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. H

    Why does high contact ratio in gear result in inefficiency?

    As titled.This was taught to me in machine design, but I don't see how that makes sense I would think that doesn't matter how many teeths are in contact, since the force between gears are distributed on each pair of teeth in contact, more engaging teeth just mean the friction is distributed to...
  2. E

    Masses in contact with each other

    If 3 masses are in contact with each other I understand that the acceleration is the same for all if a force is applied to the first mass. Is the net force on each object also the same? Assume no friction.
  3. E

    What are contact forces, really?

    The four non-contact forces are explained with the help of different fields and their interactions. What about contact forces? Why does the door shut when I push it? Is it a simple transfer of momentum? If it is, do the electrons collide?
  4. D

    Transient - Contact Analysis in Ansys

    Hi all! I am trying to solve a transient contact analysis in Ansys 14.0 The problem is a Bouncing Rectangle problem. That's the procedure I use: /Prep7 k,1,-30,0,0 k,2,30,0,0 k,3,-30,30,0 k,4,0,30,0 Create->Areas->Arbitrary->Through Keypoints !Create the ground k,50,-20,30,0...
  5. M

    Point of Contact Between Arc and Circle

    Hello, I have an arc with an arc length = 46.88 mm and radius = 44 mm. I have an intersecting arc with an arc length = 26.69 mm and radius = 43.4 mm. A circle with radius = 24 mm fits between the two arcs. How can I determine the contact points of the circle and the two arc lines?
  6. I

    Contact interaction in Lagrangians

    Hi all, If I take an action involving two point particles coupled together by a delta function contact interaction is it possible to carry out the variation with respect to the fields? For e.g. S = \int dt \frac{1}{2} \dot{x}^{2} + \int \int dt \dot{x}(t) \delta^{D}\left(x(t) - y(t')\right)...
  7. R

    Friction direction of a set of contact points

    Assume that a box is motionless and is located on the floor ground (one box's face touches the floor completely). If we apply a force to this box such that the box keeps its motionless state, what we can say about the friction directions of all contact points between the box and the floor? Are...
  8. W

    Contact angle and anti reflective coating.

    Hi all, just want to ask is there any correlation between the contact angle of a anti reflective coating? i.e the bigger the angle, the better the anti reflective coating? Thanks in advance.
  9. J

    Electric force between objects that are in brief contact

    Homework Statement Two small charged objects of the same mass and volume are brought into brief contact with each other. If the initial charges on the two objects are -3.00 x10^-6 and -1.50 x10^-6, what is the electric force between the objects when they are separated to a distance of 0.500m...
  10. B

    What is the force of contact between the two blocks?

    What is the force of contact between the two blocks? Two blocks are in contact on a horizontal table. A force is applied on one of the blocks at a 30 degree angle (from the horizontal). The system moves towards the right. M1 = 2,00 kg and m2 = 1,00 km and F=60N and the kinetic friction between...
  11. C

    Maintaining eye contact when absorbing information?

    Hi, In general maintaining eye contact talking with people creates a sense of connection, but how do you feel about maintaining eye contact when listening to complex instructions? I often find it hard to maintain eye contact if an instructor is telling me something complex (such as...
  12. H

    Kinematic questions(velocity of 2 contact points)

    in the picture below http://tinypic.com/view.php?pic=9riq9l&s=6 if we know the angular velocity of the gear on the left, as well as their current distance from contact point, what can we say about the velocity of the right rod at the contact point at anytime t? we know it is not...
  13. K

    Bouncing ball exercise with time of contact with the surface given

    Hello. I have an exercise (not exactly homework, it's a physics contest that we are allowed to solve at home, using all possible help we can find) that goes like this: A ball with mass m = 0,10 kg falls vertically on a horizontal non-movable solid surface. Speed of the ball just before the...
  14. A

    Contact angle of liquid drop on solid surface.2

    Can anyone explain point 44 of the attached pdf document on surface tension. (Here's the link in case attachment doesn't work: http://www.sakshieducation.com/EAMCET/QR/Physics/Jr%20Phy/12Surface%20tension%20_198-208_.pdf How is the surface tension direction found out? {i know it...
  15. Q

    Is there a difference between contact time and impact time? (collsion)

    This is from my textbook: I'm slightly confused about the bit underlined in red. Do you think its in reference to the sentence just before where it talks about situations of vehicles remaining tangled? (so for other cases, contact time = impact time, right?) also, I don't really...
  16. A

    Two charged spheres are brought into physical contact with each other.

    Homework Statement Two charged spheres are brought into physical contact with each other. Initially, the charge on the first sphere was 2.34 nC, while the charge on the second sphere was -3.23 nC. a) What is the final charge (in C)on either charge?(2A) b) How many electrons moved...
  17. M

    Friction conditions on contact point of disc

    Hello, I have some doubts regarding the friction force on a certain situation. Imagine a disc over a fixed flat surface. Like this: The disc has two motions, rotational and translational but these are independent of each other. I mean the translational motion does not come from the...
  18. A

    Hand contact with capacitor negative (excess of electrons) terminal only.

    Thank you for any help you are able to provide. I myself think that the electrons will flow to the human body and further drain the battery.
  19. A

    Contact angle of liquid drop on solid surface.

    Can anyone explain point 44 of the attached pdf document on surface tension. (Here's the link in case attachment doesn't work: http://www.sakshieducation.com/EAMCET/QR/Physics/Jr%20Phy/12Surface%20tension%20_198-208_.pdf) How is the surface tension direction found out? Also why is...
  20. R

    Why involute gears have straight path of contact?

    my lecturer keeps saying that path of contact of an involute gear is straight line but without the reason. i can't digest it as i can't find the reason for this behaviour. I'm trying my best to find the reason. Internet too can't find an answer. Books don't give a timeline of how it happens. Can...
  21. T

    Help with Point Charges and Charge by Contact

    1. Homework Statement Three small identical metal spheres carry electric charges, +Q, +2Q, and +3Q. The centres of the spheres lie in a straight line at fixed positions R, S and T, such that the distance between the spheres at R and S is d1 and that between the spheres at S and T is d2. Assume...
  22. S

    Applying force to a flat object with contact points

    Hi all! This isn't actually a homework question, but thought this subforum is the place for this anyway. It's been some ten years since I last touched the topic of mechanics and I guess this is a real simple question, but what can you do when I don't get it! Any help is appreciated! How do...
  23. E

    Thermo Question: The math behind systems in thermal contact

    Hi! I am reading Molecular Driving Forces, 2nd ed., by Dill & Bromberg. On page 53, example 3.9, we consider why energy exchanges between two systems from the point of view of the 2nd law. We consider two separate systems. Each has ten particles, and each particle has two possible energy...
  24. A

    Rolling without slipping: Why point of contact has zero velocity

    In rolling without slipping, why does the point of contact have zero velocity relative to the ground? If so, how can the point of contact move relatively to the ground? (It has to move relative to the ground, otherwise it cannot roll and must stay in its original position)
  25. H

    What happens when a large amount of antimatter gets in contact with matter ?

    Hi everyone, I'm new to the forums and I don't have the knowledge you guys have about Physics, so my questions will be very simple. Yesterday I was reading a topic about using the antimatter as a weapon, and someone said it is impractical for many reasons, and he stated some, but only one got...
  26. J

    Small Body on a Sphere loss of contact

    Homework Statement A small body is set on the surface of a smooth sphere at an angle of 45 degrees from the center. At this point the sphere is given a constant acceleration in the horizontal direction of 9.8 m/s/s. There is more in the question, but the goal is to find when the body will...
  27. R

    Torque due to reaction force at contact point of two objects

    Hi there, I would like to know that if we have an leaning object supported by another object, both are supported by ground floor to satisfy static equilibrium condition, does the reaction force at the contact point produce cancelling torque (for the leaning object)? In general, can a reaction...
  28. D

    Forces Exerted on Objects in Contact

    Homework Statement Three boxes are stacked, one on top of the other. The mass of the top box is 4kg. The mass of the middle box is 3.5kg. The mass of the bottom box is 3.0kg. What is the force exerted by the middle box on each of the other boxes? Homework Equations Fg = mg The Attempt at a...
  29. nukeman

    Cranial Nerves: The cephalic level of contact with the CNS ?

    Cranial Nerves: The cephalic level of contact with the CNS...? Homework Statement I am having to list off the 12 pairs of cranial nerves.. But, I also have to list the following for each one. "The cephalic level of contact with the CNS (eg. telencephalon) where the nerves nuclei are...
  30. T

    If numbers are infinite in both directions, physical contact is impossible.

    This is a paradox that has been bothering me since I was taking algebra in high school. Let's say that I want to represent the distance between to objects. Given that numbers are infinite in both directions, by which I mean that there is no limit to how large, or small a number can be, there...
  31. A

    Determine the magnitude of the contact force between the two blocks.

    Homework Statement Two blocks of masses m1 and m2, with m1 > m2, are placed in contact with each other on a frictionless, horizontal surface. A constant horizontal force is applies to m1. a) find the magnitude of the acceleration b) determine the magnitude of the contact force between the...
  32. S

    HELP Calculating contact angle of benzene.

    Homework Statement In an experiment to determine how well benzene wets glass, benzene was found to rise to 1.71 mm in a certain capillary tube at 20.0 C. In the same tube, water rose 4.90 mm at 20.0 C. Calculate the contact angle for benzene, give that at 20.0 C, benzene = 0.879 gcm^-3...
  33. S

    Calculating Contact Forces- Three objects

    Homework Statement If you have a system with three boxes, two side by side and one on top of the first box and there is a horizontal force acting on the boxes, do you have to account for the third box in calculating the contact force between two of them? Say if box 1, box 2, and box 3 (three...
  34. M

    Principal curvature used in a contact problem

    Hi, I am trying to understand a theoretical problem involving the contact between two surfaces. I have uploaded a screen shot of the mathematical formulations of the solution. I understand most of the solution, except the principal curvatures. I have tried to look up principal curvature...
  35. C

    Achieving Uniform Contact with Silicon Wafer

    Hi all, I am currently working to build a Joule Heater that will be used to heat samples to upwards of 1000*C in seconds in vacuum. While the temperature and speed is definitely there, the contacts are always non-uniform -- making the data hardly repeatable. I am using a ~70mmx10mm Silicon...
  36. H

    Automotive Intermittent contact in rolling friction

    hey i had a bizarre thought, what if there is a road made with a very smooth friction less surface and a normal asphalt road, arranged alternatively, such that , half the time spend by the tire in one rotation is placed on the smooth side and the other half on the rough side, such that the tire...
  37. D

    Contact Point between a Rigid Body and the Surface it sits (Semi-Ellipsoid)

    Hello, I've been having trouble with a certain part of a homework problem. I wish I had posted this earlier so there would be more time! Anyway... The shape is a semi-ellipsoid (a Rattleback, in particular). Here's a good picture of what I'm talking...
  38. L

    Thermal Contact in Ansys WB14

    Trying to model a thermal contact between two faces. The plan is to get the heat flowing from the right part to the left part with a temperature BC on the right and convection on the left. At the moment the left part stays in the initial temperature so the contact obviously doesn't work. I...
  39. E

    Expansions and order of contact

    I am asking my mentor for my class about this question, but unfortunately the answers I get from her often take forever and do not always clear things up for me, so I hope someone out there in Physics Forum has a good way of explaining this to me. Here goes... The question has some...
  40. S

    Losing Contact With Logic: Examining the Thin Layer of Reason

    When ever I go trying to solve a problem, especially the ones that have my mind greatly diverge into many concepts, I seem to notice myself losing contact with logic. Its like a bad dream really. I find myself attempting to solve how I am solving a problem and so on. Or at least questioning what...
  41. J

    Oscillation - car losing contact with bridge

    Homework Statement See attachment Homework Equations The Attempt at a Solution Ok so as the bridge is at a point ABOVE eqm acceleration is DOWN and at some point ACC down is greater than gravity acceleration. This is all true but makes no sense to logically. How could the car...
  42. S

    Finding the contact force in a hinge?

    I have been working on a slightly tricky calculus problem and was hoping someone could verify my solution. Homework Statement A 4m long beam whose mass is 5 kg is attached to the wall by a wire and a hinge that allows the beam to rotate. There is a sign (with a mass of 20 kg) attached to...
  43. K

    Schools How to contact universities/research scholars for an apprenticeship in astrophysics?

    Hi, My name is Rupak Karnik. I am currently a third year student in electronics engineering in Mumbai, India. I have a very keen interest in astrophysics and space sciences and I plan to pursue a career in the same. I have a mid-semester break during the months of June and July for 6 weeks...
  44. R

    Thermal contact final temprature

    Homework Statement The following is a worked problem from my textbook: Consider two masses, with initial tempratures T1 and T2 are placed in contact and isolated from their surroundings. They are CV1T1 + CV2T2 = CV1Tf+CV2Tf This equation can be solved for the final temprature T_f =...
  45. J

    What is the Appropriate Term for the Contacting Surface on a Valve in the U.S.?

    Contact surface -- term Hello everyone! Help me please with selecting a correct term. The situation is as follows: There is a valve, which has a body and a bonnet. There is a joint that connects the body to the bonnet. There is a contacting surface on the bonnet flange and body flange...
  46. T

    Metal Contact Effect on 1-D particle in a box quantum well

    Dear All, When an electrical contact is made onto the quantum well, how would the energy states be affected ?
  47. S

    Electrochemical cell question - strip on Zn in contact with zn2+/CN solution

    The potential at which a metal is deposited in the electrowinning process can significantly affect the quality of the deposit. The potential itself can be dramatically affected by the addition of complexing agents and by adjusting the pH of the solution as the following calculations demonstrate...
  48. V

    Radius of Curvature at Soap Bubble Contact Point

    Two soap bubbles of radius r and R are in touch find the radius of curvature of their point of contact? (Both bubbles are touching each other with their external surfaces) I have no idea about this question. can you please try to help>
  49. R

    Gas liquid contact in stripping column

    \frac{x[Ain]-x[Aout][/SUB][/SUB]}{x[Ain]-x[out][/SUB][/SUB]}=\frac{\sum s^{K}-1}{\sum s^K} (1) for k = 0 to n Final result...
  50. C

    A cylinde with a piston in contact with a heat reservoir at 353 k.

    A cylinde with a piston in contact with a heat reservoir at 353 k. While keeping this gas at constant temp and pressure of 1.01 x 10E5 n/m2 we permit he gas to expand by 1.5E-5 m3. How much heat does the gas absorb? Is it just p x v = w and w = q to get an answer of 1.15 j? Cause i feel like...
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