What is Contact: Definition and 447 Discussions

Contact dermatitis is a type of inflammation of the skin. Some symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, and swelling. The rash isn't contagious or life-threatening, but it can be very uncomfortable.
Contact dermatitis results from either exposure to allergens (allergic contact dermatitis) or irritants (irritant contact dermatitis). Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight. Diagnosis of allergic contact dermatitis can often be supported by patch testing.

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  1. T

    Frictional force and surface area in contact

    I've read that the surface area of an object in contact with the ground doesn't not affect the frictional force acting on it as it is pushed forward. I kinda understand what is explained but I find it difficult to reconcile with what happens in real life... Don't wheels reduce the surface...
  2. V

    Contact analysis in Flexible gear

    Hi everybody, I'm working on an analysis model of flexible gear in ANSYS workbench. This model has 3 components: flexible gear(FG), wave generator(WG) and rigid gear(RG) Applied force have two case: WG makes FG deforming from circular shape to ellipse shape, the FG contacts and engages to RG...
  3. Noisy Rhysling

    Favorite "First Contact" scenario?

    Again, I'm going with the Motie, because the idea of stripping down to allow the aliens to inspect a human body could only be trumped by having the only woman in a whole lotta miles do the same, for instructional purposes.
  4. K

    Prolonged contact between HCl and alkanes

    I've verified that there is no obvious reaction between hydrochloric acid and simple alkanes (roughly C4-C12) over short timescales; they simply settle out with the heavier HCl on the bottom and the lighter hydrocarbons on the top, with no apparent heating or changes in general properties (as...
  5. C

    Contact area of ideal sphere resting on flat surface

    Greetings All, I have a rather odd question which has been bothering me. If you have a perfectly round sphere sitting on a perfectly flat plane, what is the area of surface contact between the two? Is there an actual value, or is it something which can't be calculated. I'm assuming the diameter...
  6. A

    Measuring contact angle of immiscible liquids

    I am looking for sources which describe how to measure the contact angle between immiscible liquids in a tube. The literature seems to be extremely lacking so if anyone has any knowledge I would appreciate the help.
  7. A

    A Contact Angle of Immiscible Liquids in a Tube

    I'm having trouble finding any sources which describe how to accurately measure the contact angle between immiscible liquids in a tube. Any help would be appreciated.
  8. O

    Best domains of astronomy to contact super-advanced E.T.?

    Hello.If one’s goal was to contact a technologically superior extraterrestrial being (or a group of beings, or a civilization), which domain(s) of astronomy should one specialize in precisely?1) Which type of astronomy should one specialize in? Computational astronomy Experimental astronomy...
  9. Nate0331

    Electromagnetism and injury -- physical contact at the molecular level....

    So here is my question, and maybe I am not asking it right, but here we go: If electromagnetism prevents me from actually touching anything at a quantum level, how is it that I can get cut by a knife, or get a road rash falling off my bike? If the negative field of electrons that surround...
  10. carb

    Contact pressure - screw pretension

    Hello, I'd like to calculate the max contact pressure in the below assembly, just before contact loss between the beam and the wall. The beam is clamped to the wall with a pretensioned screw, and sustaining a force at his gravity center. I'm assuming all bodies dimensionnaly stable (no...
  11. H

    I Normal contact force for a sliding slope

    For the following question, how do we know that the acceleration of ##M## is constant over time? And is the normal contact force between the two masses smaller as compared to that where ##M## is fixed? The acceleration depends on the net force on ##M##, which depends on the normal contact...
  12. L

    Contact Force with two masses given

    Homework Statement A 3.0 kg and a 5.0 kg box rest side by side on a smooth, level floor. A horizontal force of 32 N is applied to the 3.0 kg box pushing it against the 5.0 kg box, and, as a result, both boxes slide along the floor. How large is the contact force between the two boxes? a) 32N...
  13. I

    Contact potential difference

    Homework Statement Hi! I'm writing my lab report on the Franck-Hertz experiment and I have trouble with the contact potential difference (inelastic collision). How do you calculate it? Homework Equations See below The Attempt at a Solution The energy differences between the maximum and...
  14. C

    Reflections of Light in Contact lens

    It is said that whenever index of refraction varies, there are reflections and it can reach 4% for uncoated surfaces.. how about in thin contact lens used for eyes.. is there also 4% reflection on each surface if they are uncoated?
  15. G

    B Quantum Model of Contact Forces

    I'm curious about contact forces, such as the normal reaction force on a book resting on a table. I've read that it's actually the electromagnetic force, but atoms are electrically neutral and there is no ostensible repulsive force between electrons and the nucleus, so I have some doubts. Has...
  16. kolleamm

    Robotics, how to detect contact with objects?

    I have a robotic arm that needs to be able to detect whether or not it bumped into something like a wall. What would be the most practical way to do this without adding a large amount of sensors in different parts of the arm?
  17. S

    Rolling without slipping taking the contact point as pivot

    I'm confused about this rolling without (or better with) slipping situation. Suppose to have a disk with initial velocity ##v## and angular velocity ##\omega##. The motion is to the right but the angular velocity is counterclockwise. There are no forces acting on the disk besides the kinetic...
  18. P

    Who does the ordinary man contact?

    hi unlike probably every one else on this forum, I am neither a scientist, a student, nor a teacher. What I am is very interested in theoretical physics. Any way what I would like to know or would like help with is where or who I could approach with a theory on dark matter/ energy which...
  19. Jesper Hellmann

    Contact Stress Problem: Validate Nylon Clamp & Steel Tube

    Hi All I am trying to validate a nylon (PA6 Guss) clamp which has a load of 166kN on a steel tube. I am only interested in validating the clamp. My analytical (MatLab-Octave) calculations give me a peak Von Misses stress of about 145MPa When comparing to FEM in ANSYS I only get about 30MPa Can...
  20. R

    How is the integral expression for contact time derived?

    Don't know if this is the correct place to post this, this is not an assignment question, but I am terribly stuck with this. While going through the derivation of contact time for a hertzian contact as given in problem 3 at the following link http://s17.postimg.org/t1kq6mlxr/Capture.png , I am...
  21. S

    ANSYS workbench moving plate contact

    Hello, I am trying to make contact between a stationary line body and a moving plate that will compress the line body. But I could not make contact between them. There is also a automatic connection generated but while simulation it does not show the contact instead the moving plate...
  22. rjbeery

    What is the definition of physical contact?

    We talk about local effects and surfaces being "in contact" with one another but do we have a vigorous definition for such a state? The objects reach a distance where their repelling EM charges resist and balance against a given force (such as gravitation)...but increased charges would make...
  23. Racer_Rob

    Free body diagram for a sliding contact

    Homework Statement Component A is pushed vertically down with a known force F into component B. The angled surface of B is parallel to the angled surface of A. The contact between A and B is rough and so is the contact between B and the ground. The coefficients of friction are known and so is...
  24. R

    Difference between ohmic contact and schottky contact

    Hi guys!, i want to know the advantages/disadvantages of using ohmic contact and schottky contact, because i will fabricate a photodiode (p-n junction) and lot of the articles say that ohmic contact is the best for this kind of device. But schottky contact rectify the signal which is more...
  25. S

    Why is air-water contact angle usually assumed to be 0 ?

    I am a Ph.D student currently interested in fluid flow in porous media (rocks in my case). I am currently trying to find the range of values for the contact angle in air-water-sandstone systems at shallow reservoir conditions (say 7.5MPa and 35 degrees C). The only value I have managed to come...
  26. W

    Can ANSYS Analyze the Difference in Gap Values for Contact Surfaces?

    I'm an intern currently and doing some analytic project in a company. So i am required to determine the gap between 2 contact surface (2 O-rings). I've obtain some result by using "node to node" contact with some commands and also probe "gap". There's some difference between the results and the...
  27. gracy

    Problem related to two conductors in contact

    Homework Statement An isolated conducting spherical shell carries a negative charge. What will happen if a positively charged metal object is placed in contact with the shell interior? Discuss the three cases in which the positive charge is a) less than , b) equal to, and c) greater than the...
  28. T

    Is Contact Force Responsible for Molecular Bending in Objects?

    Hello, When we have 2 bodies in contact with each other, for example a book lying on the surface of a table. The table's molecules bend a little bit because of the weight of the book thus producing the contact force. My question is this contact force acting on the book does also bend the...
  29. S

    Questions About Contact in the Movie

    Hello I am new here and my question is this: Spatially, what is the distance EM travels through space before redshift alters the wave to the extent that a radio signal becomes a microwave signal? Also when a radio signal containing information redshifts to the microwave band is the...
  30. J

    Moment of Inertia of multiple bodies in contact

    What is the overall moment of inertia of many cylinders in contact, where each is rotated about an axis through its center of mass. For example, a set of rollers. (See picture)
  31. T

    Why does friction remain constant with larger surface area?

    My books and my teachers tell me that the frictional force is independent of the area of contact. I am also aware of the equation F=μN and that area has no part in it. But it's just so confusing and counter-intuitive. Friction is because of the the interlocking of the irregularities of two...
  32. Hyo X

    Wirebonding - minimum contact area

    I am designing a mask for a chip which might be used for wirebonding. What is the minimum contact area for wirebonding using a microscope and microprobe? Currently my contact pads are 220 x 220 um. Is that big enough?
  33. ryanuser

    What is a Schottky barrier or contact?

    I looked at many websites including wikipedia and videos on youtube but I found them all very complicated and many contained diagrams that did not make sense to me. What is a Schottky barrier or contact in simplest form so that a 17 year old high school physics student can understand? Thanks
  34. M

    Why electrons never make contact with the nucleus?

    Hi everyone: This concept has bothered me for a while. The concept being that two oppositely charged particles (electron and proton) are attracted to each other, but the electrons go on a orbital trajectory around the nucleus instead of directly "sticking to" the nucleus. The closest I have...
  35. H

    Where can I find reliable sources for my paper on contact electrification?

    Homework Statement I'm currently doing a paper about contact electrification between insulators and I'm having trouble locating reliable and free sources for the said topic. I was hoping if any of you know a site that explains contact electrification and is decent enough to be presented as a...
  36. ohwilleke

    Understanding Fermi Contact forces

    Normally, you think about SM forces being conveyed by gluons, weak force gauge bosons, or photons (ignore that troublesome gravity thing for the moment) between point particles. There is also a property of fermions (particles with total angular momentum Q=1/2, 3/2, etc.) that they can't occupy...
  37. D

    Nitinol, how fast does it absorb heat in direct contact?

    Hello, I am new here and this is my 1st post. I want to know how fast does Nitinol absorb heat when placed in the following conditions: A soldering iron is heated at 310 degrees Celcius, and the tip makes contact directly with the electropolished nitinol. How long will it take for the nitinol...
  38. T

    Minimum velocity for particle to lose contact

    Homework Statement Homework EquationsThe Attempt at a Solution Honestly I have very little idea about this problem . The contact force has to vanish for particle B to loose contact .Not sure how to relate the velocity of upper particle with the normal contact force of the lower particle ...
  39. Hyo X

    Annealing Al/Si contact increases resistance?

    I'm trying to make an ohmic contact with p-type doped silicon. Using Aluminum. Under what condition of an Al/Si contact would annealing increase the resistance of the contact? or the silicon? two regions are defined using photolithography. A brief exposure to buffered oxide etch (6:1 H2O to HF)...
  40. J

    Another person trying to contact Kevin S. Brown (about typo)

    I suppose there's still no way to get in touch with the author of the interesting page http://www.mathpages.com/home/kmath633/kmath633.htm ? I want to inform him that the page contains the phrase "Large Hardon Collider". Sic. Actually, I'm mostly hoping he'll see this.
  41. R

    Contact pressure of piston rod onto a surface?

    I have two images below. This is a single piston with pressure inside, the variables are as listed. P_in = 2700 Pa. P_out = 0 Pa. R1 = Radius 1 = 10 cm. R2 = Radius 2 = 5 mm. P_contact = ? My solution to P_contact is as follows. Area A1 of piston at R1 = .0314m^2 and area A2 at R2 =...
  42. M

    How does annealing improves the ohmic contact?

    Suppose we have a p-type material and metal contacts deposited taking the work function of a metal and semiconductor into account. At room temperature (depending on the doping level) they might now show non-linear IV curve (non-ohmic behavior). How does annealing at higher temperature improves...
  43. gracy

    Case when there is no normal force in spite of contact

    Homework Statement "There is a pulley with 2 blocks on the table.Force "F" is acting on it ,as it can be seen here A=10 kg and B=20 kg F=294 N Now,my exact problem is my teacher says "there is no contact force between A and the table.." Why block A is not pushing against table while block B...
  44. gracy

    Normal Contact Force Explained: What My Teacher Says

    My teacher says In case (A) there would be normal contact force between the blocks.But in case (B)There will not be any normal contact force between the blocks. I am really not getting this.I think The normal force is the support force exerted upon an object that is in contact with another...
  45. S

    Point of contact of circle an tangent

    I want to find out the co-ordinate of point of contact of tangent to a circle from external point when its center and radius are known. Please Help me . . . Thank you in advance . . .
  46. Gordo

    Arc Suppression for Fuji PXR4 Micro Controller

    DPST Power relay has 120VAC coil & 40A contacts (resistive) ratings. A Fuji PXR4 Micro Controller is triggering the relay; the load is a 220V pottery kiln element. The contacts are arcing (but not bouncing) at make & break on nearly every cycle. The above relay just replaced a previous SPST...
  47. P

    Ohmic vs Rectifying Contact: N+ & N-Type Semiconductors

    Hello Every body! As shown in below, If i join a heavily doped n+ semiconductor with an ordinary n-type semiconductor, What is the type of contact that forms between n+and n-type semiconductors ? is it Ohmic contact or rectifying contact ??
  48. C

    Magnitude of contact forces

    Homework Statement Alex is asked to move two boxes of books in contact with each other and resting on a rough floor. He decides to move them at the same time by pushing on box A with a horizontal pushing force FP = 9.3 N. Here A has a mass mA = 10.6 kg and B has a mass mB = 7.0 kg. The contact...
  49. T

    Two cylinders in contact come to final angular velocities

    Homework Statement Two cylinders, made from the same material and having the same length,have radii r1 and r2with r1> r2. Both are free to rotate about their respective axes. The larger cylinder is initially rotating with angular velocity ωo. The smaller cylinder is moved until it comes into...
  50. Dennydont

    Total area of contact between tires and ground?

    Homework Statement A car has four tires in contact with the ground each of which is inflated to an absolute pressure of 3.1×105Nm^-2. If a person of mass 82 kg gets into the car by how much will the total area of contact between the tyres and the ground increase assuming that the tire pressure...
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