# Questions tagged [statics]

Analysis of a system of bodies where all forces are in balance and there is no motion relative to a chosen reference frame.

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### What is a solution for the problem (Statics, connections and reactions)? [closed]

In image below: q_1 = 6 a = 4 b = 5 c = 3 P_1 = 7 m - ? So I need to find m? Please help
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### Relationship between net torque and net force in constrained systems

If the movement of the rigid body is "constrained", let's say a ladder leaning against a wall, would net torque $= 0$ always imply net force $= 0$? In most physics questions, torque and ...
1 vote
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### Is torque possible without any pivot point?

In the picture, AB is a rod. The resultant of force P=10N and Q=5N works at point C which is P+Q. When I apply both forces simultaneously, the rod will rotate and accelerate. 5N from both end will ...
1 vote
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### If two oppositely charged rods are placed near small pieces of paper why do they both attract the paper?

Take two oppositely charged rods, place them near small pieces of paper, and both rods will attract the paper. Why do both negatively and positively charged rods attract the paper in the same way?
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### Simple statics: force due to pressure and tension in an equilateral triangle

A rope encloses a compressed two-dimensional gas with pressure $p$. First suppose the gas is constrained to be square (e.g. it's in a square container that can shrink and expand). Let $T_1$ be the ...
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### How to solve this static mechanics problem? [closed]

I'm trying to recall how to solve some simple static mechanics problems, and found one on youtube that was solved in a way but I remember solving it in another way (more or less it is the same, but I'...
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### How to find Shear Force and Bending Moment in Finite Element Method for a cantilever beam with many elements

I have a cantilever beam with lots of elements. I am trying to find the sheer force and bending moment diagrams of the beam. EVERY SINGLE TUTORIAL AND EXAMPLE I SAW ONLINE SHOWS HOW TO DO IT FOR A ...
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### Moment and forces in joints

Can anyone help me understand the significance of the forces in joints? My method: Let FG be tension T, force at D be D parallel to y-axis, force at B be B parallel to y axis Taking moment about B ...
1 vote
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### Maximum acceleration without tipping over - torque balance analysis on an non inertial reference system

edit: This is not a homework question, but a question about whether choosing a different rotation axis can affect the torque balance analysis. I am just using the following example to illustrate ...
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1 vote
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### Catenary curved string with differing linear densities - Linear density distribution

Do you guys know if there's some kind of weight distribution that fits a problem like this one? Let there be a string with two different sections with different linear densities, like the following ...
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### Nonuniform mass density per unit length - Torque

I ran into a question titled "Balancing a stick" from David Morin's Classical Mechanics book, Chapter 2, that states the following: Given a semi-infinite stick (that is, one that goes off ...
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### Which condition exactly does Newton's First Law of Motion apply?

As I was reading about Newton's First Law of Motion from some textbook, I noticed some detail that seemed to conflict with another textbook which I have read previously. Book 1 provided the following ...
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1 vote
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### Weight Distribution when lifting furniture with a partner [duplicate]

Help solving this question would be appreciated: As a short person at 5'3'' with short arms, I find it challenging to lift furniture with a taller person, because they always naturally lift the object ...
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### Morin 2.16 - Balancing a semi-infinite stick

Problem 2.16 from Morin's Classical Mechanics: Given a semi-infinite stick (one that goes off to infinity in one direction), determine how its density should depend on position so that it has the ...
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### Can a three force member be subdivided into two force members?

The question can be better understood with the help of the given example. What I can think: Member CD: a two-force member. Member DEG: Because member DEG is the largest structure among members EG, DE ...
1 vote
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### What is the correct intuition behind Varignon's Second Theorem? (See the example in the details.)

Consider, say, a rigid 2-D square sheet, of uniform mass density, initially occupying the square: $$-2 \leq x_1, \ \ x_2 \leq 2$$ in the $x_1 x_2$-plane. The plane is a frictionless table, on which ...
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### Confusion regarding calculation of amount of water in container to ensure lowest centre of mass

When I tried to calculate the volume of water that should fill a massed container such that the centre of mass of the system is the lowest, I obtained two separate results when two different methods ...
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1 vote
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### Inclined plane question: Why does $F_f = Mg \cdot \cos{\theta}$? [closed]

So I was reading Morin's Book and it had this as first example. My confusion is with the forces here, the book mentions $F_{f}=Mg(\sin(\theta)-\cos(\theta))$ and $N = Mg(\cos(\theta)+\sin(\theta))$ ...
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### Weight as tension

Tension problems are very simple, but, in some of them, there is a singular case: In this one, to get the values of the tensions, we take into account only three forces: the weight becomes another ...
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### How non-collinear forces balance each other?

In the system of parallel forces , all the forces are non-colinear. So how to they balance each other?. Here in this case a wooden plank is supported at its end by two supports. All the forces here ...
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### What curve does a rod form when bent to intersect 3 or more points?

Suppose that we have a sufficiently thin, flexible cylindrical rod of length $L$ made from a homogeneous, isotropic material, and that initially [at rest?] the central axis of the rod is a straight ...
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1 vote
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### Equilibrium and constitutive partial and algebraic equations describing stresses and deformation of an axisymmetric elastic thin shell over a hole

I want to design a vacuum table to clamp down a very thin plate and I want to know the stresses and deformations due to the atmospheric pressure. Consider the simplified model below: ...
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### How to calculate the distributed weight across multiple "scales" (points)

Intro As the title says, I'm looking for a way to calculate the weight (or even better, the percentage of weight) at multiple points on a rigid object. Long story short, I'm making a game and need to ...
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### Is It true that If the angular momentum is zero with respect to any point then the system is at rest?

If the angular momentum is zero with respect to any point, surely the system is at rest. It is intuitive that this is the case but I would like to prove it. I guess supposing the opposite leads to ...
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### Motionless chain in a tube

Good evening, I come to this site with doubts on some very basic concepts. I have started reading through Morin's Classical Mechanics. Among the problems on Chapter 2, Problem 3 says: A frictionless ...
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### Truss Deflection Problem

Dear Readers, why doesnt the deflection formula depend on moment of inertia (I) or even the second momnet of area that are responsible for the cross-sectional shape of beam. Does that mean in the ...
1 vote
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### Critical point in 2D Potts model and duality equation

I have to prove, considering the limits of high and low temperatures, duality equation:  Z=q e^{2 N K} F\left(e^{-K}\right)=q^{-N}\left(e^{K}+q-1\right)^{2 N} F\left(\frac{e^{K}-1}{e^{K}+q-1}\right) ...
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### What is the physics behind a TV wall mount? [closed]

As I was installing this wall mount, I began to wonder how exactly physics is at work with it. In other words, how does the design of the mount play a role in ensuring that the mount itself supports ...
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### Why is lever in mechanical equilibrium?

Let's consider a lever with a fulcrum (see image below), such that it's load arm and load are $d_1$ and $F_1$, respectively, and it's effort arm and effort are $d_2$ and $F_2$, respectively. Now my ...
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### Weight Suspended From A Springlike Belt [closed]

This situation is similar to the physics involved in a slack line, though I'm looking at it for some CNC applications. There is a 3meter belt, that is tightened to be under 200N of tension between two ...
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### How to replace these two forces with one force?

Here, $P>Q$. $O$ is the center of mass of the rigid and uniform bar/stick. As $P>Q$, the resultant is situated to the right of $\vec{P}$ and is parallel to $\vec{P}$. The magnitude of the ...