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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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1answer
16 views

Can the equivalent point weight extend beyond the body on which it acts?

If the x location of the centroid equals (moment about O)/(equivalent point weight) and there are forces acting above and below the given body, couldn't the value of the x coordinate potentially ...
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2answers
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Where to put weight so that 2 jointed rods are most likely to slip? [closed]

I'm doing the attached mechanics question for school and would like to know exactly why you the man standing in the middle of the system increases the likelihood of the system slipping. The solution ...
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What is the resultant force acting on a body when two equal and opposite forces act on it?

I feel I am missing a key intuitive insight into understanding a problem like as follows: (Sorry for rough drawing) The system above consists of a hammer, floor, and a ball in between those two. When ...
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Question in measurement uncertainty calculation in projectile motion

For a projectile motion, $\displaystyle t=\sqrt{\frac{2y_0}{g}}$. If you look at page 6 of the article(http://www.hep.vanderbilt.edu/~maguirc/Physics231/p231_lect3.pdf), the fractional uncertainty/...
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Can we construct a (specially designed) truss that is horizontal when supported from one end?

It is not possible to support a horizontal beam from one end, and the same is true for an I-Beam. I believe this can also be proven for a pipe, but that proof is just outside of my reach. But all of ...
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1answer
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Statics and equilibrium of a rigid body [closed]

A vertical cylindrical container contains within it three identical spheres of equal weight P which are tangent to each other and also to the inner wall of the container. A fourth sphere, identical to ...
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5answers
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Which explodes first? Vacuumed tank or pressurized tank?

We have been arguing with a friend and couldn't agree. Here is the question: We have two systems. In both of the systems, we have an identical sphere tank. In the first system, we are vacuuming the ...
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1answer
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Why the weight force is not included in this free-body diagram

Take a look at this question. The solution by the author is My question is why the weight force is ignored in the free-body diagram? Is it because the roller(A) and the pint(B) which cancel the ...
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3answers
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How the ladder will slip if the wall and ground were to be smooth?

If I have a situation like this Where my blue thing is wall and the yellow thing is the ground. If both were to be smooth then they will exert a contact force only normal to them which I have ...
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1answer
19 views

Center of mass of a rotating object

I read that if the left block moves up by $dx$ then the center of mass of the rotating object moves down by a vertical length of $\frac{1}{2}dx\sin(\phi)$ but I thought it would move down by $dx\sin(\...
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Work on an object in equilibrium

I heard somewhere that when an object is in equilibrium on the flat bottom of a hill that it will require work proportional to $dx^2$ when moved the small distance of $dx$. I thought that it would be ...
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1answer
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Determining the $z$-component of a force to maintain equilibrium?

I came across this problem in vector mechanics wherein I’m asked to determine the value of $d$ such that the tension in cables $AC$ and $AD$ is half the tension in $AB$. What I initially did was ...
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How to determine the direction of components of force while solving the problems related to hinge force? [closed]

There are two different directions of horizontal force in two different situations. Why?
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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 ...
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1answer
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If two hooks support weights on a string across a span, how much weight can it support?

Assume there are two hooks, each rated as able to hold 5 pounds. They are both mounted to a wall, one at the north end of the wall and the other at the south end of the wall. The wall is 10 m long. If ...
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2answers
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Rules for constructing new axes for resolving a force [closed]

Take a look at the following picture Obviously, constructing $u-v$ axes allow us to resolve the force into two components. My question is what are the rules for constructing such axes? It seems to ...
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1answer
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In a truss, where is the reaction force acting on?

A truss, its free body diagrams and also of the pin at C is shown in the figure. Ay and P, in figure II may be equated because they are acting in opposite direction on the same body(the whole truss), ...
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2answers
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Static friction in a slope and two boxes problem

The context: Calculate the string tension in the situation where two boxes are stacked on a slope and moving with uniform velocity, given that the kinetic friction coefficient between the heavier (...
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0answers
56 views

How far should I fill up a water bottle to make it the most resilient to accidental bumping? [closed]

I came across a situation similar to the one in the picture shown below, where you have a water bottle that is being knocked over by accident. Naturally, I wondered how much I would have to fill a ...
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1answer
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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 ...
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0answers
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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 ...
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5answers
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Why does a force divide equally on multiple supports/legs?

Imagine a bridge spanning across two pillars/supports with a weight of $80N$. {Any external forces affecting the system are assumed to be negligible.} We know that the force exerted on these 2 ...
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2answers
75 views

Why is the weight multiplied by 2 and not one for this moment question?

Hi, I have my physics gcse tomorrow and in my CGP guide, to find the anti-clockwise moment they multiplied the weight by 2 and not one even tho it says 1m on the right of the pivot, is this due to the ...
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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 ...
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0answers
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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 ...
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1answer
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How is weight dispersed among multiple points?

I was recently viewing remembrance photos from the 1995 bombing of the Alfred P. Murrah Federal Building on MSN news where slide nine shows a photo of firemen teaming up to carry a $40'$ steel bar ...
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1answer
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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 ...
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1answer
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5.61b University physics with modern physics [closed]

$$ \sum F_{y} = 0 $$ $$ \sum F_{y} = T_{1y} + T_{2y} - mg $$ $$ mg = (4400N)\sin{60} + (4400N)\sin{40} $$ $$ mg = 6640N $$ Why is this wrong? solution $T_{1x}$ has to be equal to $T_{2x}$ $$T_{1x} ...
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2answers
266 views

Tension in a string, at an angle [closed]

This was a question on a mechanics exam. Part i wants me to assume that the tension in both parts of the string is the same. Even though I got the correct answer( 18.9N) by assuming so, I don't ...
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1answer
78 views

A mass is hung from the centre of an unstretched, horizontal wire. How do I work out the depression of the centre of the wire? [closed]

A wire of unstretched length $l$ is extended by a distance $10^{-3}l$ when a certain mass is hung from its bottom end. If this same wire is connected between two points that are a distance $l$ apart ...
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2answers
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Confused about forces acting in this simple statics problem

I'm trying to solve this statics problem to find the internal tension that results, in each member: It shows 3 idealised weightless rigid members hinged in a vertical plane, in an isoceles triangle. ...
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3answers
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What is the physical origin of buoyancy?

Imagine a horizontal cross-section $\Delta S$ of a cylinder containing a liquid of density $\rho$. The downward pressure on $\Delta S$ at the depth $d$ from the surface of the liquid is $P_{down}=\rho ...
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2answers
117 views

How to interpret explicit moments in beams?

Consider the beam in the picture above. There are several forces that cause moments around all points in the beams. But there is also one "explicit" moment: 20kNm. How do I interpret these kinds of ...
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3answers
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Deriving an integral in a mechanics problem (massless string holding up a disk)

I am told that a massless string is holding up a disk of mass $M$ and radius $R$. I want to find out the value of the tension $T$ in the string. The textbook does this trivially by stating that $2T=...
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1answer
567 views

How do I know whether members are in tension or compression when using Method of Sections?

So we started doing structural analysis in my engineering class lately, and are doing trusses. However, I'm not quite sure how method of sections works conceptually. I'm getting the right numbers, but ...
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1answer
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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 ...
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1answer
35 views

In fig we have a block (shape $A$) that a rod is connected to it (shape $B$)

In fig we have a block (shape $A$) that a rod is connected to it (shape $B$) let that this system is stationary . Now I know that free body diagram is : Thus $$A : \vec{i} :T_{BA}=f_{s}$$ $$A : \...
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1answer
47 views

Formula for would something fall over or not?

Let's say I have a 10cm x 10cm x 50 cm wooden stick that weights 5kg total. The 10cm x 10cm base is touching the floor and it protrudes from the floor 50cm which is the height of the stick. Based on ...
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1answer
158 views

Three Dimensional Torque on a Sphere

Assume that we have a sphere in 3D space. Let point $A$ rest on the surface of the sphere. I can apply a force $F$ of any magnitude and any direction, so long as it points tangential to the surface ...
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1answer
336 views

Magnitude of F about line CD (Mechanics, 3D vector system)

I am having trouble with this question: I will write out the question below to make it easier for other people googling the question to find it: 2/139 If the magnitude of the moment of F about line ...
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0answers
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Good book on Statics and Dynamics [duplicate]

Could you please suggest a good book on statics and dynamics. The portions I have to cover include Statics : Equilibrium in 2&3 dimensions, Virtual work,Common catenary etc Dynamics : ...
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1answer
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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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0answers
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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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2answers
153 views

Magnetic levitation against Earnshaw's Theorem?

Given six strong magnets, what if we fix three of them to a table in a simple, horizontal, equilateral triangle-like formation (with their north poles sticking up), and the other three to the points ...
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2answers
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Why are ropeway pillars tilted?

While skiing I have noticed that ropeways pillars are usually tilted to be perpendicular to the slope (fig.1). If the gravity is pulling straight down, why aren't they vertical as they are supposed to ...
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1answer
54 views

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 ...
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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 ...
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3answers
101 views

How does beam pinned at one end resist moment?

This beam is constrained by a pin at one end, so it is free to rotate around that point. If a moment M is applied, the beam cannot move since any rotation would involve motion of the COM, which is not ...
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1answer
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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 ...