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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Statics problem from classical mechanics

I was solving David Morin's book on classical mechanics. In the solution for the second part of the "a" part of the question, why is the normal force defined as $Ndθ$ and not just $N$? Is ...
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Why isn't the moment always included in a free-body diagram?

Now I have seen many times both in my physics book and other books when drawing a free body diagram the moment is not included but the forces are. For example in 2d when a beam is fixed to a wall ...
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How does this tensegrity table work?

I have assembled below a desk toy which seems to defy laws of physics at first glance (objects can be placed on top of it up to a certain limit, since it is already under strain). The toy is in fact ...
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Why do period and damping ratio affect acceleration?

In the table above, the period of the structure $(T)$, the acceleration coefficient on the structure ($g$ in terms of gravitational acceleration) $Sa(T)$, The damping ratio is expressed as $ζ$ . As ...
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Does the law of the lever apply to all levers?

I recently posted a question involving the law of the lever, and I realized I was unclear on what it meant. I understand that, for a lever to be balanced, the effort force times the effort arm must be ...
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What determines the mechanical advantage of a lever?

This question is more specific than it seems. I am doing a mechanics-related project in class and we are learning about the functions of levers. Basically, I am confused as to what determines the ...
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1 vote
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Serway & Jewett's definition of rotational equilibrium

On p. 364 of Physics for Scientists and Engineers (9th ed.), Serway and Jewett define a rigid object to be in rotational equilibrium if it has an angular acceleration of zero. They then state that a ...
1 vote
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Can an Ideal Lever Balance in a Non-Horizontal Position?

I recently came across an interesting question while reading Feynman's Lectures on Physics. In chapter 4–2 "Gravitational potential energy," there's an illustration that made me wonder about ...
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(Opinionish) Feynman Lectures Exercise: Use principle of virtual work to show the following about $n$ forces in static equilibrium

I would normally not want someone to provide a complete and well-stated solution to an exercise. In this case, that is exactly what I am seeking. The following exercise appears in Chapter 2 of the ...
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Investigating the stability of a wooden block

Consider the above experimental design. At the end of the strip, at point $p$, a mass $m$ is attached, the stability of the wooden block above is determined by the angle $θ$ at which the block topples ...
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Mechanics/Statics: How to decide which statics problem can be modeled/solved in 2D or 3D? What are the steps to identify the dimension?

I am a first year mechanical engineering student. In statics we learn to solve/model different problems (free body diagram, sum of forces in $x/y$ etc...) in 2D and in 3D. But how to think about 2D? ...
1 vote
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Derive the ideal shape for a dome and a cylindrical arch

A catenary is the ideal shape for an arch whose job is to support its own weight. First, would this be true for a surface of revolution about a vertical axis through the lowest point, i.e. would a ...
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How to approach a static analysis when objects are on differing inclines?

I think this sort of problem is known and relatively simple when on a single angle of incline, but I'm trying to understand a problem with two points of contact of a uniform vehicle where each contact ...
1 vote
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What is the amount of force applied on my back while I'm brushing teeth leaning forward?

This is a question I've had for several years but never had the knowledge to calculate myself. Please keep in mind I don't have much background in physics (learned some on middle school I guess...), ...
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Proper treatment of springs in special relativity

I've looked on-line for a simple treatment of springs under tension/compression while moving at relativistic velocities parallel to the direction of tension/compression and could not find one. There ...
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On beam suspended by wires

My question involves sample problem 9-8 of the book "Physics" by Halliday, Resnick and Krane, 5th edition. So I could understand the answer given but there is something that is not ...
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How can the force acting at the fulcrum of a lever be calculated?

I know how to calculate the force applied to either or both ends of a lever system, but I would like to know how to calculate the force applied over the fulcrum of a lever.
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Adding mass to a bowl until it sinks [closed]

I've been struggling with this question. A hemispherical bowl of inner radius $r$, density $ϕ$ and thickness $t$ is floating in a fluid of density $ρ$. The bowl is being filled with sand at a constant ...
289 views

Calculating the sag in a cable that has two different weights (two wires joined together)?

I'm familiar with the equation for the sag of a cable: $$x = \frac{wx(L-x)}{2T}$$ Where w = the weight per length, T = the tension and L = the length of the span between supports. I'm wondering if ...
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Tensions in the chains [duplicate]

What is the physics behind this mechanism? What would be the free body diagram be like regarding all the magnitudes of the tension forces present in the chains?
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Tensions in the chains

What is the physics behind this mechanism? What would be the free body diagram be like regarding all the magnitudes of the tension forces present in the chains?
1 vote
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What is the physical explanation for $cm(h_{min})= h_{min}$ when minimising the centre of mass of a can of coke?

There's an undergraduate statics problem that is about finding the lowest centre of mass of a coke can as it is emptied out (say through a weightless straw). The problem itself is not difficult and ...
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Direction of the normal force [closed]

Suppose we have a bar with non-zero mass inside a hemispherical bucket fixed to the ground. Suppose, too, that there is friction between the bar and the inner spherical surface of the bucket. Part of ...
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Stability of a pile of dominoes [closed]

Consider the above figure; $n$ identical uniform dominoes, each of length $l$, are stacked upon each other in the presence of a uniform gravitational field. Find the maximum distance and the setup for ...
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Computing the strain in a cantilever beam under a known deflection

I intend to use a cantilever beam to calibrate a strain gauge, in a setup similar to the picture. My idea is to introduce a small known vertical displacement $\delta$ on one side of the cantilever ...
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I have a question regarding the calculation of the forces of a linkage in static equilibrium. Consider the mechanism in the figure. Points A and B can move in all 3 directions (hence they have 3 DoFs ...
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Stationary, static and strictly stationary/static?

Consider spacetimes which are asymptotically flat at null infinity. How to explicitly show that there exists a hyper-surface orthogonal killing vector field $k^{a}$ that is time-like everywhere in ...
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1 vote
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Why can multiple eggs support more weight per egg when there are more of them?

In this video by TAMU Physics & Astronomy titled "Eggs can support A LOT of weight!": https://www.youtube.com/shorts/a7JvE-fGrgg?feature=share The teacher first grabs an egg and places ...
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Accelerating fluid making an angle with horizontal [closed]

The proofs of the two equations (1) and (2) below are given at the end of this question in the last image. $$\frac{dP}{dy} = -ρg$$.......... (1) Where P is pressure and ρ is density of fluid. \frac{...
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Is the weight of something being dropped the same as the force of something being static?

If I have a block of let's say: 10 kg and I put it over my foot in a static manner, what we know from static mechanics is that my foot is opposing the weight of the 10 kg mass with the same force in ...
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How to calculate normal force acting on part attached with a screw? Can the force on screws be decreased by lowering the height of the normal force? [closed]

I have an L-shaped beam (equal height and width lengths) hanging from a screw on the wall, and I model the screw as a pin joint (hopefully okay approximation even though it does apply a constant force ...
82 views

Can a body be in both static and dynamic equilibrium simultaneously?

I was just studying statics when I realized that a body can be in both static or dynamic equilibrium at the same time but I am not so sure. My textbook says that an object at rest is in static ...
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Sign of distance/arm when finding moment/torque

I know that $M=Fd$, but when I have a negative moment, does the sign of the moment matter when I'm calculating for distance? If yes, then what would it mean when distance is negative?
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Origination of internal forces in a beam under axial loads

Take a prismatic beam and subject it to a tensile loading, assume we are applying a load of 10 N on both of its ends. As we know, the beam stretches by a certain amount on either sides. And since ...
125 views

Calculate weight distribution on 2D plane

I am trying to figure out how I can have a formula for the weight distribution on a square. But let me just describe what I am doing, We have the classical horizontal beam support problem And I we can ...
72 views

Intuitive understanding of the mechanism of uniform bending moment

So many explanations on uniform bending moment and I can't understand until now how it works. I can somehow visualise that in order to resist the external bending moments created by equal and opposite ...
1 vote
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How to calculate longitudinal force on two rods where each is fixed at one end to the ground and connected to each other at the other? [closed]

Imagine a 2D scenario. There are 2 rods. Both are fixed at one end to the ground (some distance away from each other). The connections to the ground are universal joints that are free to rotate. The ...
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Finding the tipping force for a cantilever table [closed]

How would I find the force it takes to the table to tip over if you were sit on top the cantilever end?
1 vote
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Weight distribution and support polygon

I was working on a problem of supporting an object with sticks and wondering about some use cases that would fail. My approach is to place the n-sticks (for example 4) under an object with mass m ...
1 vote
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Vectors forming a closed triangle

I've always been taught that vectors that form a closed polygon represent an object being at equilibirium, that is there is no resultant force on the object. However, this has never been intuitive to ...
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2 rods connected at a pivot and attached to a spring

I have a question concerning this problem First I calculate F1 by taking the origin at F2 and imposing equilibrium for the torque thus getting $F_1 = \frac{a}{a+b} F$ and similarly for F2, then I ...
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Is it possible to find the forces in this problem involving a block/beam/bar glued to the side of a wall?

This is a follow-up to a previous post of mine post. In that post, we concluded that a beam cannot be held in place by an application of normal forces in only one location if that location is off the ...
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Horizontal bar with one fixed end held by support beams touching/"pinching" it at one location to keep it from falling — Unsolvable problem?

Suppose we have a horizontal rigid bar held in place by two reinforcement beams (one above the bar and one below the bar), both of which are attached to a wall, such that they "clamp" the ...
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1 vote
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How do we pick the contact point for distributed contact forces?

Suppose I have two structures of three blocks of the same shape with mass 1.0. The structures are in the exact same poses. I have drawn two sets of forces that can satisfy static equilibrium. However,...
1 vote
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Water Droplet on solid plate (Young's Equation via Force Analysis)

I was reading about Solid-Liquid-Air Interfaces pg 484 in Competitive Physics Volume 1 by Wang and Ricardo and we were proving Young's equation regarding the contact angle of the water droplet on this ...
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Ladder against wall - reason for movement orthogonal source force?

Intro: I am under the impression movement is caused by a force, in particular without any boundaries a force causes an acceleration into the direction of the force. With boundaries, "the ...
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Plank overhanging off a building — where does the normal force go?

Suppose there is a (uniform rectangular) plank of mass $m$ and total length $L$ that is on top of a building with some piece overhanging or jutting out past the building. Assume it isn't past the ...
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How is a cupboard stable?

Take a cupboard or just a large wooden box. When pushed it a point above its center of mass, the cupboard topples because there is a net torque due to the friction and the force you apply. When pushed ...
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Parallel and concordant forces

I translate into English what is written in Italian in the adopted text. Two forces are parallel if they have parallel lines of action; two parallel forces are concordant if they have the same ...
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To obtain the resultant force, colored in purple, of two parallel and concordant forces $\vec{F_1}$ and $\vec{F_2}$, I apply a vector $\boldsymbol f$ (colored in brown) to the bar $AB$; similarly ...