What is Force of friction: Definition and 140 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. arhg

    A Normal force and force of friction inside a tube

    Dear all, Me and some colleagues (non-physicists) are discussing how force works when passing a cylinder (which we are holding) into a narrow tube. As we insert more of the cylinder into the tube, the force we are exerting is increasing. My theory is that the normal force is increasing and his...
  2. zstraught

    Question about work and finding the force of friction

    I drew a force diagram, Normal force up, weight down, force of friction to the left, and Force applied 20 degrees above the positive x axis. I need clarification to find the force of Friction for part B. Should I set Force of friction equal to mu · normal force or should I use Newton's second...
  3. 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?
  4. C

    Spring force and the force of friction

    Hello, do someone have time to help me out with an assignment? My question In the answer sheet they say: What I do not understand is why m is withdrawn from both sides, since I don't see that those represent the same mass. When I did the assignment I thought m at the left side would be the...
  5. W

    Find the force of Friction and minimum coefficient of friction

    Fg = mg = 50 * 10 = 500 N Fn = mg-ma = 500 - (50.0)(1.0) = 500-50 = 450 I don't necessarily know if this is right and I can't seem to find the Ff or coefficient of friction either. Please Help!
  6. C

    Force of friction in turning cars

    I read an article where the author tried to find the maximal speed a car can have when taking a turn of certain radius. They represented the car as a point and claimed that the force of friction is the centripetal force - acting perpendicular to the trajectory of the car. I do understand why...
  7. isukatphysics69

    Block pushed up against wall, determine the force of friction

    1. Homework Statement I have already solved this one weeks ago, and i have a test Tuesday so i was reviewing these problems. I understand everything when solving with 60N as the force.. but then when i changed the force to 20N, i had to use the coefficient of kinetic friction to get the correct...
  8. Jamesgortrig

    Is the work caused by the force of friction negative?

    Homework Statement A student pushes a 0.65kg box Ali g a desk. When he stops pushing the book, it moves 85cm before stoping (slowing down in this period). Coefficient of friction between book and Table is 0.27.Calculate the work done on the book by the friction. Should it be positive or...
  9. H

    How does the reaction force of friction affect the ground?

    Suppose I am trying to push a heavy block on ground and I haven't applied a force stronger than the maximum static friction. The force of friction acts on the block and its equal and opposite force acts on the ground. Does the reaction force of friction(acting horizontally on the ground)...
  10. C

    Calculating Frictional Force on a Roller Coaster: Solving for Final Velocity

    Homework Statement Ok so there was a question on a physics quiz I did that I have no idea how to answer. There was a roller coaster going down a hill with an initial velocity of 1.67m/s. The hill is 60m long and had an angle of 40 degrees. There is a coefficient of friction of 0.100 with the...
  11. J

    Find Coefficient of Friction: Force of Friction Homework

    Homework Statement Mass: .034kg Acceleration: -.3644 Time:2.744sec Inital Velocity: 1m/s The path is on a flat surface Homework Equations Ff=mu(Fn) F=m*a The Attempt at a Solution I need help find the coefficient of friction. I'm trying to find the difference of mu between oil, water, and a...
  12. T

    How to Find Force of Friction and Acceleration?

    Homework Statement Hey, guys I'm having trouble solving this problem, I'm not sure what to do first This is the info it gives: A stationary 15 kg object is located on a table near the surface of the earth. The coefficient of static friction between the surfaces is 0.40 and the coefficient of...
  13. M

    MHB Force of Friction: 0.5kg Ball & 0.381m Net

    Suppose that the ball exits the net going straight down at a velocity of just 0.600 m/s. What is the force of friction between the net and the ball, provided that the net contacts the ball throughout a length of 0.381 meters? The mass of the ball is 0.5kg. (The approximate answer is 9.0N) I...
  14. K

    Distance to Come to Rest and Force of Friction

    Homework Statement The coefficient of static friction is 0.625 between the two blocks shown. The coefficient of kinetic friction between the lower block and the floor is 0.137. Force F causes both blocks to cross a distance of 4.46m, starting from rest. What is the least amount of time in which...
  15. TyroneTheDino

    Conceptual Question about Static Friction

    Homework Statement Today we were studying a block on an incline and determining the angle needed for the block to start sliding. The question asked is: Why is the equation for the coefficient of static friction independent of the weight of the block? Homework Equations ΣFx=Fapplied-fs=0...
  16. S

    Calculate force of friction on car as it rolls across

    Homework Statement Calculate the force of friction on a toy car as it rolls across a flat floor. Given: mass = 0.293kg time = 3.66 s displacement = 8.7Homework Equations Fnet = mass x acceleration displacement = [(velocity1 + velocity2)/2] time velocity2 = velocity1 + acceleration(time)The...
  17. P

    Force of Friction: Stopping 1,000kg Car at .8 Coeff.

    A driver of a 1,000kg car is traveling at a speed of 30m/sec when he sees an obstruction in the road. It takes driver .75sec to apply foot to brakes. The car begins to slow down at max rate possible for a coefficient of friction of .80 between the road and tires. My question is: what is the...
  18. M

    How to find the force of friction?

    Homework Statement What is the force of friction on the elastic powered car as it rolls across a smooth surface? GIVENS Displacement= 16.25m, Change in time= 22.5s, G=9.8m/s, Mass= 1kg UNKNOWNS V1=?, A=? Ff=? Homework Equations F=MA, A=V/T, Change displacement=((V1+V2)/2)T) The Attempt at a...
  19. C

    Determining Coefficient of Kinetic Friction w/m, t, and v

    Homework Statement A 2.0 kg block of wood slides over a horizontal surface and comes to rest in 2.5 s. If its initial velocity was 9.0 m/s, what is the coefficient of kinetic friction? Homework Equations rho=mv change in rho=F*change in t Force of friction = mu*Force normal Force normal=mg...
  20. M

    Find the force of friction provided by the floor

    Homework Statement Please see attached picture. Homework Equations Ff=uFn[/B]The Attempt at a Solution I'm really not sure where to start, since I don't know the coefficient of friction. Fn = ma Fn = 0.1kg(9.8m/s^2) Fn = 0.98N Does this mean that the force in the image is 0.98N as well...
  21. A

    Force of Friction on Boat w/ Thrust

    Homework Statement A boat moves across the water at a constant 30 mph towards the west. If the motor is generating a thrust of 500 M then the force of friction on the boat must be... a. 500 N to the east b. 500 N to the west c. less than 500 N to the east d. less than 500 N to the west...
  22. K

    Find the average force of friction

    Homework Statement A 5kg box is tossed across the floor at 4 m/s and slides to a stop in 3 seconds. What is the average force of friction? Homework Equations I believe the answer is 6.66N, I found that because the problem was pulled from the book. But I am trying to understand how and why...
  23. S

    Force of friction on a curved road

    Homework Statement The mass m car is traveling at v on the straight portion of the road and then its speed is uniformly reduced from A to C, which point it comes to rest. Compute the magnitude and direction of the total friction force F exerted by the road on the car (a) just before it...
  24. F

    How do I calculate mass of pulley and force of friction on AtwoodMach.

    Homework Statement Basically, I need to calculate the mass of the pulley and friction using data that I collected. Homework Equations I was given: (m1 - m2)g = (m1 + m2 + mp)a + f The Attempt at a Solution For the first part, I collected data using a sensor to find the...
  25. P

    Calculating the force of friction on an object

    Homework Statement A 40.0-kg object is being pulled along a horizontal surface by means of a rope that exerts a force of 200 N at an angle of 30° below the horizontal. The coefficient of static friction between the object and the surface is 0.40. The force of friction on the object is: A) 197...
  26. R

    Magnitude of the Force of friction

    Homework Statement A child pulls a wagon at a constant velocity along a level sidewalk. The child does this by applying a 22-Newton force to the wagon handle, which is inclined at 35° to the sidewalk. What is the magnitude of the force of friction on the wagon? Homework Equations Ff =...
  27. F

    Discrepancy in force of friction in a problem

    Homework Statement Here is the problem: A student pushes a 5.0 kg block at a constant speed 3 m across the ceiling of her room using a force Fa of magnitude 85 N and angle 75º. The coefficient of kinetic friction between the block and the ceiling is 0.40. Now, we must find the work done by...
  28. F

    What Forces Act on a Box Moving Up a Frictional Ramp?

    Homework Statement A 25kg box of books is pushed up a ramp and into the back of a pickup truck. The box-ramp system has coefficients of friction (static = 0.6, kinetic = 0.45). The ramp is placed at the maximum angle possible with respect toe the horizontal before the stationary box would...
  29. N

    Mass on Bridge, Find Force of Friction when bridge is barely inclined

    Look at the picture attached. There is a mass on a drawbridge, which is inclined at half a meter. We have the Normal force, the coefficient of static friction, force of gravity and the force of friction pushing the mass upwards to the end of the draw bridge that is most inclined. We also have...
  30. T

    Calculating Force of Friction: A Homework Help Guide

    Force of friction help! Homework Statement A force of 755N is exerted on a rope to pull a 45.0N wooden crate across a concrete floor. If the rope makes an angle of 35.0° with the floor and the crate is moving at a constant velocity what is the amount of the force of friction? Homework...
  31. F

    Find the energy lost at the collision and the average force of friction

    Homework Statement We have to make a roller coaster for our school project. This coaster starts with a spring. In this coaster, there is a collision. Essentially, I need to find the energy lost at the collision, and the average force of friction. Homework Equations Em1=Em2 W=Fd F=ma A=DELTA v/...
  32. K

    How Do You Calculate the Force of Friction on a Moving Cart?

    Homework Statement A 6.5 kg cart is pushed along a horizontal surface with a rightward force. After the cart is pushed a distance of 3.5 m starting from rest, its speed is 6.0 m/s. Find the force of friction acting on the cart. Homework Equations W=fd (?) KE= 1/2(m)(v)^2 (?) F_net=ma...
  33. H

    How to find applied force when given force of friction (constant velocity)

    Homework Statement Five dogs, each having a mass of 30kg, pull a 250kg sled horizontally across the snow (coefficient of kinetic friction = 0.14). How much force must each dog exert in order to move the sled at a constant velocity? Homework Equations Force of kinetic friction =...
  34. W

    Understanding Force of Friction on Inclined Planes: Calculating μ and Ff

    I am having a little trouble understanding the force of friction. It is given by the formula Ff = \muFN Now taking a mass on an inclined plane with angle θ into consideration, I want to find out what the value for μ. I know what FN is I can easily calculate that but I am having trouble...
  35. L

    Help with Vectors: Force of Friction problem

    "Mr Mcgoo pulls a sled with several children on it at a constant speed. If he pulls with a force of 329.461 N at an angle of 17° above the horizontal, what is the force of friction on the sled?" Not sure if i even drew the picture right(is it like a triangle, but it doesn't say hill...
  36. C

    Force of friction on different times

    Homework Statement A 3.280 kg block of wood rests on a steel desk. The coefficient of static friction between the block and the desk is μs = 0.605 and the coefficient of kinetic friction is μk = 0.155. At time t = 0, a force F = 12.0 N is applied horizontally to the block. State the force of...
  37. A

    Basic Force: Why to take force of friction from force applied y?

    Homework Statement A box of books weighing 319 N is shoved across the floor by a force of 485 N exerted downward at an angle of 35^degrees below the horizontal. a) If uk between the box and the floor is 0.57, how long does it take to move the box 4.00 m, starting from rest. b) If uk...
  38. A

    How to determine the force of friction from a graph?

    Homework Statement I had to a lab on the Newton's second law of motion, and one of the direction was to "determine the force of friction" from a graph I constructed. The experiment is similar to this: http://people.sc.fsu.edu/~dduke/manual/gp1.htm This image of the data is a lot cleaner than...
  39. Q

    2D Friction-Finding the Force of Friction without Mu

    2D Friction--Finding the Force of Friction without Mu Homework Statement A 1500kg car is parked on a 4-degree incline. The acceleration of gravity is 9.8 m/s2. Find the force of friction keeping the car from sliding down the incline.Homework Equations FW=mg [Sigma]Fy=0, so Top=Bottom "Friction...
  40. A

    Calculating resultant force of friction from rope and bar.

    Hello, I hope this is a suitable forum, it's a million miles from homework but it may be on the same sort of level. A picture is worth a thousand words so please have a look at the attached picture. When the rope is pulled there isn't just the issue of gravity, but also of the friction of...
  41. B

    Relating terminal velocity, force of friction.

    I was working on problems for the MCAT and came across this below. After a few minutes working, I had couldn't come up with the solution. Usually the answer clears up any questions I have, but I'm having trouble figuring out how the force due to gravity matches the force of friction. I thought...
  42. K

    Velocity, Force of Friction, and Total Energy in a System Question

    Homework Statement A 200 kg boulder falls from rest off a 120.0 m high cliff. If the boulder experiences a frictional force of 280 N[U] as it falls, what would be the velocity just before it hits the ground? Homework Equations kinetic energy = (1/2)mv2 gravitational potential energy =...
  43. R

    Finding Force of Friction - Tug of War Problem

    Homework Statement Joe and Bill are playing tug of war. Joe is pulling with a force of 200 N. Bill is simply hanging on, but skidding toward Joe at a constant velocity. What is the force of friction between Bill's feet and the ground? A) Greater than 200N but less than 400N B) Less than...
  44. D

    Direction of the work done by force of friction

    Topic : Direction of the work done by force of friction Consider a case when a block is placed on a horizontal platform at rest. It then starts accelerating with a constant acceleration such that, Friction present between the block and the horizontal platform > mass times its acceleration...
  45. P

    Understanding Friction: Formula and Meaning Explained

    Homework Statement What's the friction's formula, and what do the formula pieces mean, thanks :) Homework Equations none The Attempt at a Solution none
  46. P

    Homework help (Force of friction)

    Homework Statement We have a body with force ##F=10N##. Now we know Force of friction makes the body not move if the Force of friction ##F_f## is higher than the normal force ##F_n##, so what force of friction do we have to depress to make the body move 2. The attempt at a solution We...
  47. S

    Force of Friction w/o Coefficient of Friction Given

    I am having trouble determining what the force of friction of the box on a table described as below: Two blocks are arranged at the ends of a massless string. M1 is on the table. M2 is attached to another side of the rope hanging off of the side of a table with a massless pulley (90 degrees...
  48. A

    Solve Car Acceleration: Force of Friction Homework

    Homework Statement A 1250 kg car traveling at 60.0 km/h comes to a sudden stop in 35 m. What is the coefficient of friction acting on the brakes? HOW WOULD YOU FIND OUT THE ACCELERATION OF THE CAR? Homework Equations Fr= μN Fn= ma The Attempt at a Solution I'm stumped on how to...