# Questions tagged [contact-mechanics]

To be used when the question involves contact forces acting on one/many body systems and accompanying dynamical changes. For general questions,use [mechanics] and for contact mechanics based questions,use [contact-mechanics]

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### Can the nature of Normal Reaction be predicted beforehand for any mechanical set-up?

Is it true that it is possible to predict the nature of Normal Reaction ( magnitude, direction, etc. ) in any mechanical set-up without first solving the dynamical equations of motion and constraints? ...
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### Conceptual doubt related to normal force in a two-block system kept on frictionless surface

I was solving this question in which we had to calculate the normal force between blocks $m_1$ and $m_2$ Here, two blocks of mass $m_1$ and $m_2$ are in contact on a frictionless surface, and a force ...
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### How can Hertzian mechanics possibly give different solutions for static and dynamic particle contact?

I am trying to understand a case of impact between a sphere and a half-space. Suppose I have a particle resting on the half-space in the gravity. The penetration depth $\delta_{max}$ of resting ...
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### Elevator force diagram

Am i correct when i say that all the seperate bodies and the whole system has to have 10m/s² acceleration? So can i say : F=ma For elevator : (T-R) = 10 × mass of elevator For box : (R - 20N) = 10 × 2 ...
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### Do contact forces form a field/wave?

Non-contact forces like gravitational forces exist between two objects in any medium because of the establishment of a field/wave. Since at an atomic level, 'physical' contact won't really be possible ...
• 115
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### Are contact forces exerted due to gravity

For example, a book rests upon a table, on earth the weight of the object is balanced by the normal reaction force exerted by the table on the book but in reality, the normal contact isn't the ...
45 views

### Direction of undetermined contact force & undetermined Normal force [closed]

I am not getting the following sattements related to contact force and normal force which are: If the direction of contact force cannot be determined, it should be shown as two components. If ...
64 views

### How do I analyze the cue tip at impact with a billiard ball?

this is not a homework problem, it is something I've been trying to understand in billiard physics (because I'm a big pool fan) When we hit the cue ball off-center to impart spin, we still don't know ...
54 views

### Friction force on a cuboidal block for different orientations - how does $\mu$ change with orientation? [duplicate]

It's been a long time since I did problems on friction but here's one... Consider a cuboidal block of dimensions 123 meters with a total mass of 1 kg. There are 3 cases that we need to look at: Its ...
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### If there is no gravitational force on the earth (i.e. acceleration due to gravity is 0m/s^2), will bodies in contact still experience a normal force?

My question arises from this post by Ashish Arora, where he asks: "If $g$ becomes zero suddenly, a body at rest on a fixed table will start moving away from it." In the above question $g$ is ...
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1 vote
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### Using Hertzian contact mechanics to explain fracture cones when an elastic sphere is pressed onto an elastic half space

I'm trying to understand the Hertzian cone fracture process from a continuum mechanics point of view. I'm considering a problem where an elastic sphere is pressed quasi-statically onto an elastic semi-...
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### Why do we always assume in problems that if things are initially in contact with each other then they would be like that always?

I am a high school student and I am confused in one thing:"Why do we always assume in problems that if things are initially in contact with each other then they would be like that always?" 1)...
563 views

### How to obtain the equivalent Young Modulus in Hertzian contact?

I would like to understand why there's a $\nu²$ in the expression of the equivalent Young modulus in the Hertzian contact theory. Here's a common expression for an elastic sphere crushed on a rigid ...
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### Controversial model of microscopic springs to explain both static friction force and normal force

Many authors (like Randall D. Knight and Eric Mazur) explain nature of static friction force (either static or kinetic) in terms of molecular bonds, which are developed on microscopic bump of ...
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1 vote
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### When solving problems on linear momentum, when can external forces be neglected?

I was recently solving a problem in which one end of a massless string (in vertical orientation) was tied to a block of mass $2m$ and the other end to a ring of mass $m$, which was free to move along ...
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### Any material for learning Computational Contact Mechanics?

I am currently studying computational contact mechanics for my research. Does anyone know some good material (especially introductory material) for this subject? I have already read the following two ...
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### What is the difference between normal and contact forces?

What is the difference between normal and contact forces? Isn't the contact force exactly equal to the normal force? I don't see how some contact forces aren't perpendicular to the object they are ...
423 views

### Understanding the interactions resulting from the effect of a force on an object that is in contact with another object

I've tried to think on how a force acting on a single object that is in contact with another makes the system of the two accelerate and wanted to know if I'm thinking correct. Consider the situation: ...
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### Distribution of normal force of a lever system [closed]

So from the diagram, there is a rigid solid subjected to a downward applied point force on its rightmost end, and a fixed pivot on its leftmost end. The rigid solid A is in contact with an elastic ...
152 views

### How no Contact forces on objects with stacked on top of each other

How can there be no contact force between two bodies stack one top of another during freefall if they are in contact?ho
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### Free fall and contact force

If two bodies are stacked on on top of other and in free fall and there is no contact force how come they remain in contact ignoring drag. Secondly if two object were at rest say on table and table is ...
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### How many derivatives for the position of an object?

Here is a thought experiment. I have two steel balls on a steel surface. One is stationary at $(0, 0)$. The other is rolling towards it along the $x$-axis from the negative side. It will collide ...
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### Is contact force repulsive or attractive?

Here I'm talking about the contact force when, say an object in placed on the surface of, maybe a table. I understand attractive and repulsive forces operate between the object and the table. Here is ...
1 vote
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### What exactly causes the normal force and how is it related to friction? [duplicate]

So I've read many answers on the internet and have not yet come to understand the origin of the normal force. What I've to come to understand about the normal force, is that it is the electromagnetic ...
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### Deformation and Adhesion with Particle Contact Time During Impact

Let's say I have a spherical particle impacting a large flat target (let's say it's a half space) at high velocity. It seems I can approximate contact time during impact by dividing impact velocity ...
608 views

### When a force is applied continuously on a two-body system such that both of them touch each other why do they move with same acceleration?

If we take two objects such that both of them are in contact, then a force is continuously applied on any of the object both of them will move with a constant and equal acceleration.Why does that ...
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### Kleppner problem 6.33 Confusion [closed]

A cone of height $h$ and base radius $R$ is free to rotate around a fixed vertical axis. It has a thin groove cut in its surface. The cone is set rotating freely with angular speed $ω_0$, and a small ...
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### Physics of "force spreading" on impact on a surface

Consider a plate $P$ of thickness $d$ (for example a plate of wood) laying on a hard surface $S$ (for example on concrete floor). Suppose you have a maximum value of pressure $p_{\mathrm{max}}$ $S$ ...
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1 vote
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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 ...
438 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 ...
122 views

### What is weight at the particle level? How EXACTLY do atoms exert weight on each other?

This is what my intuition says about how the concept of weight works in a solid. The light brown arrows are the vectors of gravitational force, the light gray parts are the electron clouds around ...
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### Contact pressure - rope on pulley

I've been trying to find a way to calculate the contact pressure between a rope under tension and a pulley (free to move, or fixed). I'm expecting to find an equation that considers the wrap angle - ...
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### How do I include friction due to normal force in Lagrange Equations?

I am going through the Goldstein book on classical mechanics and the after he derived the Lagrange equations he used Rayleigh dissipation function to include friction as a generalized force. In school ...
1 vote
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### Doubt on contact force being described as a electromagnetic force at molecular level

Contact forces are forces that come into play only when two objects come in contact with each other. In this wikipedia article, it is written that Molecular and quantum physics show that the ...
365 views

### Deformation of an elastic ball

Suppose a free sponge ball is being compressed, due to applying a known force in a specific direction. The ball's shape will be distorted. Given are the direction of the applied force, as well as its ...
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### Strange sound of low frequency produced from 2 steel balls

When two steel balls collide, or any metal objects collide, a high frequency sound is produced. However, what was strange is that when I held two metal balls in my hand, and moved them around, it ...
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### Calculating the pressure between a housing and a shaft in an interference fit

I'm trying to calculate the pressure between a journal/shaft and a housing bore in a case of interference fit. Considere a 2D axisymmetric (effectively 1D) journal bearing with interference fit: ...
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### 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 ...
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### Total force generated in a pneumatic cylinder-piston with known gap size

Assuming that we have a pneumatic cylinder-piston with arbitrary but known surface area A, a known clarence c, and a known length L. What is the best model to describe the total steady-state force ...
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