What is Friction coefficient: Definition and 122 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. daraphy

    B Coefficient of friction in sea water

    Is there any friction coefficient in the sea as there is in ground? I've tried searching but I see results between 0.4 and 25.7 (?). If there's no such thing as a coefficient of friction to water, how do I calculate the amount of force to start moving a X mass object in water?
  2. latos

    Coefficient of kinetic friction of a block sliding across the ceiling

    I first found the force of friction by setting the force in the x direction (horizontal component of force applied - friction) = ma. I then thought the normal force would be equal to vertical component of the force applied because of Newton's 3rd Law, which states that for every action, there is...
  3. I

    Why do I keep getting friction coefficient as a negative?

    I mean, I know why I am getting that result(because acceleration is negative), and I know that is wrong butI don't understand how do I get the correct answer... m=5000kg Vi=10m/s -> initial velocity Vf=0 -> final velocity t=5s mi=?I first calculated acceleration(Vf=Vi+at -> a=-10/5= -2m/s^2...
  4. qnach

    I Stribeck v.s. Coulomb friction law

    The friction law I learnt in high-school is Coulomb law, to my understanding. But what is Stribeck law? What is the difference from Coulomb's law?
  5. C

    How to find coefficient of friction of a body sliding down the slope?

    So basically I need to find the coefficient of friction given the listed information. What bothers me is that I am getting two different accelerations for two different approaches. When I calculate acceleration using Fg=mgsin60 I do it this way: Fg=mgsin60 -> ma=mgsin60 ->a=gsin60 -> a=8.66. But...
  6. H

    Finding the work done by a block

    We want to figure out how much work friction does on a block as it slides down an inclined plane with a rough surface. we find the force due to gravity that pulls the block down the ramp, that's found by M * g * sin(θ), The normal force on the block is given by M * g * cos(θ). The force of...
  7. BurpHa

    Static Friction Between a Box and the Floor

    I don't understand part (b) In part (a), I need to calculate the coefficient of the static friction: mg * \mu_static = 35 58.8 * \mu_static = 35 \mu_static = 35 / 58.8 \approx 0.6 So from part (a) I know that the force applied is equal to the static friction, meaning that the box cannot...
  8. S

    Distance travelled by a car considering only air friction?

    TL;DR Summary: Distance traveled by a car considering only air friction? How much distance would a 3-ton car travel if its initial speed was 17 km/h and we only take into account air's friction? (Assume that the car has an airfoil-like shape, so that the resistance against the air is very low)...
  9. T

    I What is the difference between the resistance force and the friction coefficient?

    Hi I have been wondering what is the difference between resistance force and friction coefficient. While doing research online I could not find a clear answer. Maybe someone here will now:bow:
  10. E

    Yes! Calculating Friction Coefficient

    Fg = m * g: Fg = 30 * 9.8 = 294 N Fnet = m * a: Fnet = 30 * 1.2 = 36 N Fax = Fnet + Ff: Fax = 36 + 10 = 46 Fa = Fax / cos(angle): Fa = 46 / cos(25) = 50.75 Fay = Fa * sin(angle): Fay = 50.76 * sin(25) = 21.45 Fn = Fg - Fay: Fn = 294 - 21.45 = 272.55 Ff = mu kinetic * Fn, solving for...
  11. S

    Problem of spring block system: force vs conservation of energy

    I have used the work energy theorem like all source have shown me an have arrived at the right answer where work one by all the forces is the change in kinetic energy -1/2kx^2 - umgcosΘx +mgsinΘx = 0 is the equation which becomes -1/2kx -umgcosΘ+ mgsinΘ = 0 where k= spring constant u=...
  12. G

    A piece slides down a slippery plane plane slowing from 10 km/h to 5km/h -- what is the friction coefficient?

    I don't know how solve this.. [User has been reminded by the Mentors to show their work on schoolwork problems]
  13. TheBigDig

    Forces acting on a car on an incline

    For part 1, I got ## tan \alpha = 1/30 ## ##\alpha = 1.9^{\circ}## ##mgcos(1.9) = 10774N## I'm a little thrown off by the second part. Are we supposed to assume that in the absence of friction, F = N and then substitute F = ma to solve for this?
  14. xWaldorf

    I Friction Coefficient of Marble & Iron on Plastic

    hey, i was looking for information on friction coefficient of marble on plastic and iron on plastic. if you know these values i'll be very glad! thanks in advance
  15. P

    Static friction coefficient for a crate in the back of a truck

    I drew a free body diagram for the crate. I have normal force going up, weight down, static friction force to the left and the force of the crate sliding to the right. I'm assuming the truck is moving to the left. I have Fnet=0 because the crate is not moving, so the forces are balanced. I...
  16. FEAnalyst

    Friction - problem with one of the equilibrium equations

    Hi, actually it's not my homework, I'm just practicing some academic problems after a long break but it seems that I should post this here anyway. Here's a scheme of the problem that I want to solve: The task is to calculate minimum force ##P## for the system to stay in equilibrium. And...
  17. Hamiltonian

    Two block problems with friction

    the maximum value of friction between the surfaces of the blocks is ##60N## the friction should be self-adjusting until this maximum value. Hence the force of friction in the given scenario should be = 30N but this is physically impossible as if this is the case the top block will be at rest and...
  18. Hamiltonian

    Why Does the Friction Force Not Match in the Two Block Problem?

    when a force of 10N is applied to the 4kg block the force of friction between the two blocks will also equal 10N as the maximum value of friction between the two surfaces is f = N##\mu## = 20N. if you look at this free body diagram f = F = 10N so the net force acting on the top(4kg) block will...
  19. U

    Why is rolling easier than sliding?

    I learned that rolling involves the coefficient of static friction unlike sliding that involves the coefficient of kinetic friction. It's known that the coefficient of static friction is always higher than the coefficient of kinetic friction. This should result in rolling to be more difficult...
  20. Thijske

    Kinetic friction coefficient of aluminum on lubricated cast iron

    Hey all, I was recently searching for kinetic friction coefficients, and I noticed that for a reason which is unknown to me, some materials had not been appointed such coefficient. The specific kinetic friction coefficient that I'm looking for is aluminum on greasy/lubricated cast iron. Any type...
  21. Huger

    Friction coefficient and the force on a syringe plunger

    I need to conduct an experiment and measure how what is the coefficient and force of friction of the rubber that pushes down along the edge inside the syringe. The thing is I can’t use a dynamometer.
  22. Addez123

    Find the kinetic friction coefficient

    Image1, the exercise. My solution: Image2, my solution The answer is .37 but I keep getting .45 What am I doing wrong?
  23. M

    Need to calculate the friction coefficient

    Homework Statement Hello. I have slope = 45 degrees, at distance 36.4cm (0.364m) object gains 2m/s speed. Need to calculate friction coefficient. Correct answer is ( 0,2). How to calculate? Homework Equations 1) t = s/v "t" - time; "s" - distance "v" - speed 2) S =...
  24. milo_ec

    Misc. Maximizing Friction Coefficient for Mini-Sumo Robot Tires: Tips and Tricks

    Hi, I was recently tasked to build a mini-sumo robot (10x10cm. 500g. the objective is to push your opponent out of a 75cm. diameter arena or dohyo), and I was wondering about the tires that I'm going to use. I want to increase the friction coefficient as much as I can, so I was wondering how to...
  25. M

    Inclined Plane Static Friction Coefficient

    Homework Statement The static friction coefficient on an inclined plane is equal to tan(θ). The problem requires me to prove this also works by using an x-axis parallel to the ground rather than parallel to the incline. I understand how to get tan(θ) using the incline as the x-axis, but I don't...
  26. T

    Two moving objects - box and cart

    Homework Statement We have a cart (It is very long) and a box on it.They are at first stationary but at ##t=0##, cart begins to move with ##v## such that: ##v = \alpha t^\beta ; t\leq t_0## and ##\dot v = c; t>t_0 ## where ##\alpha ,\beta ,c## are constants. At the time ##t1 (t_1<t_0)## the...
  27. devilish_wit

    A question about contact forces and friction

    Homework Statement Two blocks of masses m1 and m2 are placed on a table in contact with each other as shown in the figure below. The coefficient of kinetic friction between the block of mass m1 and the table is μ1, and that between the block of mass m2 and the table is μ2. A horizontal force of...
  28. P

    Can the max friction be determined in B-ii?

    This question is on our worksheet for this week. Part A and B-i I'm fine with. Part B-ii I'm confused by. I've asked my physics lecturer and he implied there is a way of finding fs,max using part B-i. My class tutor was a bit confused by the wording of the question and tried to break part of...
  29. N

    What is the coefficient of friction in this inclined plane problem?

    Homework Statement Two bodies with mass m1 and m2 are tied together with an inexstensible and massless string rolled over a massless pulley put at the top of the incline with angle 30 . m2=5 kg which is on the incline is blocked and T=10 N . m2 is let loose and the system starts moving freely...
  30. Mafalda

    Finding the direction of the force knowing the mu static

    1. A crate resting on a rough horizontal floor is to be moved horizontally. The coefficient of static friction is 0.40. To start the crate moving with the least possible applied force, in what direction should the force be applied? a. Horizontal b. 24 degrees below horizontal c. 22 degrees...
  31. S

    Calculating Friction Force for a Waterproof Seal in a Syringe Setup

    Hi Friends, So I'll go into a bit of the setup that I'm having some trouble figuring out. I have a piece of rubber that will be pushing up against the side of a metal (or plastic) container to create a waterproof seal. The easiest way to think about this would be to imagine the rubber piece of...
  32. JHLee

    Calculating Tension Using Work Energy Theorem

    Hi, I have a homework and I kind of stuck on it. Here is the question: A 17 kg object on a rough ramp (coefficient of friction = 0.35N, ramp's angle = 25 degrees) is connected to a vertically hanging object via a pulley with I = 23 kg m^2 and the radius is 0.25m. The hanging object had weight...
  33. J

    How do I calculate the mass of a moving object?

    Homework Statement Someone mistakenly threw away a lovely couch, and you decide to take it back to your apartment. You push it with a force of 350 Newtons and at 30 degrees below the horizontal at 2 m/s. The coefficents of friction are μs = 0.4 and μf = 0.3. What is the couch's mass? Homework...
  34. K

    Calculating Kinetic Friction Coefficient for Sliding Soccer Player

    [note from mentor: this was originally posted in a non-homework forum, so it lacks the homework template.] Hi guys, I need your help with the last part of following problem please. A soccer player with 70kg mass slides for 0.75 seconds on the grass to stop a soccer ball. 1) Acceleration...
  35. T

    Find friction coefficient given initial and final velocity

    I am not sure how to approach a problem involving the friction coefficient when only given initial velocity, final velocity, and distance traveled. I could combine the friction and kinematic equations, but I am only familiar with doing that for one velocity... Here is the specific problem I had...
  36. B

    Friction Problem of a Crate Sliding Down a Ramp

    Homework Statement A steel washer is suspended inside an empty shipping crate from a light string attached to the top of the crate. The crate slides down a long ramp that is inclined at an angle of 38 ∘ above the horizontal. The crate has mass 239 kg . You are sitting inside the crate (with a...
  37. EEristavi

    Automotive Friction force, Coefficient of friction &Traction

    I have few (more or less) general questions: 1. I know that: "The coefficients of friction are nearly independent of the area of contact between the surfaces". I understand this, but I know from everyday life, when car tire tread is worn off, braking distance increases and maximum acceleration...
  38. C

    Car acceleration on concrete and on asphalt

    Today I've come across the statement that the coefficient of static friction of rubber tires on asphalt is bigger than that of tires on concrete. Does it mean that the maximal acceleration a car can attain on asphalt will be greater than that on concrete? My assumptions: 1)The force of friction...
  39. S

    A block of mass m=0.2 kg, is pushed by a spring of stiffness k=300 N/m

    I am currently taking a physics class and I'm studying for the final and I've been stuck on this problem and haven't been able to find help from the book nor help from online. The professor said the answer was .56m, but I've been trying formulas for about an hour now and haven't been getting...
  40. P

    Turbulent friction coefficient over a plate

    Homework Statement Homework Equations Cf=0.0577(μ/xρUm)0.2 The Attempt at a Solution I've managed to do parts a) and b), however I don't believe my attempt at the first part is correct as I am using a different Cf than the value used in the mark scheme. The expression I made for the first...
  41. tensor0910

    Solve for friction coefficient of block on sp

    1. Homework Statement A block of mass 1.60 kg is connected to a spring of spring constant 152 N/m which is then set into oscillation on a surface with a small coefficient of kinetic friction. The mass is pulled back 34.6 cm to the right and released. On the first right to left oscillation...
  42. RoboNerd

    Question about finding static friction coefficient

    Homework Statement Two boxes each weighing 900 N are stacked on a horizontal floor. Box A is on the bottom, box B is on the top. The coefficient of static friction between box a and the floor is 0.3. A worker applies a force of 600 N to box b parallel to the floor, and the stack moves together...
  43. R

    Tank tracks treads friction coefficient

    What kind and value is the friction coefficient of tank tracks on the move, when force is applied forward in the direction of the tracks movement? Is the friction coefficient in that case, closer to kinetic/sliding coefficient or to a rolling resistance coefficient? What about the sideways...
  44. F

    Calculate acceleration and kinetic friction coefficient

    Homework Statement A particle of mass M is released from rest on a rough inclined plane, which makes an angle of 30° with the horizontal. It is observed that the particle moves a distance of 3 m in 3 s. What is the particle’s acceleration? Draw a properly labelled free body diagram. Calculate...
  45. B

    Finding friction coefficient, car unbanked curve.

    Homework Statement What is the minimum coefficient of friction needed between the tires and the ground so you make the turn safely?[/B] Car= 1394.7kg You=75kg Radius of turn = 40m Velocity = 20m/s Homework Equations Fnet = MAc (Ac = centripetal Acceleration) = Force of friction Force of...
  46. S

    Power Transmission with Friction Coefficient: 0.25 to 0.2

    1. Homework Statement After a certain amount of running, there is likely to be changes in the values of the engineering parameters of the system in section (a). One of these is the friction coefficient, Carry out the activity with calculations to find out the effect on power transmission if...
  47. K

    What is the kinetic friction coefficient?

    Homework Statement A skier is sliding down a 20o slope at constant speed, what is the kinetic friction coefficient? Homework Equations E = 1/2 mv2 W = Fd F = ma F = μN = μmg The Attempt at a Solution Attempted to use ma = μmgsin20, which crosses out the masses since mass was not given, but...