Friction Definition and 435 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. James Brown

    B How come friction can make a car turn?

    How is it possible that friction makes car turn? From what I know, frictional force is acting along to the direction of the wheel turns. When the car turns, the direction of the frictional force now act opposite to the direction of the wheel turns! I'm sure if you rotate the steering wheel to...
    • James Brown
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    • Accelerate Centripetal force Friction
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  2. F

    Horizontal impulse on a ball at rest on a plane (with friction)

    Summary:: I'd like to check my understanding of standard problems where a billiard ball resting on a plane is hit horizontally at some height above its center So the situation is that a ball of mass ##m## and radius ##r## is at rest on a horizontal surface. There is friction between the ball...
  3. A

    I Net internal torque = 0

    In a system, the net internal torque should be 0. If we have two fly wheels, one spinning with angular velocity w, and the other at rest and the flywheel at rest is dropped onto the other flywheel, the two fly wheels reach the same angular velocity due to friction between the two wheels. I am...
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  4. J

    I Direction of friction of each wheel and total moment when a car turns

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    • JM7
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    • Centripetal force Friction Newtonian mechanics Uniform circular motion
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  5. L

    How long would a lever have to be to compete with a hydroelectric dam?

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  6. A

    Finding kinetic energy and initial velocity of a cart over time

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  7. L

    A sphere rolling without slipping down a hemisphere

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  8. SpectraPhy09

    Plotting the graph of Friction Force vs. time (Laws of motion)

    F.B.D Of first block (I have shown only the horizontal Forces) f1(max) = μ (1kg)(g) = 0.5 * 10 = 5N F.B.D Of the second Block f2(max) = μ (3kg)(g) = 15N Now the string will become taut and the tension will start acting when f = t = 5N But for 0<f<5N there will be no motion between the 1 kg...
  9. P

    The velocity of a movable block that is penetrated by an arrow

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  10. J

    Equation calculations about the coefficient of kinetic friction

    I need an expert to verify equations about the coefficient of kinetic friction.
  11. 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?
  12. L

    Is there any friction in this case?

    In the experiment, a cart on an inclined plane of 30 degrees is hooked with the force metre by a line. The line is tension T. It is also subjected to the force of gravity Fg. This makes the cart in static equilibrium. But since the cart is hooked with a line, it does not slide down. The net...
  13. T

    A Cylinder Rolling in a V-Groove

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  14. T

    Circular motion of a mass on a string on an inclined plane

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  15. T

    Stopping a Bullet

    (a) ##u_{min}=\big(1+\frac{m_2}{m_1}\big)\sqrt{2\mu_k g d}## (b) ##x_f=\sqrt{\frac{2h}{g}\Big(\big(\frac{m_1}{m_1+m_2}u\big)^2-2\mu_k g d\Big)}## Can someone check please?
  16. V

    Reason for glass rod losing electrons

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  17. C

    Capstan equation, Euler's formula, power law friction

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  18. F

    A ball climbing a ramp while "rolling the wrong way"

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  19. FEAnalyst

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    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...
  20. Kaushik

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    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...
  21. schrodingerwitch

    Vectorial issue of friction

    Considering an stopped object in a horizontal plane, the frictional force between the object and the plane would be the product of the friction coefficient (static or kinetic if there was movement between the surfaces) by normal. Since the normal in this case would be given by N (vector) = - mg...
  22. J

    Applications of Newton's laws - coefficient of friction

  23. SamRoss

    B Simple forces described in terms of fundamental forces

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  24. 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...
  25. goodOrBad

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  26. goodOrBad

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  27. goodOrBad

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  28. C

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    Look on picture two for my equations, I’m pretty sure my first three equations are correct as it’s the same on the answer paper I got. Answer paper only shows the three equations and correct answer so I have no idea how they got to it. When I put the equations togheter And solve out ”h” i get...
  29. Hamiltonian

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  30. Like Tony Stark

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  31. Hamiltonian

    Two blocks kept side by side and friction between them

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  32. M

    How do I read this equation for air friction/drag on an object?

    I am trying to understand an excerpt from an article describing the vibrations of a string (eg. guitar/piano) which reads as follows: This is basically the wave equation with Δm representing a small piece of mass from an interval of the string and two forces added to the right side. He...
    • mikejm
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  33. ItsukaKitto

    Maximum height a block reaches after separating from a curved moving ramp

    Diagram attached at the end I personally think there's something wrong with this question, and I'd like if someone can tell me whether it's the question that is wrong or my approach. If I attempt the solution thinking that M should be stationary, the solution is simple. 0 - 1/2 mv^2 = -mgh...
  34. Rahulx084

    Some questions about Friction in fluid flow

    I have few conceptual doubts in fluid mechanics. Here is the one I will ask first. I want to understand the force direction acting on the solid liq interface during fluid flow, Lets say a fluid is flowing in a pipe. Now the fluid applies a shear stress at the walls of pipe in the direction of...
  35. rakailee

    Truck with attached inclined plane and a block on the incline

    I tried solving this by assuming the acceleration of the truck and block to be the same so the block would stay on the incline. Also, I would assume truck ma = static friction, block ma = mgsintheta... then I solved for a to plug into 1st equation to get 12990 N. Is this correct? I wasn't sure...
  36. 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...
  37. Physics lover

    Value of frictional forces in a 3-block system

    So I started by checking the options.I substituted the value of friction in the equations I got by making free body diagrams.I got different value of Tensions.For 1 and 3 Tension came to be 38 N.For 2 Tension came out to be 42N and for 4 Tension came out to be 40 N. Now I think that I will take...
  38. J

    What is the orientation of the vector of friction?

    Hi, It is my first message :) I hope you are all fine and safe in these difficult days ! I cannot find the good orientation of the vector of friction. A circle moves in translation to the right and in the same time the wall rotates around A0. A0 is fixed to the ground. There is always the...
    • JrK
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  39. SilverSoldier

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    Basically, I want to know if my assumptions and workings are correct. This is how I see this situation. First, I'm viewing this body as a series of disconnected points, like I have in this animation I made, modeling purely rolling motion. Modeling the body like that worked in that case, and...
  40. K

    Aerodynamics of a Train

    Summary:: How can I measure the friction of a train with its rails and the air. How can I measure the friction of a train with its rails and the air. You can assume that the face of the train is like the picture below. If you need any specifications just let me know
  41. rakailee

    Box on a slanted plank with friction attached to a spring

    I first find the force of friction to be (2)(9.8)cos(65)(.22), then I find the pull of gravity to be (2)(9.8)sin(65). The full equation I set up to be: 0 = kx + force of friction minus the pull of gravity This gives me the wrong answer, 0.44 . My free-body diagram is that kx and force of...
  42. MathDestructor

    Mechanics: Slope Friction Problem

    So far, I have this: For Part ii) I know that: mgh = xmgsin(theta), but I don't know how to go further
  43. Kaushik

    Friction and surface area

    From what I read on the internet I found that increase in surface area that is in contact is offset by the reduction in pressure. What exactly does it mean? This is what I understood from the it (but my understanding might be absurd :-p): does reduction in pressure mean that the "hills" or...
  44. Helena Durrant

    Problem involving friction, with a mass being pulled up a slope

    (The answer from the markscheme is 26.7)
  45. 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...
    • Thijske
    • Thread
    • friction friction coefficient frictional force kinetic friction kinetic frictional force
    • Replies: 2
    • Forum: Mechanical Engineering
  46. T

    AP Physics 1 Help? Centripetal motion/Kinematics/Friction problem

    I think I have solved the first three, and only really need help on question four. For number one, I used Fc = (Mv^2)/R and just rearranged it for velocity so I ended up with v = sqrt(ac * R) For number 2 I used Ff = Fn*mu and got Mg*mu = Ff For number 3 I used w = Ff*d and got w = -Mg*mu*l...
  47. K

    B Resistive force that a nail will have to overcome to penetrate a piece of wood

    lets say a hammer of 0.5kg strikes a nail at 10m/s. The nail penetrates into the wood by 1cm. The reason why the nail stops is because friction has eventually overcome the nails momentum. The retardation of the nail can be worked out, but Can you calculate the force that stops the nail if you...
  48. Prabs3257

    Velocity of an object on an inclined plane

    I used work energy theorem between initial top point and point x along the incline(downwards) i got the expression of v then diffrentiated it to get a maxima but it gives me a wrong ans which is 10/6 but the actual ans is 10/3 please tell me what i did wrong
  49. K

    Multi-surface Frictional force

  50. Alfreds9

    Saw characteristics influencing efficiency in sawing steel?

    Hello, I am having a headache to try understand a possibly simple real-world problem: efficiency (as in number of strokes/cumulative length needed) to saw steel, assuming a constant sawing length per stroke and a known steel sectional area. I began to think about the few assumptions I assume...
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