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. L

    Contact between skewed cylinders

    Hi, when two cylinders in contact, but not parallet to each other (skewed), are rotating, there is a development of forces between them which tends to push one cylinder along its rotation axis and the another one to the opposite side. In other words, there will be translation movement between...
  2. C

    How Does Refractive Power Affect Vision Clarity at Different Distances?

    Homework Statement A student is reading a lecture written on a blackboard. Contact lenses in her eyes have a refractive power of 57.50 diopters; the lens-to-retina distance is 1.750 cm. (a) How far (in meters) is the blackboard from her eyes? (b) If the writing on the blackboard is 5.00 cm...
  3. 2

    What Lens Power Does a Student Need for Reading Close-Up Without Contact Lenses?

    Homework Statement Without her contact lenses, a student can focus an object located 0.80 m to infinity from her eyes. The power lens, measured in diopters, is the reciprocal of the focal length, measured in meters. Assuming that the image distance in the eye is 0.02 m, what lens power does...
  4. S

    Understanding Dark Fringe at Contact Lenses

    Homework Statement I'm unable to understand the production of dark fringe in the central point of contact of lens.The text says "the path difference between the rays reflected at the top & bottom of air gap at the point of contact is zero.Actually the ray reflected from the top of air film...
  5. S

    Charge Equality Between Different Size Pith Balls

    Suppose you let identical pith balls come in contact to make q1=q2. Would the charges be equal if the pith balls were of different size?
  6. C

    Calculating Time of Contact for Hammer and Nail

    Homework Statement A 1.2- kg hammer hits a nail at a speed of 15 m/s and rebounds at 60 percent of that speed. The resisting force of the nail is 9000 N. Approximately how long is the hammer in contact with the head of the nail? Homework Equations P=mv Pf-Pi=Ft The Attempt at a...
  7. D

    Calculate the average force on the ball during contact

    Homework Statement A .145 kg pitched baseball moving at 35 m/s strikes a bat and is popped straight up (forming a 90 degree angle)to a height of 55.6 m before turning around. If the contact time is .50 seconds. calculate the average force on the ball during contact. Homework Equations...
  8. F

    Where is contact made during collisions?

    If two objects collide with each other, where is contact actually made? This question confuses me because even at the atomic level (two atoms colliding) where is contact made? P.s. i hope I'm in the right section of the forum
  9. T

    Mathematica Mathematical Demonstration - Lenses in contact

    Hi, I have been working on this for a little while and think I am approaching it incorrectly. If someone can help, I'd really appreciate it. This is for a basic introductory calculus based Physics class that I am in. 1. Mathematically demonstrate the following equation with no numerical...
  10. A

    Solving a Skiing Problem: Finding the Angle of Loss of Contact

    Ok so the question is, "A skier of mass 60kg, initially at rest, slides down from the top of a frictionless, icy, hemispherical, mountain with a radius of curvature R of 100m. a)Draw a free body diagram and write the Newton's Equations at the moment when he/she is at some point below the...
  11. L

    Foot Contact Time: Resources & Info

    Does anyone have resources for how long a foot is in contact with a football. Numbers I have found, but video or set of pictures with time on it would help. Please and thank you.
  12. M

    Tennis ball hitting a wall and rebounding - contact force

    A 57.0 g tennis ball with an initial speed of 25.2 m/s hits a wall and rebounds with the same speed. The figure below shows the force of the wall on the ball during the collision. What is the value of Fmax, the maximum value of the contact force during the collision, if the force is applied for...
  13. S

    Force Relationships: P + C = W

    A woman is straining to lift a large crate, without success. It is too heavy. We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person, C is the contact force on the crate by the floor, and W is the crate’s weight. How are the magnitudes of...
  14. Y

    What is the magnitude of the contact force between the boxes?

    I'm really confused about this problem - As shown in Figure 5-22, a force of magnitude 7.50 N pushes three boxes with masses m1 = 1.30 kg, m2 = 3.30 kg, and m3 = 5.10 kg. (a) Find the magnitude of the contact force between boxes 1 and 2. (b) Find the magnitude of the contact force...
  15. K

    Verifying Newton's Laws: Finding Acceleration & Contact Forces

    Hi I have a problem and a doubt regarding Newton's laws of motion. Consider three blocks of 5,2,5kg respectively placed one over the other and dropped from the top of a tower. (the 5 kg if at the top, 2kg in the middle and the 5kg at the bottom). i) Find the acceleration of each block...
  16. M

    Estimate Collision Duration: 1.5 N Force on Plastic Box

    What is the best way to estimate or measure the duration of a contact in a collision? I have a stick applying a 1.5 N force onto a stationary plastic box. Assuming that the plastic is incompressible, how long will the time have elapsed before the stick with 1.5 N no longer has an effect on...
  17. Z

    Liquid drop contact angle: THF, mica & graphite

    This is a long shot, but maybe someone will know or can point me in the right direction. I'm looking for an experimental value for the contact angle between tetrahydrofuran (THF) with both mica and graphite substrates. I've done numerous googling and also did a search on the web of knowledge...
  18. S

    Is friction independent from area of contact?

    Now, my textbook says that force of friction is independant from the area of contact. But, when the tyres of my bicycle get deflated i have to exert extra force than otherwise. Why?
  19. T

    Contact force in an ideal situation

    Assume I am holding a bar parallel to the ground. I let go of the bar and it lands on something at an arbitrary point on the bar before it hits the ground. How much force is dealt to the object (and bar)? This is the problem, but I'm going to simplify it to make a calculation possible. First...
  20. N

    Wearing Multiple Contact Lenses: Is it Safe?

    Is it okay to wear more than one in each/either eye?
  21. P

    How can I contact a University for funding for a project.

    How can I contact a University for funding for a project. The project is on fuel cells, and I plan on building two prototypes; one following the instructions precisely, the other for experimenting with nickel catalysts. I have a estimate of $75-$100 CDN. Thanks for any help, Pierre.
  22. L

    Max Speed to Maintain Road Contact over Bump

    I am having a hard time trying to figure out this problem: What is the max speed that you can drive the car over the top of the bump without losing contact with the road. I have the radius= 66.7 m, constant speed of car = 16.4m/s, and weight of your passenger=57.0kg. With these numbers I was...
  23. B

    Contact forces homework problem

    Hello, I have a problem and I would like to check my answers: A mass m1 rests on top of another mass m2 , which in turn rests on a frictionless horizontal surface. A light cord is attached to m2 ,which is used to pull on it witha force F. a) Find the acceleration ofeach object when...
  24. J

    Astrophysics - Can there be a contact binary from white dwarfs

    Question: A typical white dwarf has a mass of 1 solar mass and a radius of 10 thousand km. A typical neutron star has a mass of 1.5 solar masses and a radius of 30km. Given that there's a natural speed limit in Nature, namely the speed of light, is it possible to have a contact binary...
  25. L

    Contact between two rings or two cylinders

    Hello, I would be interrested in comments, references, books, papers and web pages regarding the problem of mechanical contact between two rings. The attached picture describes the geometry of the problem: a ring (tube) is resting on the bottom of a larger ring (tube). These two rings are...
  26. L

    How to Calculate Deformations and Contact Pressure Between Two Mechanical Rings?

    Hello, I would be interrested in comments, references, books, papers and web pages regarding the problem of mechanical contact between two rings. The attached picture describes the geometry of the problem: a ring (tube) is resting on the bottom of a larger ring (tube). These two rings are...
  27. G

    Which direction does the normal contact force act?

    A ring of mass 0.3kg is threaded on a fixed, rough, horizontal curtain pole. A light inextensible string is attached to the ring. The string and the pole lie in the same vertical plane. The ring is pulled downwards by the string which makes an angle "A" to the horizontal, where tan A=3/4. The...
  28. M

    How Is the Average Velocity of 22 m/s Calculated in a Golf Ball Strike?

    A 50g golf ball is struck w a club. the ball leaves the face of the club w a velocity of 44m/s Pf = mvf = (50 x 10^-3 kg) (44 m/s) = 2.2 kg m/s From this I must find the contact time t = change in x /average velocity The change in x in the radius of the ball .05m The average velocity...
  29. C

    Contact forces and action-at-a-distance forces

    Contact forces and action-at-a-distance forces... Are all contact forces the result of action-at-a-distance forces? After all, surely it all boils down to electrostatic repulsions, etc? Thanks in advance.
  30. I

    How much radiation comes in contact with the martian surface?

    How much radiation comes in contact with the martian surface? where can i find more info on this? thanx.
  31. R

    Distinction between forces by contact and forces in distance?

    Is there any real distinction between forces by contact and forces in distance?
  32. R

    Find the maximum frequency for which the block and piston will be in contact

    A block is on a piston that is moving vertically with simple harmonic motion. a)At what amplitude of motion will the block and piston sperate if the period of the piston's motion is 1.18 seconds? b) If the piston has an amplitude of 5.12 cm in its motion, find the maximum frequency for which the...
  33. P

    Independence of friction and area of contact

    Can anyone tell me why friction does not depend on the area of contact??
  34. A

    Direct and Indirect Contact with electrical epuipment

    I have one Question to ask Explain briefly the Difference between direct and indirect contact with electrical equipment. [100 words] thnx
  35. L

    Calculating Contact Forces Between Blocks on a Frictionless Surface

    This problem seemed very straightforward but I've somehow missed something... Three blocks (M1, M2, M3) are in contact with each other on a frictionless, horizontal surface. A horizontal force is applied to M1. If M1= 1.67kg, M2= 2.67kg, M3= 3.78kg, and F= 16.1 N: a) what is the...
  36. W

    Liquid Crystal Contact Lens: The Future of Vision Correction?

    Would it be possible that Opticians will be selling to visually impaired people, Contact Lens, made from a material that has a negative index refraction, that theoretically could be altered with a Liquid Crystal "Eye-Drop" solution? Basically how far are we from a Liquid Crystal Contact Lens...
  37. A

    Behavior of two liquids in contact and a boundary

    Hi, I have a problem that talk about the behavior of two liquids in contact and a boundary that appears between them. I am lack of theory about this situation do anyone of you could help me to find some paper of articles that talk about this? Thank you, Aron
  38. T

    When I made first contact with the alien I was amazed

    When I made first contact with the alien I was amazed by how different it looked, even though it's basic shape resembled mine. For example, we both had 2 arms and 2 hands, but the alien's hands tapered into only two digits on one hand and three on the other. I tried speaking to the alien, I said...
  39. K

    Jerk of the point of contact of a ball rolling on a flat surface

    Hi, I'm working on a kinematics problem of rolling a golf ball on a flat plane (4-position infinitesimally separated solution). The solution sought is to be planar, so we're working in 2D only. This is largely irrelevant though, as I'm facing a rather undergraduate puzzler. I need to...
  40. Ivan Seeking

    When first contact is made

    http://www.popularmechanics.com/science/space/2004/2/when_ufos_arrive/index.phtml
  41. Nim

    Electrons you come in contact with

    If you tap on a desk, or are walking, does that energy that is being transferred cause electrons in the desk or ground to jump oribitals and emit infrared light? Also, I've read that electrons never touch each other, and that there is actually some space between you and everything that you...
  42. P

    The advantages of contact with aliens

    Given the relativism (conjecturism?) involved with the hypothetical existence of advanced humanoid worlds far older than ours (on a scale of perhaps billions of years), is it not feasible that our inclusion into this "Galactic Club" would give to humanity a significant evolutionary boost...
  43. Sonty

    What is a contact transformation according to Dirac's Lectures on QFT?

    During the last week I've been reading Dirac. I browsed through his Quantum Mechanics and now I'm reading his Lectures on QFT. In both I found the term "contact transformation" and it seems he's the only one to use it because a few people at the faculty have heard about it but they can't give...
  44. R

    Matrix string theory, contact terms, and superstring field theory

    A recent paper details some new insights for the second quantized string field theory. This has some implications for future models, it appears to be quite sound, but this is based on a confined early viewpoint of a first once over reading, no doubt there will be more questions to follow...
  45. G

    How i can contact michio kaku?

    does anyone know how i can contact michio kaku! it would be the best
  46. wolram

    Exploring the Mysteries of Contact Binary Stars

    how can (contact binary stars) exist? why is it that one does not destroy the other? where is there center of gravity?
  47. D

    3 Scenarios: How & Why Make/Not Make Contact?

    Greetings ! 3 basic scenarios for you to consider and respond : 1. They come to us. 2. We come to them. 3. Our starships "bump into" each other. Questions : Would you make/not make contact - How ? Would you make/not make contact - Why (for them too) ? (Are you one of "them" ? )...
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