What is Friction factor: Definition and 24 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. 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...
  2. J

    Uncertainty - Reynolds number and the friction factor

    Homework Statement Correctly present the table of information. The values in the table are deliberately in a wrong format. The calculated Re values have been analysed to have an uncertainty of ± 0.4% and the calculated f values an uncertainty of ± 0.1%. Homework EquationsThe Attempt at a...
  3. R

    Dow Molykote 3402C: What is the Friction Factor (K)?

    OK guys/gals, question of the century: What is the friction factor (K) for Dow's Molykote 3402C anti-friction coating? thanks for any insight...
  4. M

    Need help with a specific (slope) problem in dynamics

    Homework Statement An object is placed on a slope with initial velocity v=0m/s. Angle of the slope is 30 degrees and the coefficient of friction (or friction factor, not sure how it's said in English) is given as u=0.1*(x/m) where x is the path traversed and m is the mass of the object. After...
  5. F

    Friction factor at turbulent region

    Homework Statement in my book , the author stated that the friction factor become maximum when the flow become turbulent ...However , according to the Moody Chart , we can know that the friction factor decreases from laminar to turbulent and then constant ... is the statement in the book wrong...
  6. R

    Why does friction factor decrease with Reynolds number?

    As the flow rate increases frictional force increases but friction factor(Darcy,Fanning) decreases with Re. Can anyone explain what is the concept behind it?
  7. F

    How do I choose the first f_try without given criteria for friction factor?

    Homework Statement is there any criteria when it comes to choosing the first f_try ? Homework EquationsThe Attempt at a Solution in my opinion , there must be at least either relative roughness(ε) given or Reynold number given , so that we can find the first f_try ...But , it is not given in...
  8. T

    Optimization of windmill power with use of gears

    < Mentor Note -- thread moved to HH from the technical Engineering forums, so no HH Template is shown > Okay so I'm a freshman BE student and one of our first projects is designing a windmill that can produce a voltage of 5 for 2 seconds or longer. We are having trouble find the optimal gear...
  9. Dong Aleta

    Approximation of friction factor for Laminar Flow

    Hi! I read from Perry Green's ChE Handbook that the friction factor for Re ≤ 2,100 can be approximated by ƒ = 16/Re. But there was this question that I encountered (though I don't know the source) and according to it, ƒ = 64/Re for laminar flow. Can someone clarify which is which? Thank you!
  10. Dong Aleta

    Friction Factor for Wetted Wall Columns

    Hi! I encountered this problem that asked for the friction factor of a very dilute SO2-air gas mixture in a wetted wall column. All the necessary information were given to compute for the Reynold's number. What I want to know is does having a wetted wall make it a different case (ergo use...
  11. gfd43tg

    Is the Fanning Friction Factor Calculation Affected by Unit Usage?

    Hello, I was wondering if when calculating the fanning friction factor, do english units need to be used? The equation for the head friction is h_f = 4f(L/D)V^2/2 where L is the length, D is the diameter of the pipe, and f is the fanning friction factor. This ends up having units of...
  12. W

    Fluid mechanics, help in finding the dancy friction factor

    How to find the dancy friction factor by using the colebrook white equation (not using the moody chart) ; to calculate the 1/√f = -2LOG[(e/d)/3.71 + 2.51/(Re*√f)] help please
  13. M

    Fluid mechanics: finding friction factor, should be simple

    Homework Statement Given: water at 20°C flows through a 3cmID smooth brass tube at 0.002 m^3/s. Homework Equations V=Q/A f=64/Re Re=VD/(nu) The Attempt at a Solution V=Q/A=(0.002 m^3/s)/((∏/4)*(0.03 m)^2) = 2.829 m/s Re=VD/(nu) = (2.829 m/s)*(0.03 m)/(1x10^-6 m^2/s)=84882.64...
  14. J

    Which Surface Roughness value to use for pipe flow friction factor

    I am trying to predict pressure drop in a pipeline with a range of different materials. I have used a surface profilometer to measure the surface roughness of the different materials and I have values for various surface roughness variables - Ra Rz Rmax Rq Rm S Sm R3z Wt and a range of other...
  15. U

    Ladder leaning against a wall friction factor

    Ladder of mass M and length L leans against a vertical wall. The friction factor between the ladder and ground is K. Calculate the minimum angle at which the ladder can stay in position without slipping off ignoring the friction between the wall and the ladder. Calculating momentum...
  16. T

    Reynolds Number and Friction Factor: How Does It Work?

    So, I understand that when reynolds number increases, the fluid becomes more turbulent, and there is a greater energy loss due to formation of eddies. However, shouldn't this increase in reynolds number cause an increase in friction as well? But, according to the moody diagram...
  17. B

    Finding the Darcy-Weisbach Friction Factor with Limited Info

    Homework Statement I need to find the Darcy Weibach friction factor from the moody diagram but i cannot find reynolds number? All the information i have is K = 0.02mm D = 150mm Q=100 l/s The only formula for RE i found is RE = (density) x (velocity) x (diameter of pipe) /...
  18. J

    Relation between Serghides friction factor and Moody diagram

    Hi All, I'm working on some fluid modeling, and I'm calculating my friction factor using Serghides' method, which, I'm sure you all know, is very accurate in relation to the Colebrook equation. The trouble is, I need to convince my boss that the Serghides equation has merit and is that accurate...
  19. L

    The question is: Where does the blasius friction factor formula come from?

    "blasius" Friction factor I am trying to find out if the formula below can be used to estimate the friction factor for turbulent flows with Reynolds number around 100,000, in an air system. f = 0.079*RE^-0.25 I have not been able to find this exact formula anywhere other than on this...
  20. gmax137

    How Does Friction Factor Relate to Velocity in Fluid Dynamics?

    There's a couple of recent threads on friction - rather than hijack those here's a new thread with a few questions I have. What I'm trying to understand is the relationship between the friction force (on an object moving through a fluid) and the velocity of the object. A few places I see...
  21. N

    How to determine the darcy friction factor for irregular cross section ducts

    How to determine the darcy friction factor for irregular cross section tunnels hi, I needed to calculate the f value for tunnels with these cross section area but I am not sure what are method available to calculate these shapes. Two of those cross section areas are already provided as...
  22. G

    Friction factor and Turbulent flow

    Do the head losses on turbulent flow are always greater then on a laminar flow? Why does it seem from the Moody chart that the friction factor becomes smaller when the flow becomes more turbulent?
  23. H

    Friction factor on very very low reynolds number

    hai all, I'm now doing a research about castor oil. I've a got a few a confusing problems.. 1. to flow castor oil in a 12 mm acrylic pipe i use a reservoir 1 metres from the outlet. Because castor oil is very thick (dyn visc. = 0.5 Pa-m), the velocity of the flow is very low just about 0.02...
  24. B

    Fluid mechanics friction factor formula

    hopefully this will be my last question... My textbook says friction factor = 64/reynold's number for laminar flow. But it doesn't say how this equation is derived. does anyone know where this equation comes from? is it an approximation (i.e. will be more accurate for certain Re's and...