# Questions tagged [friction]

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

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### If you had two “perfectly” flat surfaces of the same material?

Let's say you had 2 nano-engineered surfaces of diamond which were as 'flat' as possible (of course considering the radii of each carbon atom in the lattice)... would there be any friction between ...
66 views

### Work done by friction wrong in general physics [closed]

Though some general physics textbooks say that work done by friction isn't straightforward, many textbooks still calculate it as if it were a work done by a usual force, even without declaring that ...
438 views

### Motion of a car on a banked road

I have read about the motion of a car on a banked road. I read that the maximum possible speed of a car on a banked road is greater than that on a flat road. I know the formula for finding velocity ...
27 views

### Does kinetic friction increase a body’s acceleration once the body starts moving?

Let’s say there is a block of mass $1$ kg resting on a surface. I studied in my textbook that coefficient of static friction is usually greater than the coefficient of kinetic friction for a given ...
51 views

### “A spinning top spins much longer because it experiences less frictional torque” is wrong? [closed]

The above quote was found in my physics textbook, but it struck me as strange because my understanding of friction is that the surface area doesn't matter in calculating the amount of frictional force....
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### Why does frictional force depend on normal reaction and not the weight of a body?

One possible explanation I came across for this was that if you have an external force and you press on the body, the body's frictional resistance to motion increases and hence it should depend on ...
335 views

### About the fluid friction along the wall in pipes

I wonder how can the friction between a fluid and a wall in a cylindrical pipe can be calculated. Is there any theory that I can refer to? I also want to check if there's any relation between the ...
291 views

### Can the work by static friction on an object be negative?

We know that static friction acts between two surfaces in contact when they are not moving relative to each other (and when some other force is trying to move one object over the other). This question ...
45 views

### Clarification on friction coefficient for a mass rolling down an incline [closed]

I have been working on the following AP Physics 1 free-response question: 1974M2. The moment of inertia of a uniform solid sphere (mass $M$, radius $R$) is $\frac{2}{5}MR^2$. The sphere is ...
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### Where will the energy go into when the block is at rest in the presence of friction?

Suppose a block is being accelerated on a horizontal plane by a machine in the presence of friction. The machine will burn fuel and generate energy which will be used in accelerating the block and ...
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### PTFE on liquid mercury friction coefficient

Are there any studies or research been done where I could see what is the coefficient of friction on a PTFE plastic sliding on a liquid mercury base? I found that the friction coefficient for PTFE is ...
1k views

### Thermodynamics and Newton's second law

Is it correct to say, that the Newton's laws (or a Newtonian system) is reversible if the friction isn't considered (the fact that the time is of second order $\frac{d^2x}{dt^2}$) and an isolated ...
29 views

### Would the weight of an object increase if the pressure of the surrounding is increased? [closed]

I'm thinking something like if I take a box and place a weighing machine and an object inside it...then if i increase the pressure inside that box would i observe any change the weight of the object? ...
241 views

### Isn't friction on an incline coefficient of friction times the Reactional force?

Question - "As shown in figure a body of mass 1 kg is shifted from A to D on inclined planes by applying a force slowly such that the block is always in contact with the plane surfaces. ...
178 views

### Role of friction during Collisions

Normally, in questions of collisions, we tend to apply conservation of momentum (and in cases of elastic collisions, conservation of energy as well) and we usually ignore the frictional force acting. ...
2k views

### Damping coefficient and damping ratio [duplicate]

I am not sure if I understand the term damping coefficient correctly (I am a high-school student). Here's the link for the info that I learned: http://hyperphysics.phy-astr.gsu.edu/hbase/oscda.html ...
135 views

### What does the term “no slipping” mean in mechanics?

Say, I have two blocks. One block is on top of the other. Suppose friction is present everywhere. What is the condition for no slipping?
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### Resistive forces on Simple Harmonic motion

How is a simple harmonic motion affected by resistive forces? In this case, a spring block system is placed on rough horizontal surface. How to derive the block's displacement equation? I couldn't ...
69 views

### Why is the Normal force in the picture not perpendicular to the surface?

My teacher said that the first is true, but the normal force should be perpendicular to the surface?
5k views

### Motion of a box in a conveyor belt

When a box is dropped in a conveyor belt moving with a constant velocity to the right, the box exerts a friction on the belt to the left. In response to it the belt exerts a friction on the box to the ...
70 views

### Where does normal force shift to?

"A block of side length $a$ and mass $m$ resting on a ground with a coefficient of friction $\mu$. A force $F$ is applied on the upper edge of the block (think of the cross-section and one of the ...
149 views

### Vertical component of friction

If we have a car of mass $m$ sliding around a banked curve of angle $\phi$ with some coefficent of friction ${\mu}$, then the normal force will be $$Ncos\phi= mg + {\mu}F_{g}\sin\phi$$ But this ...
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### Why friction is attractive force whereas normal reaction is repulsive?

Both friction and normal reactions are contact forces. And according to what my textbook states both are of electromagnetic in origin. If so why normal reaction, say a block on a table pushes it away ...
36 views

### Confusion regarding the direction of static friction and point of contact

I'm doing a practice question for my Physics 1 class, and after solving this I believe the answer key is incorrect. However, I'd like to confirm this and make sure I'm not incorrectly deciding upon ...
145 views

### Doubt relating pure rolling

As we know, when an object perform pure rolling on a plane having friction the friction acts on the edge in the direction opposite to the direction of its translational motion. There are no other ...
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### Block on a horizontal surface being pushed against a wall

Here is the problem. A block (box) of a mass $M$ being pushed along a floor by a constant force of $F_\text{push}$. Both the static $\mu_s$ and kinetic ($\mu_k$) friction coefficients are given. I ...
146 views

### Unclear things about conservation of energy

I have started reading Feynman Lectures in Physics, First Volume, with absolutely no background in physics [*]. In the fourth chapter, conservation of energy, I am having difficulty understanding ...
517 views

### Why does a book leaned up against a wall sometimes fall over after being stable for many hours?

This problem has been vexing me for years. Sometimes, you lean a book up against a wall and it stays there (the static frictional force balancing gravity, etc), but then after a long time (hours or ...
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### Cars' wear resistance, quietness and water drainage dependence on thread pattern on tires?

Why can tires with fine thread patterns increase cars' wear resistance, quietness and water drainage? What is the logic behind? The following is the tire ad I saw: Nowadays, under the premise of ...
35 views

### Free Form Diagram of one block on top of another block [duplicate]

I am having understanding the soln to this problem. Here, FDM of Block A and Block B is drawn separately to split the problem. Now in Block B, i fail to understand why does N1 considered act ...
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### Physical interpretation of time constancy in damped harmonic oscillator

I know that one can mathematically derive and prove that in a damped oscillator (without external driving) the time period of oscillations is a constant. But how can one physically interpret as to why ...
151 views

### Why can't $U=b\mathbf{v} \cdot \mathbf{r}$ be considered a potential for the drag force ${\bf F}=-b {\bf v}$?

Consider the function $U(\mathbf{r},\dot{\mathbf{r}})=b\mathbf{r} \cdot \mathbf{v}=bx\dot{x}+by\dot{y}+bz\dot{z}$, where $b$ is the drag coefficient. Why can't this be considered as a potential energy ...
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### Why is the answer different with energy conservation vs forces?

Q) An insect crawls up a hemispherical surface very slowly.The coeffiecient of friction is $\mu$ between surface and insect.If line joining the centre of hemispherical surface to the insect makes an ...
6k views

### Can there be friction unless the objects in contact are not acted upon by an external force?

The definition of friction I read from The book, General Physics written by Henry Crew is that, The resistance which either one of the body offers to the motion is called force of friction". If it is ...
120 views

### Sliding to Rolling

In a problem where a sphere is initially sliding and then begins to roll after having travelled some distance. The thing that confused me is that the work done by friction on the sphere is not simply ...
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### Basic question on friction

Consider the whole system initially at rest.Suppose there is friction between the blocks, but not between the lower block and the floor. Suppose I apply a Force F to the left over M, with F greater ...
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### Is kinetic friction opposite to the velocity even in circular motion? [closed]

Is kinetic friction opposite to the velocity even in circular motion?
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### The role of friction in rolling without slipping

I am confused about this whole subject. Let's suppose we have a disk standing still upon the ground. Now let's say someone inside the disk shoots a projectile to the left. From momentum conservation ...
753 views

### Is kinetic friction still constant at the transition from static to kinetic friction?

I'm looking at this graph from here: The answer providing the above graph explains how kinetic friction is constant. However, the graph tells me that after static friction is overcome, there is a ...
186 views

### Why does limiting friction have to act when a block tied to a wall is pulled?

A block lying on a rough surface, is connected to a wall by a mass less, inextensible string and an unknown amount of force is applied to the block opposite to the side of the wall. Now, if it is ...
188 views

### When you have engine at idle and turn your car, where does the kinetic energy go?

When you turn the front wheels to the right for example, your car will tend to continue in its original forward direction. However, there is friction between the wheel and the ground that prevents it ...
78 views

### Explaining why rubbing two surfaces together by hand create convex and concave shapes?

From this video (relevant timestamp included in URL): https://www.youtube.com/watch?time_continue=768&v=ABRysNzcdvw&feature=emb_title It shows how rubbing two surfaces together by hand with ...
235 views

### Is the “efficiency” of car brake affected by how much force is applied by the brake?

Someone argues with me that stepping on a car's brakes for long periods of time will wear out the brakes faster than applying the brakes for short periods of time. We were talking about stepping on ...
1k views

### Conservation of energy of 2 identical Rolling Disks with and without friction

My physics book claims that if two identical disks moving at the same velocity travel up nearly identical hills, with the second hill not having friction, then the disk rolling up the first hill will ...
39 views

### Rotational motion with friction

I am quoting this question from IE Irodov Dynamics of solid body q 248. A uniform cylinder of radius R is spinned about its axis to the angular velocity Wo and then placed into a corner. The ...
233 views

### Confusion about work done by a force in different reference frames

Suppose I have a little mass m resting on a big slab mass M resting on a table. There is a frictional force between the little mass and the slab, but not between the slab and the table. Suppose I now ...
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### Normal force and Electrostatic Force [duplicate]

My book, in mechanics, claimed that the normal forces were actually a result of electromagnetic force and that the "hand of the strongest weightlifter will crumble under the weight of a feather" if ...
347 views

### Work done against a force

Consider a body of $1\ \rm kg$ mass at rest at ground. Now as we know, it can be lifted by a force equal to its weight. So we have to apply a little bit more force then its weight. let \$g= 10\ \rm ms^{...