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.
I teach a first year Physics course. The incoming students (grades 10-12) have little to no Physics background. We are making some modifications to our work and energy unit. One modification that has been discussed is what to do about kinetic friction. At present, we account for friction as a...
A 30-cm-diameter, 1.6 kg solid turntable rotates on a 1.4-cm-diameter, 450 g shaft at a constant 33 rpm. When you hit the stop switch, a brake pad presses against the shaft and brings the turntable to a halt in 15 seconds.
How much friction force does the brake pad apply to the shaft?
I am...
Background question:
A bicycle and rider have a combined mass of 75 kg. They freewheel down a slope whose maximum height is 6 meters above sea level. The slope is 20 meters long. At the end of the slope, the bicycle and rider are traveling with a velocity of 10 m/s. Calculate the work done...
I'm interested in finding out what the coefficient of friction would be for a few different materials such as:Copper on aluminum
Copper on graphite
graphite on aluminum
I'm not sure if it matters if the order is reversed such as Aluminum on copper vs copper on aluminum..
also I've seen that...
So... I've been thinking in time manipulation "super powers" for at least three years. First i just thought "well, you have to drain time from things, don't you?" then i learned basic physics and i thought "well... that was kind of unrealistic, one actually should accelerate to a % of the speed...
Homework Statement
Homework Equations
The block has potential energy U at the top of the ramp, and this is transferred to kinetic energy K at the bottom, which is then trasnfered to work done by friction, Wfr.
U = K Conservation of energy
K = Wfr Conservation of energy
g = 10 m/s2The Attempt...
Homework Statement
A car drives along a curved track. The frictional force exerted by the track on the car is:
a. greater than the frictional force exerted by the car on the track
b. directed radially outward
c. opposite in direction to the frictional force exerted by the car on the track
d...
Homework Statement
A box of mass m is set on a merry-go-round of radius r with a linear speed v. The friction coefficient between surfaces is μ.
Homework Equations
ac = v²/r
The Attempt at a Solution
I imagined this problem because I'm trying to understand more deeply circular motions. I have...
I'm studying boundary layers. I am confused by what I am reading in this book.
The book says the friction force (F) per unit volume = $$\frac{dF}{dy}=\mu\frac{d^2U}{dy^2}$$
They say $$\frac{dU}{dy}=\frac{U_\infty}{\delta}$$
This makes sense to me, delta is the thickness in the y direction...
Hi,
Please see the attach picture.
I solved 3 quetions regarding this problem and I struggle with the 4th one.
What I found was that the initial velocity after the collision is 1.98 m/s (Edit: 0.2m/s), and the maximum compression of the spring with no friction beneath is 0.44m (Edit: 0.044m) (I...
Homework Statement
A 50kg object begins at rest on a surface with a static coef of friction at 0.6. If you push horizontally on the object with a force of 27N, how quickly will it move across the surface?
Homework Equations
The Attempt at a Solution[/B]
This is from Trivium Praxis test prep...
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...
Homework Statement
We have a 200-LB door hanging from 2 rollers, A & B, which are 5 feet apart. Coeffs of friction for A and B are .15 and .25, respectively. A force P is applied to the door. How big must it be to move the door to the left?[/B]Homework EquationsThe Attempt at a Solution
I...
Homework Statement
A block of mass 100 grammes was stationary on the flat surface at ##x = 0##. At
time ##t = 0## a horizontal force of 10 Newtons was applied on the block in the
positive x direction during ##\Delta t = 3## seconds.
Find at what x position the block will stop, if the...
Homework Statement
So In the following picture is the problem and its solution (Problem 130)
Homework Equations
KE =1/2 m v2 x:=w^2x
The Attempt at a Solution
I am confused of the fact that the time from the spring touching t2 is T/4-t where T is the period oscillations while t is the time to...
Problem :
A car of mass ##m## is parked on a slope.
What does static friction ##\mu_s## have to be for the car not to slide down if
the incline of the hill is ##30## degrees?
*******
For this problem I have the following forces, where the hill is inclined upwards
to the right:
Upwards ...
I would like to check my understanding for this problem :
A puck with mass ##3m## is stationary on a horizontal friction-less surface. It is
being impacted in an elastic head-on collision by another puck with the mass
##2m## traveling with speed ##u## to the right. Find the speed and direction...
Homework Statement
A rotating flywheel slows down only because of friction in its bearings. At the initial time ti, the angular speed of the flywheel is 2.0 rad/s. The power due to friction at a later time tf is half of the power due to friction at time ti. The angular displacement of the...
Homework Statement
A 1.0x10^3 kg elevator carries a maximum load of 800kg
Velocity = 3m/s
Distance = .01km
Net work = 13640J
Homework Equations
Force of friction = (m)(mu)(gravity)
The Attempt at a Solution
Gravity = friction
9.8 = (mu)(17640)
.001 = mu
Homework Statement
A boat of mass 1000 kg is moving at 25 m/s. The friction force ##f## is proportional to the speed ##v## of the boat, ##f = 70v##. How many time will take for the boat to reduce its speed to 12.5 m/s?
Homework Equations
##\vec{F_r} = m \vec{a_r}##
The Attempt at a Solution...
Homework Statement
I have a Force Normal vs Force Friction Graph and I wan to find the coefficient of friction from the graph.
Homework Equations
The Attempt at a Solution
I have tried the formula ff= uFN but my teacher is looking for me to do it using the graph
In my experiments, on a flat plane, when I incrementally increase the normal force acting on a rubber block, I am measuring a decrease in the static coefficient of friction. I am also measuring the friction force, which increases as normal force increases BUT this is not a proportional increase...
Let's say you two objects with weight of 2 kilograms but one is narrower and one wider. They are said to be similar coefficient of friction against a surface.. but what if the surface is rough? Won't the wider object has more friction?
Or still the same?
If still the same.. what if the...
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...
I am aware that there needs to be two materials for there to be a coefficient of friction, but I mean in general. For example, I know synthetic setae are very resistant to slipping on surfaces.
This issue was the subject of this old post, now closed.
The question is: can a coefficient of friction (static) be larger than one?
I see confusing replies. Someone talks about glue, but I'm not convinced about that. It's a bit like wondering about the coefficient of friction of a wooden plank...
(mentor note: moved here from a non-homework thread)
Hello
I am trying to find the time it will take for a parcel to pass over one conveyor belt
The conveyor on the right is Conveyor A The conveyor on the left is Conveyor B
they both have a length of 700mm
Conveyor A has a constant speed of...
Homework Statement
Vo = 5m/s
W to the left = 6N
Ffriction = 2N
F to the left = W - Friction = 4 N
m = 1kg
g = 10 m/s^2
Ramp length = 10m
sin a = 3/5
cos a = 4/5
Homework Equations
F = ma
Vt ^2 = Vo^2 + 2as
Vt = Vo + at
The Attempt at a Solution
Outside force (1) to cancel acceleration from...
Hi Guy's, I'm starting a project to explore the physics of hysteresis friction between two surfaces.
One flat metal surface is considered to have zero compressibility but does have grooves interrupting the sliding action.
The second material (organic elastomeric compound) also having a flat...
Homework Statement
The 1.0 kg block in the figure is tied to the wall with a rope. It sits on top of the 2.0 kg block. The lower block is pulled to the right with a tension force of 20 N. The coefficient of kinetic friction at both the lower and upper surfaces of the 2.0 kg block is μk = 0.300...
Homework Statement
I am investigating a scenario where a pendulum with a bob attached is released from an angle and pushes a box to a certain distance. My goal is to find the coefficient of friction between the box and the surface it moved on.
I have measurements for:
- mass of the bob (125...
Homework Statement
A sledge of mass m1 is pulled horizontally with a force F. On the sledge there is a body of mass m2 that can slide on the horizontal platform of the sledge with the friction coefficient μ. Another sledge of mass m3 is tied with a horizontal string of the body m2. Between the...
Greeting fellow physicists,
I have been having some questions from my AP Physics C: Mechanics students about the direction of friction in rolling. Here are a few situations.
1. For a wheel that is accelerating to the right while rolling smoothly, it must also be rotating clockwise. In order to...
From Painleve we know that Coulomb's law of friction being applied to rigid bodies systems may produce contradictions. Painleve constructed several examples of such contradictions, so called Painleve's paradoxes, see [Painleve P. Leçons sur le frottement. P.: Hermann, 1895]. Those examples...
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...
Homework Statement
Block A, with weight 3w, slides down an inclined plane S of slope angle 36.9 degrees at a constant speed while plank B, with weight w, rests on top of A and is attached by a cord to the wall. If the coefficient of kinetic friction is the same between A and B and between S...
If I push an object such as a cylinder of wood along a flat table (flat face of cylinder in contact with the table) through it's center of mass, the friction or energy required is not dependent of the surface area the block makes with the table, Friction = μ N, correct? And the energy required =...
Question: If a 1000kg Mass resting on a friction free airbed is accelerated from zero to 1 Metre per second by a drive motor, then the motor is disconnected, how much electrical braking energy could be recovered from the moving mass in percentage terms using modern technology. Thank you in...
Hi there,
I was thinking that static friction works in opposition to a reaction force like the force of a fridge against you as you push it. However, since you are pushing horizontally and friction works against you why is it equal or greater than the reaction force? Will the force get...
Hello, I have been learning about energy and work in my 100 level physics class and I got to thinking:
W = F*d
But I'm wondering how this works in the case of static friction. For instance, if I take a really heavy object and apply a force to it that isn't enough to move it, the distance it...
Is there any case example where the friction force DOESNOT oppose the motion, but rather PROVOKES the motion of some object?
I wondered about this all day long :D
Homework Statement [/B]
In an automatic materials handeling operation, metal blocks of 1.5 kg each are pushed one at a time from bottom of a stack six blocks high. If the coefficient of friction is 0.25, determine the horizontal force required to push. There is a figure bellow.
I try to...
In a classic problem where a man walks along the length of a boat floating on the surface of water without friction, Should the net work done due to static friction between the man and the boat be zero. If the length of the boat is L, its mass being M, and the mass of the man being m, the...
Question:
A large box of mass M is pulled across a horizontal, friction-less surface by a horizontal rope with tension T. A small box mass m sits on top of the box. The coefficients of static and kinetic frciton between the two boxes are Us and Uk. find an expreeion for the maximum tension Tmax...
Homework Statement
An disk has a radius of 0.2 meters. A lump of putty with a coefficient of static friction of 0.9 is stuck on the edge of the disk.
Let's say the disk starts at rest and gradually speeds up. At what speed will the putty just barely be able to stay in place on the edge of the...
Hello! I am an AP Physics student and had a quick question for validity. I was prompted with this question in class today:
Example 7: An 8-meter ladder of weight 355 N leans at an angle of 50° to the floor against a smooth vertical wall. Assume the center of weight (gravity) for the ladder is at...
Homework Statement
Consider a uniform solid disk of mass m and radius R, rolling without slipping down an inclined plane with an angle γ to the horizontal. The instantaneous point of contact between the disk and the incline is called P.
Homework Equations
ma = mgsinγ - μmgcosγ
Γ = Rmgsinγ-Rμmg...
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 =...
I thought this would be the most logical way to post this, but give me some grace if it is not because this is my first time posting on this site (then relinquish the grace and tell me how to do it properly haha).
First: When a physics problem says "sliding past point P" does that mean it stops...