What is Contact: Definition and 448 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. tellmesomething

    Please help with this suggested solution involving electrostatic press

    My teacher gave us this idea: He told us that the contact force due to one halve on the other halve and the electrostatic force will balance each other. Therefore they'll be same in magnitude so use the former to get the answer However i do not understand how they will be equal. Intuitively it...
  2. shea

    Bug 'Contact' page broken

    I have tried on different machines and browsers (Edge, Chrome, Firefox, Safari); the latest upgrade of Windows 10, as well as up-to-date MacOS 14. When clicking the 'CONTACT' button in the footer bar, I do not seem to be logged in on that page. Trying to click 'LOG IN' in the header bar on that...
  3. Ahmad anbar

    Difference between contact pattern and mounting distance for a pinion gear?

    Hi What is the difference between contact pattern and mounting distance pinion gear . Is it possible for one to cancel the other?
  4. G

    I Moment of inertia and contact force

    Two rotating cylinders are held in contact by a force F1. The force is applied through the center of one of the cylinders. One cylinder is the driving cylinder and the other is the driven cylinder . Does the moment of inertia of the system depends on the force contact force F1? Why? And...
  5. Rikudo

    Where will the masses lose contact?

    In order to solve this problem, we can make use of energy and momentum conservation to solve this problem. But, I'm currently having a difficulty to find out where exactly plate B will lose contact with A. Here is what I'm thinking. First, B will collide inelastically with A, and then they...
  6. M

    A Confusion of the scale of contact line dynamics and capillary flow

    I'm having some trouble getting my head around the scale at which capillary flow and contact line dynamics are important. In the simple case of liquid rise in a capillary tube, a smaller tube will allow for greater rise since a larger height is required to achieve an equal weight of the liquid...
  7. ROOT0X57B

    Is the Hertzian Contact Model Suitable for Simulating Car Braking on Wet Roads?

    Hi there! First of all, I do not have a clear homework statement or relevant equations to give but I still put this thread in here because it's related to school work and I've previously got a warning for not doing so. I'm a french student who is going to start his second year after high school...
  8. A

    Engineering Hertz contact problems of three cylinders

    Greetings i´m trying to find the Force applied by the upper roller to calculate the contact surface. Here is indeed my solution 2*FR1* cos31,38=F=1500N FR1=878,57N (which is wrong the correct solution says 818,1N) FR1 is the force normal to the surface of contact. any help would highly...
  9. W

    How can you make Ohmic contact with NiSi in semiconductors?

    How NiSi is ohmic contact? Ohm contact occurs when a semiconductor has a lower work function than a metal, doesn't it? NiSi has a larger work function than Ni, so how do you make ohm contact?
  10. Kamuna

    Engineering Regenerative Rankine cycle with one contact feedwater heater

    My question is how do i get : A. required steam generated from the boiler per hour B. extracted steam per hour for feedwater heater C. thermal efficiency of the cycle I can solve the thermal efficiency but A and B is giving me difficulties, i know when solving the extraction of steam needs mass...
  11. Lay1

    Finding the acceleration of the ball in contact with the ground during bouncing

    the v before hitting the ground immediately=4.85m/s the v after hitting the ground immediately= 3.96m/s I considered the down positive, then v= u+at 3.96= 4.85+ (a*0.16) so a= -5.56m/s*s The answer is 55m/s*s The parts that I don't get are why it must be -3.96 and why that velocity becomes...
  12. rudransh verma

    Contact and electromagnetic force

    I don’t know what is contact force. Are friction and normal forces called contact forces? And we have to take the resultant of the two to get the net contact force?
  13. curiousPep

    Hertzian contact pressure & shear stress

    Hello, I am trying to get some intuition about the direction of the shear stress caused by the Hertz contact pressure. Once I exert some pressure downwards on a spherical object the direction of the Hertz pressure will be upwards. However, this case some shear stress to exist, but I can't see...
  14. J

    Points of contact and contaminations

    My small blanket fell into the floor with a dry floor mat on it. I'd like to know what kind of contamination can occur here. That is, do only the dusts in the dry floor mat transfer to the blanket? Can the dusts be removed just by moving the blanket fast up and down? Or could there be bacterial...
  15. greg_rack

    I Exploring Acceleration at Contact Point Between Wheel and Surface

    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...
  16. curiousPep

    Engineering Contact mechanics - Thrust bearing

    Hello, I am doing some contact mechanics and I had an example in my Lecture notes about a simple thrust bearing with three balls where the bottom plate is stationary, the top plate rotates with angular velocity w, and the cage rotates with angular speed Ω. It says by inspection Ω =w/2 but I...
  17. FEAnalyst

    Hertz contact stress with prescribed displacement

    Hi, one can easily find formulas for Hertz contact stress in various cases (two spheres, two cylinders and so on) when force is applied to one of the bodies. But how to get the equivalents of those formulas when prescribed displacement is used instead of stress ? For example, I’ve found this...
  18. bhobba

    COVID Will a High Vaccination Rate Affect Contact Tracing?

    I heard an immunologist say the other day that once a high vaccination rate is achieved, contact tracing will likely not be effective. I can sort of understand why. Does anyone from places with a high vaccination rate know if contact tracing is still an effective measure? It is very widely...
  19. Uchida

    Dynamics motion problem with a disk in contact with a bar

    First, I tried to model the disk-bar as a crank connecting rod, to the OA bar, and apply this: VP = VB + ω_BP x r_P/B, where P is the contact point between the disc and OA bar. I assumed VP = VP sin 30º i + VP cos 30º j (direction parallel to r_P/B), where r_P/B = sin 30º i + cos 30 j This...
  20. Pipsqueakalchemist

    Engineering Zero Velocity & Acceleration of Point of Contact: Problem Explanation

    For this question the ball is rolling without slipping so that means the velocity of the point of contact is zero. Does that also apply to the acceleration of the point of contact? Because that’s what I assumed and I applied the relative acceleration formula above and use the starting point to...
  21. Pipsqueakalchemist

    Engineering Crate lowered by two ropes and deceleration at each point of contact with rope

    For this question, I don’t understand the steps for the relative motion part. When I try it I get angular acceleration to be zero which is obviously wrong. The solution doesn’t consider the Y distance between G and A but I don’t understand why. In the relative motion equation it’s suppose to be...
  22. W

    WhatsApp : Adding International Phone for Contact

    Hi All, I am trying to add a new contact from WhatsApp that requires an international phone. I have done this a few times without problem, but that was way back. Now when I enter the contact and try to call, I get an error message to the effect that the number cannot be reached. I've been...
  23. E

    B Gas Interaction in a Box: Force and Pressure Dynamics

    There is a box ##\mathcal{B} \subseteq \mathbb{R}^3## with a partition coinciding with the plane ##z=0##. The gas in the region ##z<0## is initially at ##p_1## and the gas in the region ##z > 0## is initially at ##p_2##, where ##p_1 \neq p_2##. At time ##t=0##, the partition is removed (details...
  24. V

    Analysis of a Frictional Contact Problem with Adhesion

    Hi, I'd to work with a model which represents a contact problem. I want to suppose that f_0=0 and f_2=0 where f_0 is a density of body forces and f_2 is a density of surface tractions . I am mathematician so I don't know if the hypothesis that I'd to suppose will make the problem have a sense in...
  25. P

    I Does the Normal contact force act through the centre of mass?

    Consider the following situation: You have 1 rectangular block lying on a table, and an identical block is placed above the block on the table. Now, this new block is constantly pushed to the right, right before it topples off. Consider the torque about an axis passing through the rightmost...
  26. Narzog

    Welded plastic safe for mouth contact?

    Hey guys. So I make pennywhistles. And its popular to make the heads out of acetal / delrin. So my question is, if I were to weld two parts together using a soldering iron or plastic welding tool, would it still be safe for mouth contact? My knowledge of this stuff is very limited. But from...
  27. A

    Speed for loss of of contact between a dumbbell and a table

    Attempted solution: Consider the instant when the normal force of the lower ball is zero. Conserving energy: $$\frac{mv^2}{2}+mgh_1=\frac{mv_1^2}{2}+\frac{mv_2^2}{2} + mgh_2$$ Applying the resulting torque to the upper ball where the rotation point is the lower ball. $$T=I.a =...
  28. Andrea Vironda

    Question about angular contact bearing mounting

    Hi, In my memories there's the information that in a O shaped mounting, the bearings will work in diagonal (the forces will be transmitted following that path). But in many drawings I can see the presence of a spacer between internal rings. Is it necessary since no force should be transmitted to it?
  29. M

    Is a Static Contact Angle Model Appropriate for Microgravity Fluid Simulations?

    Hi PF! I have an experiment where a wedge about 160mm long is in microgravity. I withdraw silicone oil from the wedge at a relatively slow rate (no turbulence). Since the wedge angle is small, a lubrication approximation is made. Inertia is shown to be low. I want to simulate this flow. When...
  30. K

    Different metals in contact with each other

    I learned in school that when two different metals come in contact with each other accelerated corrosion will occur. How about alloy and metal with painted surface? For example, I think that stainless steel is very unreactive / non-reactive. Could it cause any accelerate corrosion to itself or...
  31. S

    I Multiple Universes Coming into Contact

    Imagine there were two simultaneous Big Bangs, each producing an independent Universe, and well separated from each other at their formation. Presumably because each would have its own unique set of initial conditions and would follow its own development timeline, they would each have different...
  32. M

    Engineering Contact pontential for a semiconductor

    Anyone can help me, which formula I should use for this question?
  33. M

    Fluids: Kistler contact angle model

    Hi PF! I keep seeing Kistler's contact angle model wrote like this $$ \theta_d = f(Ca+f^{-1}(\theta_e)) : f = \arccos\left( 1-2\tanh\left( 5.15 \left( \frac{x}{1+1.31x^{0.99}} \right)^{0.706} \right) \right) $$, where the plot then has a sort of break, something like this: But this is not the...
  34. wrobel

    Two cylinders rotating with contact at an angle (reformulation of the problem)

    Some time ago there was a problem with the following picture somewhere out here. I think this problem was underestimated a little bit. Let us reformulate the problem. Assume that each cylinder, if it was not influenced by the other one, could rotate freely about its fixed axis. But the...
  35. J

    I How does contact occur at the atomic level?

    When we touch something, will there always be a layer of air between us?
  36. E

    Surface tension and Young's contact angle

    I came across this diagram, the ##\gamma##'s are supposedly forces per unit length of the respective interfaces: It's not clear what these forces are acting on. ##\gamma_{SL}## and ##\gamma_{LG}## look like they could be acting on a small bit of water right at the end, but I have no idea what...
  37. TimeDoctor

    Whom to contact about my improvement on telescope optics?

    Hey guys. If you have a prototype of a new telescope, whom do you contact? This telescope uses the same lenses that we have but enhances their power in a n^4 So, if you have a lense that is supposed to magnify things twice, it'll magnify them 8 times. I just don't know whom to contact or where...
  38. Ranger Mike

    What Is the Contact Patch Between a 0.5 mm Radius and a 3 mm Diameter Ball?

    Hello friends! What is the contact patch between a radius of 0.5 mm (0.020”) and a 3 mm (0.125”) diameter ball? All i can find is that it it a Point. And points have location not dimensions.
  39. Ryan_m_b

    Is Contact Tracing Without Personal Data Collection Possible?

    Thought the members here might like this explanation on how contact tracing apps can be made that collect no personal data. The design is quite clever at preventing situations where centralised databases collect information like who you are, where you’ve been, who you’ve met etc.
  40. S

    Do you think we should attempt contact with aliens?

    I would like to know your opinion about this. Do you think we should try to contact aliens? I think it's safe as long as we choose stars as old as the Sun or younger. I also think that, if a nearby civilization hasn't contacted with us yet, it's probably because they don't have the means to...
  41. jamiebean

    What is the contact force for a 20kg object with an acceleration of 2.7?

    I have watched a couple of videos regarding contact force, but I am still confused in solving this problem. which is its contact force? Fc=ma =20kg x 9.8=196N ?? then what's the acceleration a=2.7 for? im kind of self-taught right now.. my professor does not explain these simple questions...
  42. R

    Force acting on the contact area?

    Material - SS 316
  43. B

    Field Evaporation of Contact Charged Spheres: Exploring Possibilities

    If you were to positively contact charge a small ~1 mm diameter sphere using a Van de Graaff generator, and were to charge it sufficiently high enough that field evaporation began to occur, what would happen? Would the rate of evaporation increase exponentially as the field strength would...
  44. Heyxyz

    How Long Does a Box Stay In Contact With a Spring as it Bounces Off of it?

    T = 2π * √(2/300), T = .513 seconds. If I divide it by 4/3, I get a final answer of .385 seconds of touch. I know the box isn't attached for the entire oscillation, so T has to be divided. To me, it makes sense to divide it by 4/3 (when the box falls, the spring is compressed, hits...
  45. Y

    Number of pins? & Point of contact?

    Hello.. I am confused in two questions. First one is i am designing 1 pin shaped which can mould the free form surface. i am confused in different type of shapes pin like circle, square, triangle..etc.. My question is if i am moulding a free form surface by these shape of pins which shape will...
  46. R

    I Metal Semiconductor contact (Part 2)

    MOS (p type) 1) Figure a) and b) are the cases of strong inversion. Figure b)-For high frequency signals, electrons at the semiconductor oxide interface do not get enough time to change ( I follow that ), but how come the charge in the bulk close to the depletion region changes with these high...
  47. R

    A Understanding the Charge Distribution at the Metal-Semiconductor Interface

    Assume n type semiconductor: 1) Can the fermi level of metal change when it makes contact with the n type Semiconductor ? What assumptions do we make in ideal situation ? 2) Is the Schottky Barrier in Metal Semiconductor contact remains constant with an applied forward or reverse voltage ? 3) On...
  48. PhysicS FAN

    The motion of 2 objects in contact

    For the non-circular object of mass m: From Newtons second law we get that F-N-T=ma where N is the force that the cylinder acts on the object. Replacing numbers: 13-N=2a. For the cylinder: From Στ=Τa(ang) we get that T'= 1/2ma or T'=a. Where T' is the friction that acts on the cylinder and we...
  49. atommo

    Limit to generating static electricity via contact?

    Let's say you are rubbing a balloon on your hair to make it charged. If you then discharge the balloon and rub it on your hair again (and repeat this process numerous times). Would your hair run out of electrons so eventually you would be unable to charge the balloon, or would your hair gain...