# Questions tagged [friction]

The resistance a surface or object encounters when moving over another.

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### Why work done by friction is positive? [closed]

Imagine a chain of mass m hanging from a table(not frictionless) which slips down the table. I want to calculate work done by friction. Obviously as it opposes slipping it should be negative. However ...
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### What happens when an expression for a physical quantity becomes undefined?

Now I am taking a quite a specific example here. Let's consider a circular race track banked at an angle of $\theta$. The coefficient of friction between the track and the tire is $\mu$. What's the ...
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### What wears out a rubber sole of a shoe faster - sliding against dry or wet clay?

This question arises from my daily experience as a tennis player. I'm a novice to tribology. I couldn't quite come up with anything to answer that question. Any help? I know for certain that the ...
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### A box sits on a table at rest and is not about to move. What can you say about friction force? [closed]

A box sits on a table at rest and is not about to move. Which one of the following is a correct statement? a) The normal reaction of the table on the box is equal to the mass of the box b) The ...
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### Would it be possible to create a perpetual motion machine in an environment without air, friction, or dissipation?

Perpetual motion machines don't work because as it moves, the air molecules hit it and slow it down. Friction slows it down in a similar way. If there were no forces to slow it down, could it work?
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### Are Newton's first and third laws contradictory?

Newton's first law states that given an ideal situation, any force applied on a body would change its state of motion and the object would continue to pursue that state, given no other force acts on ...
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### How does the friction affect force, angular acceleration on a rolling body

When a mass rolls without slipping on an inclined plane, does the frictional force impart an angular acceleration whilst taking linear momentum out of the mass? Does the frictional force reduce the ...
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### Is terminal velocity applicable in the horizontal plane?

Is there a speed that object A can move at, such that object B would remain 'stuck' to the front of object A, due only to the air pressure as a factor of object A's speed? I realise that friction ...
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### If electromagnetic field is long range then why friction works only for contacting surfaces?

I know that friction is cause by the electromagnetic force between electrons from 2 contacting surfaces but how come it only applies to physical contact with a solid surface?
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### Nm of force required to keep a vehicle in motion in final gear at low rpm [closed]

A vehicle of weight 3439lbs is attempting to maintain a constant velocity of 70km/h on a flat, sealed road. The vehicle has a drag coefficient of 0.33 and cross sectional friction area of 0.65m². Air ...
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### Question involving kinematics, frictional coefficients and trigonometry [closed]

Question: A penguin slides at a constant velocity of 1.52ms-1 down an icy incline. The incline slopes above the horizontal at an angle of 6.3°. At the bottom of the incline, the penguin slides onto a ...
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### A question regarding Physics of sand-boarding

I was playing a game when I started thinking about this problem: Say, a person is sandboarding down a hill/dune, right before the slope begins, what are the conditions that must be met in order for ...
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### Static or dynamic? [closed]

Long time ago, I found a question in the book Introduction to Classical Mechanics-David Morin. The question was Sliding sideways on a plane: A block is placed on a plane inclined at an angle $\theta$....
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### Why do rotating bodies have friction between when the surface is accelerating?

For a body rolling with a constant velocity, there is no friction between the surface and lowermost point of the body, as there is no reletive velocity between the body and the ground when it is ...
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### Work done by friction on a sphere sliding down the inclined plane [closed]

If a sphere slides down from rest on an inclined plane of hypotenuse $L$ and height $H$ : Work done by friction is converted into rolling kinetic energy and as well as heat energy. If $f$ is the ...
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### Minimum coefficient of the static friction of a pencil rolling on an inclined plane [closed]

A standard six-sided pencil is placed on a notebook as shown. Find the minimum coefficient of static friction $\mu_s$ such that, if the upper cover is raised, the pencil rolls down the incline rather ...
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### Trouble in understanding why tension force is variable here?

I have trouble here understanding why the tension comes in range my teacher said that it is due to the instantaneous rearrangement of the block like if we place the the 10 kg block and apply maximum ...
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### Type of friction on circular road [duplicate]

Why is the friction static while driving a car (at constant speed) on a horizontal circular road? Please explain in details.
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### How is the acceleration of all the blocks same in this problem? [closed]

In solution of this problem the acceleration of all the blocks is taken same as $a$ . But won't the acceleration of Block $A$ and $B$ be different and the acceleration of Block $C$ would be the sum of ...
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### Why can't energy conservation nor momentum conservation be used to solve this problem? [closed]

A block of mass m is launched op an incline with speed $u$ on a rough incline. If it reaches the top find the minimum value of $u$. (slant height $l$) Ans- $u=\sqrt{2gl(\sin \theta+\mu \cos \theta)}$ ...
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### Static or kinetic friction? [closed]

Suppose i have a man standing on a plank.There exists friction between the plank and the man but there isn’t any friction between the plank and the ground. If the man starts running on the plank ...
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### How does friction stop a car?

I'm unable to understand how friction causes motion in cars and also is responsible for stopping them. When it starts the impending motion of tyres is in the backward direction that's why friction is ...
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### Is the work done by gravity equal to the work done against friction?

If there is a block on a ramp, and it slides to the bottom (with friction), then is the work done by gravity always equal to the work done against friction?
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### Why does the string of a simple pendulum need to be perfectly flexible?

The book says: "The string should be perfectly flexible, if we like to neglect the effects of different velocities of the different parts of the string during the oscillation." Can anyone ...
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### Direction of friction of a rotating ring/disk

I'm trying to understand friction but I'm getting a bit confused... If I have a ring rotating on the ground around its COM what is the direction of the friction? If I have the same ring, but this time ...
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### If I move a negative charge towards positive one on a rough surface then where does its potential energy go?

Suppose I have a positive charge and a negative charge at a distance on a rough table. The friction of the table overcomes the electrostatic force between them. So, they are stationary. Now, I push ...
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### Stacked bodies, no applied forces, internal forces accelerate the whole system [closed]

A block P of mass $m_{1}$ in on a frictionless horizontal plane and a block Q of mass $m_{2}$ is always on top of P. Initially P and Q are at rest. At time t=0, an initial speed $v_{0}$ is given to P ...
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### Why do flat-plate friction studies only consider half the plate?

I'm trying to learn friction (only - nothing else - just skin friction) on a surface as it moves through water. I'm hoping to find a working formula, including all necessary units, in terms of wetted ...
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### Work-energy theorem and the frictional force

During my attempt of fully grasping the work energy theorem, I came across this written in my textbook: The frictional force, which we represented as a constant force is in reality quite complicated, ...
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### Pressing a mass against a spring on a table with friction

Suppose I have a mass $m$ kept on a horizontal table with coefficients of friction $\mu_{s}$ (static) and $\mu_{k}$ (dynamic/kinetic). And suppose I have a spring with spring constant $k$ which is ...
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### Is friction different when viewed from a non-inertial frame?

I encountered this diagram when reading an explanation about why the front wheels of cars lift up when they accelerate. The diagram is in the reference frame of the car, so that there is a fictitious ...
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### In which direction will the friction act?

Suppose a block of mass $1$ kg is kept on a rough horizontal surface. Let the friction coefficient be $0.2$. Now let's say, I apply a force of $1$N in the east direction. Friction will act in the ...
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### Why does a bike skids on the sand?

Whats the theory behind bike skidding on the sand? Is it related to friction and if then why it skids. Is that the sand has more friction if so then pedaling should be difficult rather than skidding.
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### What forces are there against the motion of walking or running?

When we walk or run, are there any forces that counteract the static friction between our feet and the ground? I can’t seem to think of any, but if not, why is it that we still need to push on the ...
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### The curl of a friction force being zero

Consider the resistive force modelled by the function $\vec{F} = -b\vec{v}(t)$. The curl of this function, $\nabla \times \vec{F}$, is [\frac{\partial}{\partial y} (\frac{dz}{dt}) - \frac{\partial}{\...
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### Moving with constant velocity in presence of net force

If I neglect air resistance is it possible that I can walk with constant velocity? Suppose that I take equal steps of equal length every second and therefore my velocity doesn't change. That means ...
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### Calculate the acceleration of a superman in running shoes [closed]

The friction coefficient between an athlete's shoes and the ground is $0.90$. Suppose a superman wears these shoes and races for $50 m$. There is no upper limit on his capacity of running at high ...
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### Worked Example - Classical Mechanics by David Morin

Problem: A rope wraps an angle θ around a pole. You grab one end and pull with a tension $T_0$ . The other end is attached to a large object, say, a boat. If the coefficient of static friction ...
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### Physics of a coin on a turn table

Suppose a coin is placed on a turn table which is then rotated. The coin initially rotates along with the disk and may fly off eventually. My question is, why is static friction acting radially inward ...
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### Why does the glass move?

I have observed at my home that when there is a small puddle of water on a glass table and an inverted steel glass is kept on that puddle of water, the glass starts moving on its own after some time. ...
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### Work of friction on rolling objects

In many cases when there is friction acting on a body which is rolling without slipping ( for eg : a body rolling down a inclined plane ), We say, that the work done by the friction is zero as the ...
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### What happens with diamond on atomic scale when we simply touch it?

We all know that diamond has very strong covalent bonds that require a lot of energy to break. We can destroy it by burning it, but what happens when we touch or rub it with a soft material? How long ...
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### Torque on a block on an inclined plane

When a block is stationary on an inclined plane, the frictional force on the base of the block has a torque about the center of gravity of the block. However, the block does not rotate. Which force ...
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### Objects rolling down inclined plane at different speeds

Consider the case of objects rolling down an inclined plane at different speeds depending on their moment of inertia. Some basic equations are shown in this screenshot from Michel van Biezen. He is ...
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### Why can't we take the surface as part of a system when conserving linear momentum?

In a problem I'm facing, friction acts on the system that I wish to apply conservation of linear momentum. Why can't I take the surface as a part of system and conserve momentum? As the surface is ...
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### Are objects at high speeds subject to friction (in described fashion)?

https://www.youtube.com/watch?v=1NnyVc8r2SM In this video quicksilver moves plastic bullet's with his finger from a different time reference. Needless to say, if bullets were in contact with an ...
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### Where does the equivalent friction act on a block sliding on an incline?

If a block is sliding down an incline it means the Normal force is acting at a point $x$ distance from the middle of the bottom of the base to produce an anti-torque to keep the body in rotational ...
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### What lies between “perfectly smooth” and “perfectly rough”?

In elastic collisions of spheres, there are two approximations that can be made: Either they are perfectly smooth, and you ignore the rotation component, or they are perfectly rough and the rotation ...
I am confused on a trivial problem here involving Newton's 3rd Law and the FBD of the following problem, where the question asks for the differential equation of motion, with $V_2$ as output and \$...