempt at a solution for the problem stated above: Where m1 and m2 are the masses Where Ff1 and Ff2 are friction for each mass Where a1 and a2 is the resulting acceleration Where S is the fore of the wire (threadforce) Where FN is the normal force The answear...
3. ### Solve First Year Harmonic Motion Problem: Cylinder Rolling

Thank you guys for taking the time to read this - I'm decently struggling with first year and need some tips on how to properly conceptualize problems and learn what the right approach is on certain problems. Have a wonderful day, again thank you for checking this post out!
4. ### B Water surface under pressure

Hi togehter, this may be an easy one for most, but I'm really struggling with imagining the process. Suppose we have a compressed air vessel that is half filled with water. The pressure in the vessel drops from 10 bar to atmospheric pressure within a few seconds. How does the water surface...
5. ### Find tension in ropes connecting 3 masses being pulled on a surface

This is the problem and my answer below it. my friends said it's 250 N and I say it's 100 N based on what I solved what am I missing ?? my try:
6. ### Equipotential surface (test questions)

The answer to the first question should be a sphere since for very large distances the multiple charges will act as a point charge. 1(a) is correct answer. For the second question, I find it slightly vague. How can equipotential surface be zero, may be it's asking for the potential of...
7. ### I Surface area and length (percent increase relationship)

Hi all, While calculating the surface area for an object, I was told the below statement. However, I am not sure is this correct, please can someone help me to explain this with an example? Is the below statement always true? The surface area % increase should be in line or less than the %...
8. ### Pulling a yoyo over a surface with tension

My Work so far: So there is a Force F applied to the right and since we have a no slipping condition we have a static friction force fs to the left. So the only thing that can move the center of mass (cm) of the yoyo is rotation. F would lead to a ccw rotation and fs to a clockwise rotation...
9. ### what are the forces on a cell in a tree vs on the surface of a tree

Hey everyone. Let's say you have a tall tree. say, 10 m tall. Take a cubic cell 1mm in dimensions. Suppose the cell is at 1 m high in the center of the trunk of the tree. What are the forces acting on the cell? let's say tree cell's mass is t grams. its weight is F= ma = t (9.8) = 9.8 t...
10. ### MCNP6.2 - SDEF on a RCC surface

Hi everyone, I'm trying to set up a surface neutron source on the surface of a cylinder defined as a macrobody (RCC) and used also to define cell of the system. My aim is setting up a surface source where I'd like to give a specific spectrum (and DIR) at each surface defining the cylinder...
11. ### Electrons escaping a metal surface

In the low temperature limit ##\mu \approx E_F## and the Fermi-Dirac distribution is ##n(E) \approx g(E)/(e^{\beta(E-E_F)}+1)##. An escaping electron contributes ##\Delta j_z = -ev_z = -ep_z/m## to the current density. How can I calculate the rate that electrons escape at? I can't see how to...
12. ### Electron encountering metal surface (1D Step potential)

I am struggling with how to go about this; in particular, I'm not sure I understand what state is being alluded to when Ballentine says "For an electron that approaches the surface from the interior, with momentum ##\hbar k## in the positive ##x## direction, calculate the probability that it...
13. ### Downdraft table -blocking off part of table surface to increase flow?

Hello everyone. First post! I am struggling to understand an issue in our (histology) lab. We use large downdraft tables which extract the noxious substances we use, mainly formaldehyde, while we process surgical samples. These tables have a steel cover with lots of holes about 5mm diameter...
14. ### Surface density of the charges induced on the bases of the cylinder

The correct answer to this problem is: ##\sigma = \varepsilon_0E\frac{\varepsilon-1}{\varepsilon}## Here is my attempt to solve it, please tell me what is my mistake? ##E_{in} = E_{out} - E_{ind}## ##E_{ind} = E_{out} - E_{in}## ##E_{in} = \frac{E_{out}}{\varepsilon}## ##E_{ind} = E_{out} -...
15. ### Evaluate the outgoing radiation from an optical fiber on a surface

The geometric configuration that I am adopting is the following, I hope you understand. The optical fiber is positioned relative to the bottom surface at a height ##a## and an angle ##\alpha## with respect to the y-axis in the yz-plane with x = 0. ##b## is the distance between the origin and...
16. ### I Surface charge of neutral solids

Also referring to the post by @Kostik plus answers, I'm wondering about surface charges of neutral solids such as metals or carbon, for example. I only want to discuss large scale effects so that the solid can be treated as continuous. The atomic structure is averaged out. I also assume that...
17. ### Frequency selective surface radome

So I was reading about frequency selective surface radome, basically this is the kind of cover over the antenna which allow a certain frequency wave to pass through and reflect wave at any other frequencies. What I don't understand is the reflection vs transmission coefficient chart. So as I...
18. G

### Surface current on a spherical superconductor

I need help with part b. My solution: Have I done it right?
19. ### 3d plot of interference from 2 wave sources with 2d grid surface

Desired output similar to image, but without the objects and with better wave interference: I tried plugging the following into wolfram (I specifically want the values to be adjustable): plot z= H*e^(-m*sqrt((x-a)^2+(y-b)^2))*sin(k*(x-a)+k*(y-b) -w*t) +...
20. ### Measured Surface Resistivity Much Higher than Theoretical Value (Why?)

I recently conducted a physics lab to measure the surface resistivity of a conductive sheet of a paper with a carbon filler. The theoretical Rs is approx. 5,000 Ω/☐ for this paper and yet we have calculated two Rs values: Rs when Varying Length and holding Width = 10100 +/- 83.07 Ω/☐ Rs when...
21. ### MCNP Surface Tallies: F1 & F2 on Infinite Cylinders & Planes

Hi, I have a question concerning surface tallies like F1 and F2. You have to provide a surface for them. Since, surfaces are defined as infinite (infinitely long cylinders, infinitely extended planes) how can you write the surface tally of a cell? What are the actual tally surfaces for F1 anf...
22. ### Finding Charge Density on the Surface of a Slab

Here's my attempt at a solution, but when I plug it in, it gives me a power ten error. I don't really understand what I'm doing wrong here. I think all my variables are in the correct units and it asks for my answer to be in μC/m2. Any help is much appreciated.
23. ### Need a surface mount seal for chemical cabinet door

I want to build a mini chemical cabinet to try to eliminate odors in my garage as my wife thinks the car interior now smells. The chemical resistant rubber strip sealant is crazy expensive, but as the intended use will just be fumes with no actual chemical or fuel contact to the seals, can I use...

25. ### How does soap water membrane thickness affect surface tension?

1.If the thickness of soap water surface decrease, whereas the concentration remain the same, how will the surface tension change? 2. If the membrane of soap water start to evaporate, its thickness become thinner and it’s concentration increase, How will the surface tension change? Thank you!
26. ### Chemistry How to compute specific surface energy for cubes of varying sizes?

I got these values but I wanted to make sure I was doing it the correct way a) 0.548 J/g for system of 1 µm cubes b) 9.131 x 10^19 J/g for system of 1 nm cubes c) 273.890 J/g for system of 1 nm radius spheres
27. ### Electric field at surface of lead-208 nucleus

For this problem, The solution is, However why is ## r = (208)^{1/3}(1.20 \times 10^{-15} m)## Many thanks!
28. ### I Surface Absorptance Without Radiant Emittance

how can I go about finding the surface absorptance of a material if I'm not given the radiant emittance of the non- black body?
29. ### Find the surface area of the given solid

My question is on how did they determine the limits of integration i.e ##2## and ##3## as highlighted? Thanks
30. ### Force to smooth a 1 mm surface bump out of a steel of sheet

Roughly, how much force does it take to make 1 mm surface bump of diameter 16 mm circle area out of 1 mm thick steel plate of far larger area (e.g. a muscled hand pounding it laid over the base with 16 mm dia. hole by M16 bolt medium is viable enough) ?
31. ### B Oriented Surfaces & Surface Area: Investigating the Impact

I usually think of a sphere as the set of all points ##P_x##, that have the identical distance r to some point ##C## which is the center of the sphere. I calculate the surface area ##A## of the sphere as $$A=4 \pi (C P_x)^2$$ However, what happens if I think of the distance between the points C...
32. ### Average force when a bouncy ball collides with surface

What have mistakes/wrong assumption have I made in solving this question? I tried to solve the problem this way N.B. I assume that the j hat direction is up.
33. ### Doubt about solution -- Two masses connected by a rod moving on a surface

The doubt is about this question. Which the answer is They say that all the forces are pulling forces? How is this the case? How would this setup even work? I don't think block 2 could pull the rod.
34. ### I Vacuum force factors (vacuum created by a "flow through" liquid)

Greetings all, I'm new here and hope I'm asking this in the correct thread. So, the question is; where you have a vacuum created by a "flow through" liquid witin a large diameter container exerting suction force upon a smaller diameter input tube submerged in a liquid, does the surface area of...
35. ### Calculate surface integral on sphere

I'm supposed to do the surface integral on A by using spherical coordinates. $$A = (rsin\theta cos\phi, rsin\theta sin\phi, rcos\theta)/r^{3/2}$$ $$dS = h_{\theta}h_{\phi} d_{\theta}d_{\phi} = r^2sin\theta d_{\theta}d_{\phi}$$ Now I'm trying to do \iint A dS = (rsin\theta cos\phi, rsin\theta...
36. ### I Is it possible to have "ideal surface" whose highest peak is ~1 nm?

I mean you could buy a mirror or silicon wafer but they give say 0.5 nm or 5nm 'roughness' which I suspect is the mean average roughness but this doesn't rule out a high "bump" way above the mean average such that for example 1 million bumps of 1 nm and just one of 5 will result in...
37. ### B Speed of Point on Expanding Sphere

Suppose we have an expanding sphere. That means that the surface ##4 \pi r^{2}## is getting bigger and bigger. For example, suppose the area expansion rate is ##b \, r##. Does this limit the speed at which a point can move on the surface?
38. ### Surface Tension: Plate-Water Interface

I would think that a force due to surface tension would act upwards on the plate and not downward, as shown in the diagram I have come up with. The surface of water would act as a stretched membrane and therefore there would be a surface tension on water surface in contact with the bottom of the...
39. ### Why are the three different surface tensions in the directions shown?

I think in the explanation below a very small element of the liquid at the line of contact between the horizontal solid surface, air outside the liquid and the liquid itself is being taken, and forces acting on such a small element are being shown. This very small element is to the left of shown...
40. ### Work, Power and Energy — Lifting a coiled rope up off a surface

The solution said that Average power= net change in energy/time, but why is that true? If you have a different way of solving it, it would be helpful too
41. ### Average Electric Field over a Spherical Surface

The picture above shows the integral that needs to be evaluated, and the associated picture ## \cos\alpha ## can be obtained via the law of cosines. I'm simply confused as to where the ##\cos\alpha ## comes from in the first place. I just don't see why ##\cos\alpha ## is necessary in this...
42. ### I Can surface plasmons be used to build GeV gamma-ray lasers?

I read a paper about coherent surface plasmon amplification by free electron pumping in an article a few days ago. It seems to work as some kind of free electron laser-like light source, and I wonder how high the energy of photons can go in this way. Also I read in another paper about...
43. ### B Idle Photons (motionless relative to the Earth's surface?)

Can a photon ever be motionless relative to the earth's surface? Did it accelerate from 0 mps to 186,000 mps?
44. ### I How to flatten the surface of a viscous gel?

I have gel which has a specific gravity of about 0.8 and a stated viscosity of 25000 mm2/S (whatever that means). It's thicker than honey. It just sits there with an uneven top surface. About 20cc are in a container and I want to flatten the surface. The best I can do is to shake the container...
45. ### I Parameters of the rough surface (for electromagnetic scattering)

Dear friends, I will be grateful if anyone can help me I study electromagnetic scattering by rough surfaces for a certain case. Each rough surface can be specified with the statistical parameters sigma (σ) and correlation length (lc). while writing my manuscript I drew a schematic...

47. ### Trying to understand alveolar surface tension

Hello, I learned recently about alveolar surface tension, and the explanation provided in the course was not satisfactory, it said that it is due to the force that pushes water molecules of the outer layer to the inner layers, I don't understand why this force that pushes water toward the cell...
48. ### Surface density of stars in a Galaxy

a.) The scale length of the disk is the length over which the surface density of stars decreases by a factor of e. In this case, the surface density decreases by a factor of 10 over a distance of 9 kpc, so the scale length is 9 kpc. The surface density of stars at a radius of r from the center...
49. ### The maximal normal force (Friction with slanted surface)

The problem that I immediately ran into was how I would calculate N without knowing Fmax. I didn't think the y-component of N would simply be the same magnitude as mg. After being stuck for a good while I even tested if it was, by dividing the magnitude of mg with cosθ, which of course ended up...
50. ### I Tangential electric force at a surface

Suppose you have an infinite plane of charge. If the surface charge density is uniform, would the tangential electric force always be zero, even if it is not a conductor nor static? My thought process for this is that if you look at each point charge and draw the electric field lines, then at...