What is Friction: Definition and 999 Discussions

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:

Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction ("stiction") between non-moving surfaces, and kinetic friction between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure 1).
Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other.Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces.Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy (that is, it converts work to heat). This property can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, for example when a viscous fluid is stirred. Another important consequence of many types of friction can be wear, which may lead to performance degradation or damage to components. Friction is a component of the science of tribology.
Friction is desirable and important in supplying traction to facilitate motion on land. Most land vehicles rely on friction for acceleration, deceleration and changing direction. Sudden reductions in traction can cause loss of control and accidents.
Friction is not itself a fundamental force. Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. The complexity of these interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis and the development of theory.
Friction is a non-conservative force – work done against friction is path dependent. In the presence of friction, some kinetic energy is always transformed to thermal energy, so mechanical energy is not conserved.

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  1. ohmyshoulder

    I Question about friction in situation where interface slip occurs

    Hello, I have question about friction at inteface between two component slip occurs at interface when external force bigger than friction force(= normal reaction force * static friction coefficient) After slip occured, component motion stopped and got new static equlibrium state In this...
  2. M

    Morin 3.7 -- Block sliding sideways on an inclined plane

    TL;DR Summary: In Morin 3.7 sliding sideways on a plane I used a completely different method than he did and got the correct answer is my method right The problem statement is as follows I split up the friction force into x and y components derived a diff eq for v_y in terms of v_x then took...
  3. T

    Block on top of moving slab, with a rough surface - When does v_b=v_s?

    For the first question I thought of using an energy balance, there is friction ##\Rightarrow \Delta E_m = -W_f##. Both at the start and at the end, the block has no velocity. Therefore ##E_{\text{initial}}= \frac 1 2 m_s v_{s,i}^2## and ##E_{\text{final}}= \frac 1 2 m_s v_{s,f}^2##. This means...
  4. aiqing

    Is it friction or tension acting on the person hanging on a rope?

    The first question statement was under the chapter ##Newton's Laws Of Motion (Without Friction)##. Whereas, the second question was under ##Friction##. The free body diagram for the first question is given as: And the free body diagram for the other question is given as: In the first...
  5. T

    Energy analysis of this system (curved ramp up and a spring)

    For point one it's clear that I have to use energy => ##ΔE_{AB} = W_{friction}## ; ##\frac 1 2 mv_0^2 - \frac 1 2 mv_1^2 = mgμ_d d## After that there is the path BC, but I don't know how to analyze it from an energetic standpoint. Then after BC the block will now have a different velocity, I...
  6. lost captain

    I Shouldn't the pressure difference along a pipe be a negative number?

    Across a horizontal pipe with fluid flowing inside, the pressure will drop due to the friction between the fluid and the pipe walls So if for example the fluid flows from left to right and we take 2 points: P1 (pressure on the left) and P2 (pressure on the right) then P1 should be bigger than...
  7. lost captain

    I How does friction in a pipe occur, with the "no slip condition" ?

    Hello everyone 😊 Let's say, we are having laminar flow in a cylindrical pipe. The fluid in direct contact with the pipe doesn't move (no slip condition), so there is no sliding between the surface of the pipe and the surface of the water. The friction that occurs is actually between this...
  8. T

    How can I determine the instant the block overcomes static friction?

    I know that the block will move only if the force that pushes him is greater than μs mb g. The only force that can act on the block is the elastic force (Fs) generated by the expansion of the spring, caused by the rolling sphere, that rolls because a force F is acting on the sphere. Then can I...
  9. S

    Find the coefficient of friction between block and surface

    Ff.x= mv2/2 - kx2/2 umgx= mv2/2-kx2/2 u= mv2-kx2/2mgx =
  10. Lotto

    B How will a spring stretch in the following cases?

    1) I have a spring on the ground with no friction and the spring is not attached from one end. If I apply a force ##F## and the spring is massless, will it stretch? I think that it won't. But if it has a mass ##m##, will it stretch now? Will it be ##x=\frac{F}{k}##? I don't know, but I imagine...
  11. chwala

    Calculate how fast the car was travelling when brakes were applied

    My query is on highlighted. This was straightforward. I thought that coefficient of friction ought to lie between ##0## and ##1## maybe i need to check that again anyway; ##F_{lim} = 1.5 ×15000= 22, 500 N## Using ## v^2 = u^2 +2as## and ##F=ma## ##22,500 = 1500a##...
  12. alomari

    Help with Friction Forces: Box resting on a board on a frictionless surface

    Hello, I'm struggling understanding why my answer to this question is incorrect. I know the right answer, but why is this way wrong? I have attached my solution and would really appreciate the help. Thank you!
  13. Q

    I Looking for a formula for damage when sliding to a stop

    The context is going down a hill in rollerblades: when people fall and they come to a quick stop (due to not having protective gear and there being lots of friction), they always end up with major injuries, while people with protective pads can sometimes fall and slide for 60+ feet and often be...
  14. M

    Tidal friction and global warming

    Ignoring global warming, the Earth will spin progressively slower. But how will global warming affect this? THEY say, LESS water, LESS slowing. > slowing spin is all about the FRICTION from the action of WATER on the LAND, when the water is gone the slowing of the spin will ceased (or at least...
  15. seonjunyoo

    B I have a question about energy & ignoring friction losses

    If the energy itself ignores loss resistance friction and the energy moves forward, can infinity go far at a constant speed?
  16. iceice655

    Normal force at the base of a ladder

    Hello, I was recently tested on finding the normal force at the base of a ladder leaning against a wall as well as its friction force. So this is the question from memory. Given: θ the acute angle between the ground and the ladder μ as the coefficient of friction between the ground and the...
  17. P

    Loss of atoms from the surface of the material: How does it work?

    Good morning! A question from a mere layman, so I hope you won't eat me :D Some time ago I read that every time one solid body makes some contact with another solid body, several billion atoms are lost from the surface of both the first and the second. On the Internet, I once read a post...
  18. PavithraSelvaraj

    I How Does Friction Function in the Movement and Turning of a Car?

    How can friction be responsible for all of these: stopping, moving and also turning a car? Does friction actually exist or is it something we assume because we don't know something about motion of objects? I have read a lot of discussions about friction and now it is a cloud of mess in my...
  19. J

    Pull-off force: hose, pipe, clamp

    Was surprised by a study recently where we tested 6 samples for pull-off force at a 10% reduction in clamp Torque and noticed negligible shift in results. Is it possible that at higher torque the clamp is deforming the pipe, reducing the surface contact (friction) between the hose and pipe? The...
  20. I_Try_Math

    Vertical Mass Spring System | Analyzing work

    Is there a typo in this question? Supposing there was no friction, the block would fall until the force of the spring was equal to ##mg = 2 * 9.8 = 19.6##, taking the upward y direction as positive. Since ##F_{spring} = -200y## and ##19.6 = -200(-0.098)##, the block would fall 9.8 cm. It's not...
  21. I_Try_Math

    Work done by friction on a hockey puck

    The answer key claims the answer is -0.9 J. By my math it should be -0.501 J, is that incorrect?
  22. SSJBLOOD

    Find the coefficient of friction and acceleration with masses given

    I tried to use the energy route but the acceleration was not a plausible one. It was just way too big.
  23. Juanda

    I Transmission of torque using friction

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  24. sroberti

    Fluid Dynamics: Maximizing Downforce Between a Robot and the Floor

    Good evening, all! Some quick background: I am working on a robot for a competition that strictly limits entry weights to 3lb. Robot speed & acceleration are highly desirable in this competition, so I have been focusing on ways to maximize my entry's performance. Drive motors for these...
  25. L

    Friction between tractor tyres and the ground

    So in (a) the answer is just mgsintheta. When doing (b), I got 8.44x10^3N to be the NET force the tractor must exert. Does the tractor not need to overcome its own friction as well? If so, shouldn't the equation be F_tractor = F_exerted - F_friction, and the question is asking for F_exerted...
  26. MatinSAR

    Pushing a block against the wall of an elevator that is accelerating

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  27. M

    Static vs Kinetic Friction on an Unbanked Ramp

    I used kinetic friction and did mgμ_k=mv^2/r. However, the solution is mgμ_s=mv^2/r. I am confused on why we consider static friction and not kinetic friction, thanks!
  28. D

    Friction Forces on 2WD vs 4WD Vehicles

    My answer for this question is d as every car has the same result for the force of friction since the normal and coefficient of static friction is the same. I cannot find an answer online so can anyone help verify this? Thank you.
  29. E

    I An ID-card sliding on a low friction table

    I hold my identification card on a low-friction surface by one of its edges. I slightly lean it, and it starts to fall. Before it falls over, I place my finger against the card, and this prevents it from falling all the way over. Then, I withdraw my finger without pushing or pulling the card and...
  30. Venturi365

    Relationship between horizontal force and friction in an exercise

    The thing with this exercise is that I don't think that the question makes sense at all (or, at least, is incomplete). First of all, we don't know if the mass moves with any of those tensions, therefore I cannot know which coefficient apply. Second of all, even if we suppose that the mass is...
  31. N

    Oscillation with friction - Analytical mechanics

    Hi, I had those exercises and want to know if they're correct. Also, feedback/tips would be great from you, professionals. $$A$$ 1. Let's consider the oscillator with a friction parameter... \begin{equation} m \ddot{x}+\alpha \dot{x}=-\kappa x \end{equation} but with \begin{equation}...
  32. O

    Capstan Equation, Friction and Normal Force

    We have a following setup (see below). A plastic rod is placed inside a plastic ring. A wire is wrapped around a plastic rod from which it goes to the outer surface of the plastic ring. The friction coefficient between the wire and the plastic ring is about 0.1. We have several different sizes...
  33. mazia

    Question(s) Regarding Magnitude of Force (Window Washer Problem)

    So, ignore the -0.72, I was just trying to see if I had a sign error (I then remembered magnitude is absolute value) but basically: Since the weight is 12.0N, theta is 53.1, and the coefficient of kinetic friction is 0.100, I just plugged those values into the equations above...
  34. Lotto

    How many discs will slide off the board as it decelerates?

    I don't undertand the equation. It is Newtons's second law of motion, so it decribes a force that acts on a single disc relative to the ground. So when the force is proportional to velocity, shouldn't it be ##-bv##? Because the dics's velocity is ##v## relative to the ground. Relative to the...
  35. Lotto

    What force is needed to push out this slab on the bottom of the stack?

    The picture is here: I understand that friction I need to overcome is ##5mg\mu##, but why do I need to accelerate the slab on acceleration ##g\mu##?
  36. M

    Box on treadmill connected to a spring

    First i show the sketch of the setup: My first attempt was just to balance out the forces on the box. On the sketch below i have shown the situation where the spring is stretched distance L. In this situation we get the equations: Which when solved leads to All good. I then looked at the...
  37. C

    Finding the time for an object to start rolling without slipping

    For this, I don't understand why they don't have a negative sign as the torque to the friction should be negative. To my understanding, I think the equation 5.27 should be ##I\frac{d \omega}{dt} = -F_{friction}R## from the right hand rule assuming out of the page is positive. Noting that ##f_k...
  38. P

    Filmmaker and inventor fascinated by Physics

    Hi, my question is about electricity, hydrostatic pressure, potential energy and friction. Using an electrically powered compressor (such as compressors used to fill diving bottles) if I fill a tank of volume 10 cubic meters to a pressure of 100psi, 1. what is the potential energy stored in that...
  39. Juanda

    I Solving Wheel Coming to a Stop: FBD, Friction & Hysteresis

    Simple question. Let's say a solid cylinder has an initial speed ##v_o## and it's rotating on infinitely hard ground without air resistance. The cylinder will come to a stop eventually. There are two sources of friction. Since the wheel/cylinder is deformed at the contact patch, there is some...
  40. cutielollipop

    Coefficient of Friction question for a cart going down a wooden ramp

    (mentor note: moved from Classical Physics forum hence no template) Hello, I am having trouble with this question: Imagine in real life there was a coefficient of kinetic friction of 0.4 between the plastic wheels of the cart and the wooden ramp. If there is only friction on the flat part of...
  41. wrobel

    I A pendulum with viscous friction

    Consider the standard pendulum with a weightless rod of length b and a mass point m and mg is applied. In the hinge there is a torque of viscous friction which is proportional ##\omega^2##. Now release the pendulum from the horizontal position. What biggest height does the point m attain after...
  42. Lotto

    B How will object's velocity change when a frictional force increases?

    Let's say that the mass of the objest is suddenly bigger, so when I want to maintain the constant movement, my force must increase as well. But will the velocity have the same magnitude? I think that the velocity will be smaller, so if I want to have the same initial velocity, I must apply an...
  43. Ben2

    Solving Rotary Friction Problem at Ye Olde Swinging Door

    Homework Statement: A door opened at 75 degrees from the latch remains at rest. When moved to a position 60 degrees from the latch, it slowly closes on its own. Is there another possible cause besides a sloping floor? Relevant Equations: \tau = r x F; v = \omega x r; a_T = \alpha x r, where...
  44. al4n

    B Need help understanding some concepts about friction

    We have 2 objects, m1 and m[SUPlB]2[/SUB] Friction is present between the two objects but not between m1 and the floor. A force is exerted on the bottom object which causes it to accelerate parallel to the floor. The thing I'm wondering for while now is, how do I prove that the acceleration of...
  45. jaketodd

    B Things giving rise to static and dynamic coefficients of friction?

    Topography of both the object and the surface. Mass/inertia. Moisture, but that can probably fall under topography. I suppose atmospheric pressure, maybe. Or wind. Magnetism. Any others?
  46. H

    Calculation of Box's Acceleration on a Trailer with Friction

    Question picture: My solution: Where: S is the lineforce Ff is the force as a result of friction a is the resulting acceleration F is the acting force The answear is supposed to be a=(F-2mg(mu))/(m+M) Any idea what i could have missed? Thanks for your help on beforehand!
  47. A

    Why is the work done double its expected value? (conveyer belt)

    The question was this: My calculations show that the answer should be equal to work done on crate to make it reach the same velocity which is equal to 216 J but the answer given is 432 J It is believed that extra energy is needed to overcome friction but friction is an internal force and...
  48. Mohmmad Maaitah

    Shouldn't this be kinetic friction instead of static friction!?

  49. Mohmmad Maaitah

    Minimum stopping distance so a box on a truck doesn't slip (friction)

  50. Argonaut

    Work-Energy Theorem and Friction

    My final answer is different from the official one in the back of the book, and I can't figure out what I did wrong. This is my attempt: Let block 1 be the vertically moving block and let block 2 be the horizontally moving one. Also, let ##m_1 = 6.00 ~\rm{kg}##, ##m_2 = 8.00 ~\rm{kg}##, ##v_0...
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