# Questions tagged [friction]

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

206 questions with no upvoted or accepted answers
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### What is the specific source(s) of sliding kinetic friction

In simplistic (K-8) physics classes, it seems to be generally instructed that the friction between two moving surfaces is due to the unevenness of each surface and the microscopic roughness. However, ...
0answers
446 views

### Why does the overhand knot jam but the figure-8 knot doesn't?

After tensioning a rope with an overhand knot in it, it is often very hard if not impossible to untie it; a figure-8 knot, on the other hand, still releases easily. Why is that so? Most "knot and ...
1answer
124 views

### What would be the optimal diameter of gold grains if you want to fill a pool with them and swim in it?

I was wondering, if I were to fill a pool with gold/gold dust, what would be the optimal diameter of the grains to minimalize the friction to a point at which you would be able to swim in it ((and if ...
1answer
93 views

### Drifting vs. rolling when starting race

Imagine you are about to start a car race. You are on the grid, waiting for the green light. What should you do in order to optimize your start? Some people would say that a drift start would be the ...
1answer
141 views

### How are two objects heated by friction?

Let’s say that we have two objects made of different materials, both at room temperature. Surfaces of the objects are rubbed together, producing frictional heat. Is the heat distributed evenly, i.e. ...
0answers
26 views

### Transition from damping to runaway in non-Markovian friction

I am studying the dynamics of a particle with history-dependent friction. That is, the particle velocity $v(t)$ is governed by $$\frac{d v}{dt} = -\int_0^t M(s)\, v(t-s) \,ds ,$$ where $M$ is the ...
1answer
35 views

### Problem regarding friction

I require a clarification on some steps in the solution of the following problem. Problem: The coefficient of static friction between two blocks shown in figure is μ and the table is smooth.What ...
1answer
56 views

### Explain why the magnets move towards eachother in this setup

I have two bar magnets (actually stacks of small magnets, but I believe they should behave the same) attached to a stack of (presumably conductive) coins, and not diametrically opposite. When I ...
3answers
164 views

### 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 ...
1answer
56 views

### What would the ideal amount of gravity be for an Olympic sprinter?

The goal here is to get the sprinter running as fast as possible. How much of an effect would more or less gravity have on the top speed of an Olympic sprinter, say... Usain Bolt? 6 ft 5 in (1.95m) ...
4answers
1k views

### In which direction does the friction act in a circular motion?

I want to know how a body moves on a circular track. Suppose a car enters a circular path. If I don't turn my steering wheel, then the car would travel in straight line and perpendicular to the radius ...
0answers
62 views

### Physical origin of gradient-like system with nonautonomous damping term

I am in mathematics major, and I am considering the equation $$\ddot u(t) + \gamma(t) \dot u(t) + \nabla \phi (u(t)) = g(t),$$ where $\phi: \mathbb{R}^n \to \mathbb{R}$ is of class $C^1$, convex and ...
1answer
583 views

### Circular motion, kinetic friction and tension

Hi: I've read this post: Uniform Circular Motion w/ Tension and Friction and helped me a lot. I have a similar problem: At one end of the rope ($R = 1 m$) is tied a mass ($m = 3 kg$) and the ...
1answer
926 views

### Damping coefficient and damping ratio

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 ...
3answers
669 views

### Dissipation and first law of thermodynamics

Consider the following situation: a certain gas is contained in a well-insulated cylinder with a well-insulated piston head. Now, in this case the piston is not frictionless. In order for the piston ...
1answer
222 views

### Is it possible to eliminate Van der Waals interactions?

I came to know that the friction force actually depends on the surface contact area due to weak interactions (adhesion due to Van der Waals forces) between the atoms of both materials increasing in ...
0answers
41 views

### How does friction cause a spinning top to fall?

I am wondering how friction can create a torque to change the angular momentum and cause a spinning top to tilt, like in the diagram of a close up of the rounded tip of a top while the angular ...
1answer
51 views

### Is friction an emergent phenomenon?

The microscopic origin of the frictional forces is due to contact between irregularities of the surfaces as seen here . Electromagnetic interactions are the fundamental forces responsible for ...
0answers
36 views

### How does different shuffleboard powder affect the disks' speed

I do know there is friction and surface tension involved here but am not sure on how exactly does different kinds of shuffleboard powder affect the disks' speed. So taking into the account the ...
2answers
75 views

### Being Frictionless, surface of contact

I hear frequently references to a smooth surface, or frictionless pulley. Can being frictionless be obtained if only one of the 2 surfaces has 0 coefficient of friction? Or it is for the contact of ...
0answers
45 views

### Deriving equations of motion using Lagrangian formalism for inverted pendulum on a cart with friction between pendulum and pin

I know this is a problem with plenty of examples and solutions but I can't find one where the friction between pendulum and pin (I know it's negligible) is taken into account. My main question is if ...
0answers
263 views

### what is the relation between friction, clearance/tolerance, roughness and mechanical properties in a prismatic joint?

Consider an axisymmetric model of a prismatic joint: Assumptions: The circular shaft moves linearly, only in longitudinal/axial direction The shaft has a diameter of $D$ The clearance between ...
0answers
99 views

### Minimizing mechanical energy subject to fixed angular momentum

I may be in error, but this problem (ch. 4, no. 14 on p. 203), from Symon's Mechanics, 3rd edition, seems wrong to me: A mass $m$ of gas and debris surrounds a star of mass $M$. The radius of the ...
2answers
66 views

### Experiment on friction coefficient

Here you can see the results of the experiment about a friction coefficient: The mean of the friction coefficient becomes 0.262 but when I do a linear regression in the form of y=mx the slope is 0.31....
0answers
270 views

### Extension of the Capstan Equation

The Capstan Equation relates the holding force and the load force for a string wrapped around a cylinder. However, most people who work with heavy machinery know that if you wrap a rope around a post ...
1answer
138 views

### Effect of forces inside a sphere

What would be the effect of applying two parallel forces of the same value at opposite points of the equator inside a sphere? Common sense tells me that it wouldn't move, but it seems that it could ...
0answers
150 views

### What IS the precise angle of repose of Cadbury Creme Eggs, anyways?

So, in What If, made by xkcd guy Randall Munroe, an off-handed joke about his famous love of Cadbury Creme Eggs was made. In the image's mouseover text, Randall jokes his life's dream is to own ...
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183 views

### Lagrangian Mechanics + Account for friction of block

$\newcommand{\dd}{\mathrm{d}}$ I am trying to work out the Lagrangian mechanics for a pendulum problem in order to animate it. I'm working on one of the examples in the Wikipedia page on Lagrangian ...
0answers
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### Coulomb's static friction in multidimensional case - decide which mass begins to move

Consider a system of N coupled oscillators, under the effect of elastic forces, damping, dynamic and static friction and an external force; for simplicity, let's suppose $N=3$. The friction model is ...
3answers
986 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 ...
0answers
1k views

### Can iron filings on a magnet be removed using a stronger magnet?

After some experiments, I had some NdFeB permanent magnets "contaminated" with iron filings, sticking to it's poles surfaces/edges - you may have seen that before. There are some working ways to ...
0answers
152 views

### Friction of an object falling between two walls

I'm simplifying this problem into 2D for easier understanding. Lets say we have 2 vertical walls separated by distance x. Inside these walls I place an object that is only slightly smaller than x in ...
1answer
2k views

### Why friction force is force of constraint?

My understanding about constraint force is that it is a force which limits the geometry of particle's motion. For example, situations such as the particle trapped in a track or limited in domain can ...
0answers
216 views

### Is there any place you can safely skydive without a parachute?

While trying to explain to someone how a kitten walked away from a fall from a skyscraper I got to wondering if there's any place a human could do that and I find myself out of my depth. The only ...
0answers
576 views

### Why did increasing the Ackermann geometry in my race car make it faster in corners?

Ackermann geometry is used to account for the different radius arcs that the front tires follow when the steering wheel is turned from center. It's often expressed as a percentage: e.g. 25% Ackermann, ...
1answer
39 views

### Work done by friction on an inclined plane

A rough inclined plane is placed on a cart moving with a constant velocity u on horizontal ground. A block of mass M rests on the incline. Is any work done by force of friction between the block and ...
0answers
33 views

### Is it possible to model a locomotive capable of going 0-60 in 60 secs with $\sum F=F_{engine}+\mu_{rolling}mgv$?

The problem of just considering engine force and rolling friction $$\sum F=ma=F_{engine}+\mu_{rolling}mgv$$ is that when you solve for velocity like $$\dot v=\frac Fm-\mu gv$$ with initial ...
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39 views

### Friction at high speeds

I am reading a book which mentions that frictional force is not exactly proportional to the normal force at high speeds. Quoting: Once the bodies slip on each other frictional force is, $kN$. This ...
0answers
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### In Feynman lecture vol1，chapter12 friction between two wet glasses, is there any atmospheric pressure related during the process?

In Feynman lecture vol1，chapter12 friction between two wet glasses, is there any atmospheric pressure related during the process? Does the water between two glasses make use of atmosphere pressure? Or ...
1answer
29 views

### Calculate the kinetic friction velocity vector from the kinetic friction force in a simulation

I am doing (programming) a simple kinematic 2D simulation on blocks. The idea is that the block will have a force applied. 1) From the force and mass I calculate the the acceleration vector (will ...
1answer
26 views

### Calculating Rolling Friction in a Lab

What would I have to measure to determine the rolling friction of a model car? Currently, I have the horizontal pulling force that the lab procedure calls for on the car, and enough data to make a ...
0answers
42 views

### Turbulent flow in a pipe - how to compute the friction coefficient $\lambda$

Consider a pipe of diameter $D = 0.01$ m and Length $L = 1.0$ m represented in the figure underneath. At the in- and outlet, the pipe cross-section converges, respectively diverges smoothly. We will ...
1answer
24 views

### Is there a reference frame in which the static friction from rolling does positive work?

I am worried this will be deleted as a duplicate question, so I will try to be extra clear what I am asking: In some reference frames, static friction can do positive work. If you have a crate in the ...
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### How to calculate drag caused by string?

An example - I throw a tennis ball with a short string hanging off one side. As the ball flies the string is dragged to the side opposite the direction of the ball's velocity vector, anchoring the ...
1answer
66 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 ...