# 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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### How can one conclude upward force is related to tension in this question?

In preparation for the SAT Physics Subject Test, I have been doing extra practice problems. This one states: A garment bag hangs from a clothesline. The tension in the clothesline is $10 \,\text{N}$...
0answers
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### Obtaining point of application of Ground Reaction Force with use of a hyperstatic load-cell array platform

I'm looking for the theory of an experiment that is giving me a hard time to perform. I have an instrument composed of a rigid horizontal square plate rigidly supported under each corner by a load-...
1answer
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### Pressure of rubber band on cylinder taking friction into account

Suppose I have stretched a rubber band around a cylinder of radius $R$ such that the rubber band is under tension $T$. My understanding is that in the ideal situation, with no friction, the band ...
2answers
202 views

### Conceptual Question about Suspension Bridge Forces

Two walkways are suspended from vertical rods. In the first scenario, one long rod supports both walkways and is attached to the ceiling. In the second scenario, two shorter rods are attached to each ...
2answers
675 views

### Static equilibrium question: Horizontal rod attached to a wall

I'm doing a problem on static equilibrium and I'm unclear whether a force exists or not. This is my force diagram: The setup is: a homogenous rod with a certain mass is attached to a vertical wall on ...
2answers
2k views

### Angles in a static equilibrium

I have three masses $\left(F_\alpha, \, F_\beta , \, \text{and} \,F_g \right)$ with 2 pulleys, and a wind variable which is in static equilibrium. I have already calculated the appropriate forces for ...
2answers
401 views

### Determine the point at which moment vector is zero on a 3D body

I have information about total force and moment on a body for three points, whose coordinates I know. From this information I would like to determine the point at which moment would be zero. ...
0answers
66 views

### Dropping vertices of an overdetermined statics system graph

In statics, the problem of determining the tensions of K cables that connect a structure made of N points and keep all points in static equilibrium implies $ND$ systems of equations, where $D$ is the ...
0answers
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### Mechanics of Materials (pressure and temperature)

A solid right cylinder of rock core is surrounded by four rods made of mild steel (all-thread rods). The rods are placed equidistantly around the core in a square formation. The tops and bottoms of ...
0answers
25 views

### How to solve 3-variable planar vector equilibrium problems?

While it's quite straightforward to solve problems with multiple planar vectors in equilibrium for 2 variables, I'm having issues with those where I'm asked to minimize or maximize a variable along ...
1answer
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### Teeter Totter Team Building Game

I recall doing a team building exercise where a team of about 4 people needed to balance a teeter totter, so that neither of the ends was touching the ground. They could achieve this by having the ...
0answers
36 views

### Conservation of percent difference?

I was doing a lab to experimentally determine coefficients of static friction between two surface. This was the basic set up: The mass of the block is a known quantity. I was checking the maximum ...
1answer
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### Forces on Bifolding Door with horizontal hinge

I'm a programmer who's been put in charge of some motor control problems and I need your help, so please forgive me if the question is silly. The problem in question (see inserted picture) is ...
0answers
159 views

### Counting experiment and standard error

I have a counting experiment: Let's say I have N identical bees. I take one of them, expose it to $\gamma$-radiation and look if it has died or survives. If it survives, I count it as 1 count. If it ...
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### How to consider another Cartesian axis?

Well, I solved the problem. The point is that I used a x and y axis with x parallel to the inclination of the box, but I wanted to think differently, if one considers the y axis itself containing the ...
2answers
565 views

### Influence of couple-moment's position on bending moment diagram

The moment of two equally opposing force would create a couple-moment. Since the couple-moment value is invariant to the point considered to calculate the couple-moment, I can replace the two equally ...
1answer
36 views

### Transferable force

If I for example have two rectangular pieces of steel that are both W=40mm, L=1000mm, H= 40mm and are both completely ridged. One piece of steel is resting on top of the other piece of steel, if I ...
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### Why the sum of deformations in given figure is zero?

When a vertical block is kept between two fixed support and when the bottom support is removed, it has the possibility of facing a deformation downwards which was impeded by the upward reaction force ...
1answer
12 views

### How a stick can provide both normal force nad tension?

This is what I think. Please tell me, am I right?? If an external pulling force is applied on one end then there will be tension in opposite direction. And if an external pushing force is applied on ...
0answers
13 views

### Moment about axis with force applied at non-parallel line

I understand the process to solve the moment of a force at a given point applied about an axis. However, what if the force was instead applied to a second, non-parallel? Perhaps a physical example is ...
1answer
29 views

### Static equilibrium (possibility)

In static equilibrium for a ladder leaning against the wall it is supposed to rotate about a point. Why we are not assuming it to slide down as in our practical life?
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### Simple beam deflection of cantilever beam

Recently I had need to prove the beam deflection equation for a simple cantilever beam with a point load at the end. The equation would be in reference to the Euler-Bernoulli theory taught in most ...
1answer
28 views

### Friction Behavior at corners

The question: Find the range of value of $L/D$ such that the system remains in static equilibrium. And explain why such a range exists and not just a single value. This is the question where I ...
1answer
49 views

### How can I measure some forces in this experiment…? (statics)

Math and statics weakling here trying to do some... math and statics. I have an experiment where I'm trying to measure forces along 2 axes. I currently have a setup that I think might give me the data ...
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57 views

### Derivation of friction in interleaved phonebooks

Trying to understand the simple model in https://arxiv.org/abs/1508.03290, describing the friction between the pages of two interleaved phonebooks. Specifically I don't see how to get Eq. 1. Here's ...
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### Rotor finds equilibrium in TWO positions, why and how?

I have a Mendocino motor, a toy with magnets, solar panels, and coils. Such a thing requires careful balancing (eg. with tiny bits of tape) to achieve sufficient balance that it will start rotating ...
1answer
32 views

### Stability of a falling object

Suppose there is a falling object that has flaps around it providing resistance to the non-contact force of gravity. How would the vehicle theoretically not flip over? From my understanding, the ...
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### What stresses should be considered to determine the effective stress and FOS?

This question I tried to solve by considering the torsional shear and transverse shear and axial loading. But the answer is not clear. But the answers that I got by different trial and error method ...
1answer
878 views

### How to know what method to use when finding resultant forces?

I am quite confused as to what method should be used when finding resultant forces. Here are two examples of a question that asks to find the resultant force. One requires the parallelogram law to ...
1answer
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### Why conceptually cut a beam or else? (method of sections)

This question is related to structural design, and statics: When studying a beam, for example using the sections method, why do we make a conceptual cut?
1answer
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### Method of joints: The direction of forces

I have the following question: I need to find the load in truss element DF. I calculated the reaction forces at E and D. Fex = 360 KN Fy = 405 KN Then, I used the method of sections at point F ...
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### Balanced forces in scales

We have scales-like mechanism with a spring. Rigidity of the spring $C=10\ \mathrm{kg/cm}$, initial length $L_0=60\ \mathrm{mm}$ and diameter $d=\ \mathrm{10mm}$. Without any weight the scales are in ...
2answers
431 views

### Pressure of the same mass of fluids of different densities?

Suppose I have 2 fluids of different densities, and I pour the same mass of each fluid into 2 identical cups. I feel like I'm confusing myself here — on one hand hand, both cups contain the same mass ...
1answer
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### Force couple simplification

How is it possible to add all the force components to find resultant when forces are acting at different points on the body?
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### Axial loaded bars problem

I completely disagree with the following calculations: Based on my understanding, there is no force either internal or external applied to the Green bar, so it should be 0N. The reaction (internal) ...
0answers
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### When a force applies to a rigid body at point, then does every part of the body experience the same kind of force?

Suppose that a rigid body is static under the action of several forces that are applied at different part of the body. Then is it true that if one divides the body into small pieces, then each piece ...
0answers
55 views

### How do I minimize the the stress created by fore-aft forces?

My friends and I are designing a bench press spotter. Essentially, when the user needs help lifting the barbell due to muscle fatigue, an arm on each side of the user raises to provide assistance. ...
0answers
790 views

### How to solve fixed-fixed beam with finite difference method?

What equations to use on this system to form a matrix $A$ with dimensions $[n,n]$ and load vector $q$ with dimension $[n]$ ? I am trying to get vertical displacement $w$. $$w = A^{-1}\times q$$ ...
2answers
978 views

### Varignon's theorem (Principle of moments) failure?

Varignon's theorem states that "If many coplanar forces are acting on a body, then the algebraic sum of torques of all the forces about a point in the plane of the forces is equal to the torque of ...
3answers
483 views

### Static friction free body diagram on a flat plane

Do you include static friction on a free body diagram for a static box on a flat surface? Or do you just include Force of gravity and Normal force? We know when the box is moving there is Frictional ...
1answer
108 views

### Statics: What it means if a rope snaps

There is a drawbridge that is held up by a hinge attached to a vertical wall on one side, and by a vertical rope on the other side. Say a horse starts walking from the wall towards the rope and at a ...
1answer
281 views

### Truss analysis how to calculate for a single beam?

Suppose I want to calculate the tension/compression force only in 4. Is there an easier way to calculate it or do I have to calculate everything with the joint method? I don't immediately see zero-...
1answer
413 views

### Best self-study books for static mechanics problems

Which book is the best for me to self-study/improve at static mechanics problems? I am looking for a book with a lot of ( only ) problems, not a theoretical book. Not only basic problems, the ideal ...
1answer
211 views

### Membrane shape under pressure

If I have a circular membrane that is fixed by the edges and then I apply a uniform pressure to the membrane (let's say the membrane is the top of a circular chamber that has a rigid wall and flat ...
1answer
369 views

### Lever Mechanical Advantage

In the attached image the force output of the plank is calculated to be the work done (FDf) divided by the height the block rises (Dw). So the force the plank applies on the block is (FDf)/(Dw). But ...
1answer
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### Why can't we have more than 3 moment equations in equilibrium equations

Excuse me for a kind of stupid question but, In statics of a 3D rigid body, the equations to determine equilibrium are at most 6 (Fx Fy Fz Mx My Mz = 0) (not counting those from hinges and rollers). ...
1answer
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### What does $\bar{x}_{\textrm{el}}$ represent?

In the context of centroids and moments, what do $\bar{x}_{\textrm{el}}$ and $\bar{y}_{\textrm{el}}$ represent? For example: $$\bar{x}L = \int \bar{x}_{\textrm{el}}dL$$ Some references that use ...
1answer
3k views

### How do I know which force to use in moments calculation?

I'm working on some Statics problem, with the method of joints, etc and for all of them, we use sum of moments = 0. However, I'm very confused about which forces I should use to find the sum of ...