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
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The Physics Behind the American Death Triangle [closed]

I've heard a lot about the American Death Triangle and how it is awful for belaying. The Death Triangle is set up as such: you have two anchor points with a single rope or line running through both ...
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1answer
1k views

Calculating force with two fulcrums and many forces [closed]

I may not be wording the question the right way. I have a lever. About 2/3 the way back there is a pivot point. We'll call this B On the very front (end of the lever) there is a block that the lever ...
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3answers
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Do supports exert torque?

I think I'm missing something about torques. Do supports exert torques? Consider these two situations I'm confused about. A rod is attached in to a wall so that it cannot rotate. Since weight exerts ...
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1answer
429 views

What are the clicking sounds when static electricity occurs?

Sometimes, when there's static electricity, soft clicking sounds can be heard. This may happen when two fabrics are rubbed or when you get a static shock. What exactly causes this sounds?
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0answers
87 views

What way did this person solve the problem? [closed]

Im curious, I have no idea how they solved the problem to get from the unitary vector to the Moment/Tension. How did they managed to get it so reduced? What steps did they perform in the blue part?
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1answer
534 views

Maximum Load of a Crane before Car will Tip

Imagine a car with a crane. In scenario 1, the tension on the crane cable by the load points straight down, ie, perpendicular to the ground. In scenario 2, the tension on the crane cable by the ...
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1answer
174 views

Interpreting force components in statics problems involving inclined planes or similar

I'm having troubles to understand how to interpret the components of forces on inclined plane in quite complicated situations. I will make an example of one of the cases where I get confused. ...
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2answers
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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 ...
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1answer
101 views

Homework Question: Moments [closed]

Can someone please explain this question? My work: If we take B to be the pivot then as B gets closer to mg the torque due to mg gets smaller, but I don't really see how this affects the force F (I ...
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1answer
14k views

Calculating the tipping point of a lamp post

So I'm designing an outdoor lamp post and trying to calculate whether it will withstand the heavy winds at the worst case scenario. Here are the parameters and what I've done so far: The lamp post is ...
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1answer
147 views

Laws and Intuition for physical problems

So I've been reading the book 'Feynman: Tips on Physics' recently and in chapter 2 (the book is available for free online) he works out the answer for this problem using his intuition rather than ...
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1answer
18k views

Determine resultant couple moment by summing moments

The question states: Determine the resultant couple moment by (a) summing moments about point $O$ and (b) summing the moments about point $A$. I used scalar analysis for solving this ...
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1answer
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Converting loads on horizontal surfaces to inclined surfaces

A textbook on design of wood structures makes the following argument: We have a flat roof snow load $$S_1 = 61.6 \frac{lb}{ft^2}$$. The idea is to convert it to an equivalent sloped roof snow load $...
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3answers
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Tension in rods (basics)

I have a problem understanding these basics. What is the tension in the ground rod due to the forces exerted by the slanted rods? Please feel free to correct me at any point. Rods are idealized and ...
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1answer
2k views

Static Equilibrium [closed]

A 3 Newton force and a 4 Newton force are acting concurrently on a point. Which force could not produce equilibrium with these two forces? 1N 7N 9N 4N I'm confused. The book I'm looking at says that ...
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1answer
286 views

$16~\rm N/mm^2$ flexural strength

This question more relates to construction and architecture but I am sure it will not be the problem to ask and get a good answer here. If we have declared flexural strength of concrete of 16 N/mm2, ...
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4answers
567 views

Newton's Third Law As Discussed in Den Hartog's Mechanics

A question, but some preliminaries in order to avoid answers involving concepts not yet introduced in the text I'm reading--Den Hartog's Mechanics. Near the very beginning of his book, Den Hartog ...
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1answer
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Not sure how to solve a problem from online course [closed]

I'm not sure how to approach this problem. I don't know the magnitude of F1 or F2 and I'm not sure how to get it from F. Any help would be appreciated.
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Why don't barbells tip over when a 45 is placed on one side?

A standard barbell is 45 pounds, as is the heaviest weight available in most gyms. When a weight is placed on the side of a barbell, some of the barbell is to the "outside" of the weight, like so, so ...
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0answers
417 views

Tension on wire holding open door, using moments about a hinge? [closed]

Using moments about the hinge, what is the tension in the wire holding the door open? The wire is horizontal. The door is 5m. See diagram: The door is at tan inv (3/4) : 36.9 deg to the horizontal....
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1answer
63 views

When an object hangs from a Rigid rod is the force of the weight located in the center of the sign?

From the rope that supports the sign (assuming the mass is distributed evenly). If the length of the sign is, $L$ can I model it so that the weight is concentrated at $\frac{L}{2}$ Therefore, the ...
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0answers
131 views

Applied forces on a bridge [closed]

What are the forces that acted on the 6 types of bridges? Beam, Truss, Cantilever, Arch, Suspension, and Cable-Stay? What formulas do you use to get the forces? I'm curious since there is nothing ...
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2answers
439 views

how does one divide stress in such a bridge? [closed]

I want to build a spaghetti bridge like this: I have two spaghetti types: T-type (designed to tolerate tension) and C-type (designed to tolerate compression). A mass $m$ is hanging from the point ...
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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. ...
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1answer
323 views

Difference of water pressure

We know that $P = \rho gh$, so is it true that water pressure at 2nd floor will be higher than water pressure at 9th floor of a 12 story building?
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1answer
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Confusion about two-force members

This is my first question here so I hope I get warmly welcomed by answers that would resolve this perplexion :-) This is a statics problem from Hibbeler's Mechanics for Engineers: Statics (13th ...
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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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2answers
869 views

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 $10 \,\text{N}$...
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2answers
490 views

Equilibrium equations

You have one horizontal beam. Its left point is attached to a free pivot at the vertical wall. Its right point is suspended by a rope from the ceiling. Nothing is moved. So $\sum F=0$ and $\sum M=0$. ...
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2answers
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I'm building a bubble pane. What can I do to reduce static pressure? [closed]

I'm building a bubble pane, just for decoration in my home, using some patio door glass panes and an aquarium air pump. Soon into my testing, I learned what static pressure is. When I fill it up, even ...
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1answer
61 views

Distortion of non-circular cross sections upon torsion

True or false? Non-circular cross sections can be non-planar when torsion is applied. This was on a quiz today and I wasn't sure of the answer. I guessed true by intuition, but does anyone have a ...
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1answer
462 views

push up weight distribution [closed]

I'm about 84 Kg, in push up position (hands on the scales) the scales show about 54 Kg. Can anyone explain briefly the physics of the weight distribution? (I did high school physics decades ago - can'...
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866 views
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How is normal force distributed along the surface of contact?

Help me settle this argument. A mass $m$ is placed on a thin diving board. The base of the diving board has mass $M>>m$. Does the board tip over? I drew the following FBD and concluded there ...
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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 ...
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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). ...
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1answer
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A question on Rolly polly dolls

I was reading on rolly-polly dolls when the following questions crept into my mind How exactly does center of gravity play a role which helps rolly-polly doll to stand up on its own? Can a rolly-...
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2answers
517 views

Planks, supports, and a scale [closed]

I've got two equal dimension planks with the same homogenous mass. They're placed next to each other like this (bird's eye view): [ ][ ] They're sitting ...
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1answer
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How to calculate Young's modulus from a set of data?

The set of data are force vs deflection. Is Young's modulus constant for a material? If the beam is fixed by one fixed support and one vertical support $E = \frac {F}{δ}\frac{3.5L^3}{384I}$
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5answers
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How is an object kept on a table is at rest?

When there are two bodies A and B lying in contact we can apply Newton's third law which says that the action and the reaction act on different bodies and not on the same body. That is why two forces ...
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1answer
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Why is it effectively impossible to balance this rectangle block on a triangle block? (See photo)

I've always wondered why it's basically impossible to balance a rectangle block on top of a triangle one like this. This is my nine-year-old giving it a try. I have never in my life gotten it to ...
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1answer
910 views

How exactly do walking canes and crutches help?

I am reading introductory physics, and there is a chapter on equilibrium. In the chapter, the author mentions how devices can exploit distribution of forces to help those that are physically ill, via ...
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1answer
351 views

Tension along a curved surface [closed]

I'm curious what the tension in a rope will be when its exposed to a uniform load. Assuming a similar setup to this question what will the tension along the rope/tube be?
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1answer
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Simple Beam Worst Case Scenario

Part 1 If I have a simple beam with two supports and a static load, does placing the load in the center push the beam closest to breaking (catastrophic failure)? Will this be more likely to break ...
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1answer
977 views

How to design a stable table?

Imagine a round table, standing on one central leg. The central leg has a base for balance. That base is what I am referring to. What physics do I need to understand to design a stable table? For ...
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4answers
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Two people are holding either end of a couch, is one person exerting more force than the other?

I was carrying a couch with my flatmate yesterday, and I started thinking about this. Often when carrying objects like this, one person will be taller and has thus lifted his end of the couch higher ...
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2answers
3k views

Connection between moment/torque and centre of gravity?

So I understand how moments work with regards to basic examples like pushing a door, in that the further you are away from the hinges of the door, the greater the moment, which is like a turning force....
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1answer
65 views

Half of a uniform disc suspended by two strings [closed]

Suppose we have a half of a thin, homogenous disc hanging from the ceiling as shown: Given the weight of the disc $Q$, calculate tensions in strings $S_1$,$S_2$. Now this seemed like quite a simple ...
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2answers
259 views

Formula for balance with three arms?

I'm searching for a way to express the angle of the arm of a balance instrument expressed in the weight that is present in one arm. For a two legged balance one could use the moment formula: moment = ...
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1answer
167 views

How to find the spring coefficient of a simply supported beam?

So I've been searching wikipedia and google but nothing can show how to find the spring coefficient of a simply supported beam with a uniformly distributed load. The spring coefficient, $k$, is ...