# What is Kinetic friction: Definition and 509 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. ### Question(s) Regarding Magnitude of Force (Window Washer Problem)

So, ignore the -0.72, I was just trying to see if I had a sign error (I then remembered magnitude is absolute value) but basically: Since the weight is 12.0N, theta is 53.1, and the coefficient of kinetic friction is 0.100, I just plugged those values into the equations above...

3. ### Find the Coefficient of Kinetic Friction

Young & Freedman 13th ed, Exercise 7.81 Starting with the crate, here is its free-body diagram: In accordance with Newton's First Law: $$\Sigma F_y = 0 = n+(-w_c \cos{\alpha})$$ Thus ## n = w_c \cos{\alpha} ##. And according to Newton's Second Law:  \Sigma F_x = m_c a_x = w_c...
4. ### How do I find the coefficients of static friction and kinetic friction?

I have found that μstatic= 5.6 (found on graph) / 18.20 = 0.3077 I don't know how to find Force of friction from the graph to calculate μKinetic

None yet
6. ### Confused About Mass? Let's Find Out!

I'm not sure where to start, I feel like I'm missing the mass but it is not listed.
7. ### Equation calculations about the coefficient of kinetic friction

I need an expert to verify equations about the coefficient of kinetic friction.
8. ### Coefficient of kinetic friction

Fn = 53 X 9.81 X cos 22 Fnet = 524 – 53 X 9.81 sin 22 + μ X 53 X 9.81 cos 22
9. ### Equations of motion of damped oscillations due to kinetic friction

Take rightwards as positive. There are 2 equations of motion, depending on whether ##\frac {dx} {dt} ## is positive or not. The 2 equations are: ##m\ddot x = -kx \pm \mu mg## My questions about this system: Is this SHM? Possible method to solve for equation of motion: - Solve the 2nd ODE...
10. ### Does coefficient of kinetic friction depend on speed?

In this part of the lab we pushed a block on a flat table and let it slide until it stopped. So it is decelerating with no force being applied to it while moving. In this case acceleration is negative. The only force acting on it is kinetic friction. Therefore I have come up with the following...
11. ### Pulling masses up a tilted plane with kinetic friction

first, i calculated the kinetic friction: 0.77 x (weight of the 2 boxes x 9.8)= 55.16N then i calculated the angle of the triangle: tan^-1(2.5/4.75)=27.758 then i drew this then i used sine to find out force 3 which is 33.3556 so the final force needed is 33.3556 + kinetic friction=...
12. ### Is Kinetic Friction a Conservative Force?

If a block slides down an inclined surface under the presence of the kinetic friction, does that mean the total energy lost by the block is equal to the work done by the kinetic friction? Thanks in advance.
13. ### 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...
14. ### Difference between static and kinetic friction

I always read that the static friction applies when the object is not moving. If it starts moving then you have kinetic friction. But suppose the case of a block on conveyor belt. The block is moving, but I was told that that friction was static friction. Or suppose the Death Wall. I've also...
15. ### 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?
16. ### Finding the coefficient of kinetic friction - problem with a mass on a plane

I don't really know how to begin this problem. I need some advice
17. ### Inclined Plane Problem with Kinetic Friction

I tried to find the force of friction using the the coefficient of kinetic friction with the equation F=nukmgcos Ѳ. Then I made the force of friction equal to the force of pull. I don't know what I'm doing wrong as I'm getting the wrong answer. I have attached a picture of my work.
18. ### Calculating acceleration from the coefficient of kinetic friction

Homework Statement At a construction side, a small crane is raising two boxes of nails on a plank to the roof. One box has already been opened and is half full, while the other box is new. The boxes, including the nails, weight 10 kg and 20 kg, respectively, and are the same size. Diagram...
19. ### Determine the friction force in a stacked block scenario

Homework Statement Assume that block A which has a mass of 30 kg is being pushed to the left with a force of 75 N along a frictionless surface. What is the friction force of block A on block B if the block B has a mass of 24 kg and is accelerating at 0.50 m/s2 to the right relative to the block...
20. ### What's the coefficient of kinetic friction?

Homework Statement : A sled starts from rest at the top of a snow-covered incline that makes a 20° angle with the horizontal. After sliding 68 m down the slope, its speed is 17 m/s. Use the work–energy theorem to calculate the coefficient of kinetic friction between the runners of the sled and...
21. ### Motion when Kinetic Friction is more than Static Friction

Homework Statement How would the motion of the block look like when the Force of kinetic friciton is more than the Limiting value of static friction? Homework Equations Kinteic Friciton=μN The Attempt at a Solution I think the block after overcoming the limiting value of static friction will...
22. ### Kinetic friction direction on two stacked blocks

If i have two blocks on top of each other and there is friction between the two blocks and it's a kinetic friction ( given μk). if i was given the force applied on the lower block to the right direction for example. ignoring the friction between the lower block and the ground, i tried to draw...
23. ### Static and Kinetic Friction vs Normal Reaction Graphing

How do i suppose to determine the uncertainty for the slope of my Static friction against normal reaction graph? My data for static friction and normal force has the uncertainty of +/- 0.0001 The uncertainty is too small for me to draw airbox/bar in the graph to draw the max and min slope...
24. ### How to find the coefficient of kinetic friction

Homework Statement The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is: A) 0.062 B) 0.25 C) 0.41 D) 0.62 E) 1.2 Homework Equations I'm not too sure but i know that : If the...
25. ### Kinetic Friction Homework Help

A steel washer is suspended inside an empty 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 37 above the horizontal. The crate has mass 154 kg. You are sitting inside the crate; your mass is 61 kg. As the crate is...
26. ### Coefficient of kinetic friction lab

Homework Statement I need to find the coefficient of kinetic friction from a set a lab data that I found. I had a mass connected to a mass hanger by a pulley, and measured the acceleration of the mass with various amounts of mass on the hanger. In the attached image, the acceleration was...
27. ### The coefficient of kinetic friction for a Ford Focus

Hi guys, Yesterday I sat down, and just for fun, decided to calculate the coefficient of kinetic friction for the all electric Ford Focus. I keep getting the wrong answer, and it is driving me crazy. Here are the facts. Battery: 23 kWh. Curb weight: 1,651 kg. Maximum travel distance before a...
28. ### Finding the coefficient of kinetic friction on an incline

<< Mentor Note -- Two threads on the same subject have been merged >> I am a junior enrolled in IB Physics at the standard level at my high school. As a part of the curriculum we must perform an Internal Assessment (IA) which involves performing an experiment and performing calculations and it...
29. ### How to get the coefficient of kinetic friction?

Homework Statement Homework Equations W = Fk d cos θ Fk = FN μκ The Attempt at a Solution Here's my work : m = 1 kg vi = 10 m/s vf = 0 m/s xi = 0 m xf = 0.1 m d = 0.1 m k=60 N/m μκ=? The work done be the frictional force : W = Fκ d cos θ = FN*μκ*d*cosθ = mg μκ d cos 180 =...
30. ### How to get the coefficient of kinetic friction

Homework Statement Homework Equations W = ΔUg + ΔkE + ΔUs KE = 0.5 m v^2 Ug = m g h Us = 0.5 k x^2 The Attempt at a Solution k = 60 N/m vi=0 m/s (" the block is released from rest ") xi= 0 m/s ( "the spring is unstreached") vf= 0 m/s xf= 0.2 * sin 37 = 0.2*0.6 = 0.12 m d= 0.2 m...
31. ### How does kinetic friction occur between two moving bodies?

Could anybody explain what happens at the molecular level when one of the two bodies in a contact starts moving w.r.t other, i mean in this process what causes kinetics friction force, i tried myself to think of it but i could not come up with any, so please help me.
32. J

### Coefficient of kinetic friction?

Homework Statement A 2.79-kg block is placed on a rough surface inclined at 28.1°. The block is launched at a speed of 3.87 m/s up the incline, and comes to rest after sliding 0.969 m up the incline. Find the coefficient of kinetic friction between the block and the incline. Homework...
33. ### Acceleration of object with friction: Homework help

A 50 kg box rests on the floor. The coefficients of static and kinetic friction are 0.70 and 0.50, respectively. a.) What is the minimum force required to start the box sliding from rest? b.) After the box starts sliding, the person continues to maintain that force. What is the...
34. A

### Finding work and the Change in Thermal Energy

Homework Statement Kerry is pulling a 156-kg sled along a snowy, horizontal path with a 620-N force directed at an angle of 29.0° above the ground. He pulls the sled over a distance of 26.0 m, and the coefficient of kinetic friction between the sled and the ground is 0.0622. I need to find the...
35. A

### Static and kinetic friction help?

I found a problem and I'm having one question, it goes like this: A box of 5 kg is being dragged across the floor with a horizontal force of 40 N. If it starts at rest and it begins to accelerate at 3 m/s2 (constant acceleration), find: A) The coefficient of kinetic friction B) Supposing that...
36. M

### Kinetic Friction Between Block and Surface (HW Check)

Homework Statement A 10 g bullet is fired at 200 m/s into a 1 kg block after which they slide together 2 m on a horizontal surface. Determine the coefficient of kinetic friction between the block and surface. Homework Equations ##M_AV_{Ai} + M_BV_{Bi} = 0## ##WNC = ΔE## The Attempt at a...
37. B

### How do I find the the coefficient for kinetic friction given

A 10.0 kg box rest on a horizontal board. One end of the board is slowly raised to 12.8° with the floor, the box slides at a constant velocity. (Use this information to find the kinetic coefficient). Find the magnitude and direction of the acceleration of the box when the board is raised to an...
38. 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...
39. ### Work done by kinetic friction

Homework Statement A 5.72 kg block is released from rest on an inclined surface. The incline makes an angle of 25.0 degrees relative to horizontal. The block is known to be traveling at a speed of 1.33 m/s after sliding a distance of 2.60 m along the incline. How much work was done on the block...
40. ### How to use the coefficient of kinetic friction?

Homework Statement A child is playing with their Hot Wheel cars. They have set up a track which is initially horizontal but then ascends to a second horizontal section which is 50 cm higher than the initial track. The track is friction-less until the car reaches the upper section of the track...
41. ### Calculating Forces and Kinetic Friction for a System of Connected Blocks

Hi everyone, I'm having a difficult time figuring out this problem. Could someone give me some pointers? I set up the equations and the free body diagrams (hopefully they're correct) ; all I have to do now is solve for F.1. Homework Statement A block of mass m is on top of a block of mass M =...
42. ### Average Coefficient of Kinetic Friction between Ice and Puck

1. The problem: A hockey puck is hit on a frozen lake and starts moving with a speed of 11.6 m/s. Five seconds later, its speed is 7.4 m/s. What is its average acceleration? The acceleration of gravity is 9.8 m/s. Answer in units of m/s. What is the average value of the coefficient of kinetic...
43. ### How to find Coeff of kinetic friction without mass?

Homework Statement For my Physics lab this is what my teacher handed me... I have no idea how to attack the situation, can someone help solve? Devise a procedure for an experiment which will measure the coefficient of kinetic friction between a block of unknown mass m and the table, where the...
44. ### Find coefficient of kinetic friction of block and ramp.

Homework Statement A small block is on the point of slipping down a rough ramp inclined at 35 degrees to the horizontal. a) What is the coefficient of static friction between the block and the ramp? Answer μ_s = 0.70 b) The ramp is attached to the edge of a 0.8 m high table. After the block is...
45. ### Finding the force of kinetic friction without a coefficient

Homework Statement In a lab assignment we created a Fletcher's trolley system and were asked to calculate the normal force, the force of friction, and then create a graph of both to find the coefficient of kinetic friction. So far, the variables I have are: Hanging mass: 0.100 kg Sliding...
46. ### How Long Does It Take for the Block to Reach the Other Side?

Homework Statement A small block of mass 1.74 kg rests on the left edge of a block of length 3.05 m and mass 7.95 kg. The coeﬃcient of kinetic friction between the two blocks is 0.279, and the surface on which the 7.95 kg block rests is frictionless. A constant horizontal force of magnitude...
47. ### Understanding Work and Energy: Solving a Physics Problem

I have been stuck on this physics question: An object is sliding along a flat surface with an initial speed of 30 m/s. What must the coefficient of kinetic friction be between the object and the surface if the object slides to a stop in 10m? What would be the speed of the object after it had...
48. ### Friction Lab? Kinetic Friction?

Homework Statement Hi, we had a Lab Activity on the Coefficient of Friction, but right now I am really confused and stuck. Since the teacher used an online resource, we are supposed to make two graphs based off the data and it's very unclear and unhelpful. :( I can't seem to find anything at...
49. ### How can I calculate kinetic friction?

Homework Statement A child slides down a slide with a 28 degree incline , and at the bottom her speed is precisly half what it would have been if the slide had been frictionless. Calculate the coefficient of kinetic friction between the slide and the child. Homework Equations Newtons second...
50. ### How to find the coefficient of kinetic friction?

Homework Statement A child slides down a slide with a 28° incline, and at the bottom her speed is precisely half what it would have been if the slide had been friction-less. Calculate the coefficient of kinetic friction between the slide and the child. Knowns: 28° speed=V/2 Homework Equations...