What is Frictional force: Definition and 260 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. chwala

    Find the value of ##θ## and frictional force acting on the block.

    Refreshing on this...This is a relatively new area to me ...my solutions should be correct...what i am trying to engage on is if there are any other ways of looking at the same problem. Ok in my working i have, ##30 + 35 \cos β-45=0## ##\cos β=0.4286## ##β = 64.62^0, ⇒θ=25.4^0 ## to one...
  2. E

    I A Continuous Solution for Mass/Spring w/ Friction

    Suppose we have mass ##m## attached to spring with constant ##k##, and some coefficient of kinetic friction ##\mu## between the mass and the surface. Its displaced from equilibrium by some distance ##x## at ## t = 0 ##. I've come up with the following ODE to described ##x(t)## using the...
  3. A

    How to Solve for Delta_h: A Math Question

    b) My question is here! 0.9v_t = v0 + a*t = a*t t = 0.9v_t/a delta_h = v0*t + 0.5*a*t^2 = 0.5*a*t^2 = 0.5*((0.9*v_t)^2)/a = where a = (-m*g + b*v)/m delta_h = (0.5*((0.9*v_t)^2)*m)/(-m*g + b*v) plugging in everything delta_h = 1.65 m which is not what the answer is. Please help
  4. vibha_ganji

    B What Happens When The Applied Force Equals the Static Friction Force?

    In my teacher’s notes, it said that when the applied force on an object equals the maximum static frictional force, the object begins to move at constant velocity. My question is if both the applied force and the frictional force cancel as they are equal in magnitude, what force accelerates the...
  5. imbadatphysics212

    Writing an expression for work done by frictional force

    I took a stab at the question, but I don't think I did it right. I know that Work = Change in Energy thus, Work = final energy - initial energy Because there is no energy at the final position, then final energy = 0 (I'm not sure if this is correct). So I got the equation W = 0 - (1/2kA^2 +...
  6. Kaushik

    Find the frictional force acting on a solid cylinder

    This was the answer key provided: My questions are the following: if the force required for rotational equilibrium is more than the limiting static friction, then the body will rotate aka slip over the surface. When it slips, the frictional force will be kinetic and not static, right? If I...
  7. H

    The magnitudes of the applied force F and the frictional force f of a wheel

    I calculate in this way as follows and get a correct answer. Howere I am not sure if I am using the right way. F R = (½ MR^2 + MR^2 ) a/R F = 3/2 Ma F - f = Ma f = 3/2 Ma - Ma = Ma/2
  8. S

    What is the maximum frictional force?

    In the attachment I am supposed to calculate the maximum frictional force of a block on a 35 degree angle incline (that is the point at which the force acting opposite frictional force is highest) I make it out to be sin(35)*120N = 69N but the book says 675N and it gives it as...
  9. G

    Determining the power of frictional force

    I can say that the frictional force always against the rolling sphere and the velocity is increasing for the ball. So The dot product F.v keeps on getting more and more negative, so how can the Pf remain constant? Well the velocity increases along the incline and the force of gravity is down...
  10. 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...
  11. J

    What is the frictional force on a wheel-disk system?

    The figure is in the attached image. My attempt: I(wheel-disk system) = 0.5mr^2 + MR ^2 = 0.5(0.2kg)(0.1m)^2 + (1.5kg)(0.3m)^2 = 0.136(kg)(m^2) Fnet(of object) = Ma Mg - T = Ma T = Mg - Ma Fnet (wheel-disk system) = (M+m)a Mg- Ma - Fr = (M+m)a a = 0 because system in equilibrium Mg -...
  12. Lightning0145

    What exactly is limiting frictional force?

    Given that a body is moving with a constant velocity on a rough surface. Is it possible to say that if the force (which keeps the body moving with a constant velocity) is withdrawn then the rate at which it will decelerate = limiting frictional force / mass of the body? {Force = m * a}. Thank you.
  13. Benjamin_harsh

    Difference between frictional force and the force of friction

    Problem Statement: Difference between frictional force and force of friction. Relevant Equations: Difference between frictional force and force of friction. Difference between frictional force and force of friction. Are these two terms equal?
  14. Dayal Kumar

    Frictional force between two rotating cylinders

    Homework Statement .A cylinder P of radius rP is being rotated at a constant angular velocity ωP along positive y-axis with the help of a motor about its axis that is fixed. Another cylinder Q of radius rQ free to rotate about its axis that is also fixed is touched with and pressed on P making...
  15. K

    Calculating the frictional forces on a sliding box on a ramp

    Homework Statement We kick a box upwards a ramp. The box slides upwards, then slides backwards again. We ignore the air drag and other factors. We only look at the gravity, normal forces and friction forces. Forces on the box when it's moving upwards: Weight of the box is 0.123 KGs. Angle...
  16. isukatphysics69

    Find the frictional force between a block and a wall

    1. Homework Statement A block weighing 22 N is pushed against a vertical wall by a force of magnitude 60 N directed 30° above the horizontal. The block is intitally at rest. The coefficient of static friction between the wall and the block is 0.55 and the coefficient of kinetic friction between...
  17. E

    Displacement of an object with certain Ek stopped by Frictional Force

    Please do excuse if certain terms are not the most technical ones as I am translating the problem from another language. Do feel free to kindly inform me of the more technical term that substitues the sloppy one I've used. (And do excuse the generally bad English overall :-)) 1. Homework...
  18. lichenguy

    Conceptual question about frictional force and equilibrium

    A uniform beam of length L and mass m is inclined at an angle θ to the horizontal. Its upper end is connected to a wall by a rope, and its lower end rests on a rough, horizontal surface. The coefficient of static friction between the beam and surface is μs. Assume that the angle θ is such that...
  19. A

    Calculating the Static Frictional Force of Nylon Bushings

    Hi guys I'm looking to calculate the static frictional force for a hinge Below is a CAD image of the component I am testing. I am thinking of attaching a hook onto the plate as shown below, and continuously add weights at the end of the hook until the hinge begins to move. By multiplying...
  20. Rotnort

    Magnitude of Frictional Force in Simple Harmonic Motion

    Homework Statement I do not fully grasp the concept behind all of these sub questions (i)-(iv). Homework Equations v=wAcos(wt) (SMH)? Friction Force = Coefficient of Friction * Normal Force The Attempt at a Solution (i) Varying as simple harmonic motion sees varying acceleration as it...
  21. MagdaStan

    Acceleration of the object, distance, kinematic coefficient

    Hello guys. i know i shouldn't be doing this, but I am asking you if you can help me with a problem for my younger sister, because my major is something else (biology, genetics) and she need this and doesn't know how to solve it.. 1. Homework Statement At an upper end of the slope inclined at...
  22. AilingLore21

    Negative Values of the Frictional Force?

    Homework Statement Ignore B & C for now The block in the figure reaches a velocity of 40 m/sec in 100 m, starting from rest. Compute the coefficient of kinetic friction between the block and the ground. W = 100N F = 40 N 2. Homework Equations ∑Fy = 0 so Normal Force = Weight ∑Fx =...
  23. J

    Determine the frictional force

    Homework Statement If a 2.5 kg rubber ball is rolled across the dry concrete with an acceleration of 4.0 m/s^2[E]. Determine the friction force required to stop the ball. Homework Equations [/B] Coefficient of kinetic force between rubber and dry concrete is 1.0, Fnet = (m)(a) Ff= (u)(Fn)...
  24. S

    Calculate the Kinetic Frictional Force

    The alarm at a fire station rings and a 71.3-kg fireman, starting from rest, slides down a pole to the floor below (a distance of 3.63 m). Just before landing, his speed is 1.42 m/s. What is the magnitude of the kinetic frictional force exerted on the fireman as he slides down the pole? Givens...
  25. A

    Car Crash Work and Energy Problem

    Homework Statement A red van came through and crashed into a green van. The driver of the red van claims that he was driving at a speed of 11 meters/second at the moment of the crash. You want to find out if his claim is true. a. the mass of the red van is 1000 kg b. the mass of the green van...
  26. R

    Finding Frictional Force and Power Using Work and Energy

    Homework Statement To measure the combined force of friction (rolling friction plus air drag) on a moving car, an automotive engineering team you are on turns off the engine and allows the car to coast down hills of known steepness. The team collects the following data: (1) On a 2.70° hill, the...
  27. J

    Frictional Force Problem: Solve with 25kg & 0.36 Coefficient

    The problem seems very straight forward, however it's proving stubborn. The problem is as follows: We have a mass of 25kg sliding on a table with a frictional coefficient of 0.36. What is the frictional force in Newtons? Now, I know the force of friction to be Fƒ = μmg and also Fƒ = μmg⋅cosα...
  28. T

    Frictional force and surface area in contact

    I've read that the surface area of an object in contact with the ground doesn't not affect the frictional force acting on it as it is pushed forward. I kinda understand what is explained but I find it difficult to reconcile with what happens in real life... Don't wheels reduce the surface...
  29. S

    Calculating Distance: Free Body Diagram for Box Sliding with Friction

    Homework Statement A 250 kg box slides down the ramp and then across a level floor. The coefficient of kinetic friction along the floor is 0.20. A person see the box moving at 1.0 m/s(left) and pushes on it with a horizontal force of 140 N (right). How far does the box travel before coming to...
  30. EmilyBergendahl

    Work and the Frictional Force (Grade 12 Physics)

    Homework Statement A boy does 465 J of work pulling an empty wagon along level ground with a force of 111 N [31° below the horizontal]. A frictional force of 155 N opposes the motion and is actually slowing the wagon down from an initial high velocity. The distance the wagon travels is _____...
  31. P

    Magnitude and Direction of Frictional Force on a Moving Object

    Homework Statement You pull on a 30 kg box with a horizontal force of 110 N to the right. (i) If there are no other forces acting on this box, what is the resulting acceleration? (ii) If the resulting acceleration of the block is only 1.6 m/s, what is the magnitude and direction of the...
  32. K

    How Much Friction is Needed to Keep the Ladder in Place?

    Homework Statement A 5.00-m long uniform ladder leans against a smooth wall and its base rests on a rough floor. The ladder has a mass of 18.0 kg and its base is a distance of 2.30 m from the wall. A person of mass 70.0 kg climbs 2.50 m up the ladder. If the ladder is to remain in place, what...
  33. B

    Direction of Frictional Force in Relation to Net Non-Friction Forces

    Homework Statement This is not a specific problem, but is it true that if you added all of the forces acting on an object except for friction, that the direction of friction would be opposite the direction of that net force(technically, it's the net force except friction)? For example, If you...
  34. B

    Find stopping distance from mass velocity & frictional force

    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown > A 50,000kg locomotive is traveling at 10m/s on a level track when the engines and brakes both fail. If there is a frictional force of 142N acting to slow it down, how far will it roll before it...
  35. J

    Frictional force on an inclined plane

    Homework Statement A suitcase of mass 16 kg is placed on a ramp inclined at 15 ° to the horizontal. The coefficient of friction between the suitcase and the ramp is 0.4. Determine whether the suitcase rests in equilibrium on the ramp, and state the magnitude of the frictional force acting on...
  36. Priyadarshini

    What is the Frictional Force Acting on a Block on a Rough Incline Plane?

    Homework Statement A block of mass 10kg is released on a rough incline plane which is inclined at 30 degrees. Block start descending with acceleretion 2m/s^2. Kinetic friction force acting on the block is: A) 10. B) 30. C) 50. D) 50*3^(1/2) Homework Equations f= meu*N a=meu*g The Attempt at a...
  37. Priyadarshini

    Value of frictional force applied

    Homework Statement The mass of A is 5kg and the mass of B is 10kg. If the acceleration of A is 2m/s^2 which is smaller than acceleration of B, where A is placed on top of B, then the value of frictional force applied by B on A is: A) 50N. B) 20N. C) 10N. D) None of these Homework Equations...
  38. C

    Block on an incline and frictional force

    Homework Statement A 4.00-kg block rests on a 30.0 degree incline. If the coefficient of static friction between the block and the incline is 0.700, with what magnitude force must a horizontal force act on the block to start it moving up the incline? Homework Equations F=ma...
  39. K

    Find the frictional force on the block

    Homework Statement When an 8.0 N force is exerted horizontally on a 10.0 kg block, the block’s acceleration across a level surface is 0.2 m/s2. a. Find the coefficient of kinetic friction between the block and the surface. b. Find the frictional force on the block. c. Find the net...
  40. P

    Box Pulled on Rough Horizontal Surface - Frictional Force

    Homework Statement A 100N box is initially at rest on a rough horizontal surface. The coefficient of static friction between the box and the surface is 0.6 and the coefficient of kinetic friction is 0.4. A constant 35N force is aplied to the box horizontally. Identify from choices (a) - (e)...
  41. D

    Is mgsinθ=static frictional force on an inclined plane?

    According to Newton's 3rd law, for every force there's an equal opposing force. Since a block is sitting on an inclined plane, wouldn't that mean the static friction is acting like the opposing force for mgsinθ thus, mgsinθ=static frictional force? Please respond
  42. T

    What are the equal-and-opposite forces of friction forces?

    Homework Statement A block rests on a table, and a second block, connected to the first with a rope, hangs over the side of the table. See the illustration. (Assume the pulley is massless and frictionless.) All objects pictured are stationary. Identify every force involved in the pictured...
  43. M

    Theoretical frictional force of a mass going down a ramp

    Homework Statement So, we did a lab wherein we rolled a 1.001kg cart down a 24.4 degree slope. We used a ticker tape timer and are trying to find the frictional force of the ticker tape timer alone. The problem is, I can't figure out how to find the acceleration for the equation Homework...
  44. E

    Rotational motion, find the frictional force.

    Homework Statement A small 350-g collar C can slide on a semicircular rod which is made to rotate about the vertical AB at a constant rate of 7.5 rad/s. The coefficients of friction are μs = 0.25 and μk = 0.20. Homework Equations Tangent Velocity= Radians*radius Normal acceleration an=...
  45. Rococo

    Frictional force acting between 2 stacked blocks

    Homework Statement [/B] In the figure above, block A has mass ##m_A=25kg## and block B has mass ##m_B=10kg##. Both blocks move with constant acceleration ##a=2m/s^2## to the right, and the coefficient of static friction between the two blocks is ##\mu_s = 0.8##. The static frictional force...
  46. A

    Frictional Force on ball rolling down incline

    Hi everyone, For an experiment I wanted to investigate the forces acting on a ball when rolling down an incline. Basically I have a wooden incline with a photogate at the bottom to measure the velocity of the ball at the bottom of the ramp. At the top of ramp the sphere has potential energy...
  47. D

    Frictional Force vs normal force

    Homework Statement A 10 N horizontal force is applied to a 50 N block initially at rest on a rough horizontal surface. If the coefficient of static friction is 0.5 and the coefficient of kinetic friction is 0.4, then the frictional force on the block is A 10 N B 20 N C 0 N D...
  48. R

    Calculating frictional force given mass and coefficient?

    The mass of a steel block is 760.9 g, the static coefficient of friction is 0.15, how do i find the frictional force in Newtons?
  49. S

    Direction of frictional force when running

    When a person is running is frictional force forward or backward? I do not have good knowledge of