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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Torque and equilibrium

I am a little stuck on the concept involved in part b) of the following problem: A $5 m$ long road gate has a mass of $m = 15 kg$. The mass is evenly distributed in the gate. The gate is supported at ...
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1answer
788 views

Solving an indeterminate triangle truss structure (statics)

From the setup of two trusses as shown in this illustration, how can I solve for the axial reaction forces in the trusses, and in the points A and B (Ax, Ay, Bx, By)? It is assumed that the joints ...
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2answers
1k views

How would you determine whether an object is at equilibrium? [closed]

How would you determine whether an object is at equilibrium or not? What is the definition of equilibrium?
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1answer
84 views

Summing moments, where have I gone wrong?

Because I don't have enough rep to post images, the question is question 3 part iii) from here: http://www.mei.org.uk/files/papers/m209ju_jk32.pdf The surface at the contact point B is rough. The ...
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3answers
335 views

Where does the extra equation come from to determine the forces from an object on a table?

I have a question about basic statics but somehow I cannot manage to find the answer on my own (btw, this is not a homework. It's been so many years since school for me...). The problem is very ...
4
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2answers
214 views

Why are some jenga pieces easier to remove than others?

Jenga is a game place with wooden blocks stacked on top of one another in an alternating pattern. Players take turns removing blocks from any layer and placing them on top. As the game progresses ...
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1answer
235 views

Tension in a closed loop around an object, carrying stuff

Sorry when this sounds like a first year physics homework question, but it's actually not. It arose during a discussion regarding safe practices for rock climbing anchors... So here we go: Imagine ...
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4answers
3k views

Upward force on a object at rest

Is there an upward force on a object at rest? If yes, where does it come from?
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1answer
562 views

Statics of Rigid Bodies — Can there be two possible solutions?

I've been working on a question and there seem to be two possible solutions. My own solution does not match the one given in the book. However, after resolving forces and taking moments with both ...
3
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3answers
162 views

Does a cross really have a smaller area moment of inertia than a square of the same area?

I need to calculate the area moment of inertia of a cross for a homework assignment. The cross is a symmetric plus sign: _ | | |== ==| | | - ...
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1answer
3k views

Problem solving moments in equilibrium

Two straight ladders, AC and BC, have equal weights $W$. They stand in equilibrium with their feet, A and B, on rough horizontal ground and their tops freely hinged at C. Angle CAB = 60$ ^o$, angle ...
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1answer
923 views

Application of Archimedes Principle

A candle is floating in a liquid placed in a container. The container is a cylinder of diameter $D$, and the candle is of width $d$. ($D>d$) The height of the liquid from the bottom of the ...
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1answer
150 views

Find the bending moment of a pole attached to a moving block

I'm having trouble with the following problem. What I've done so far: x-y is the usual coordinate system. $a=\frac{F}{m}=\frac{800}{60}$ and the y component of this is $a_y=a\sin{60^\circ}$. To ...
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1answer
1k views

Cylinder rolling down an inclined plane held by a string

A cylinder of mass M and radius R is in static equilibrium as shown in the diagram. The cylinder rests on an inclined plane making an angle with the horizontal and is held by a horizontal string ...
4
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1answer
1k views

Hooke's Law question

I have the following question to answer: a force of160 N stretches a spring 0.050m from its equilibrium position. A. what is the spring constant of the spring? The equation for Hooke's Law in my ...
6
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3answers
762 views

Force between two charged rods?

Suppose that we have two rods of length $l_1, l_2$ connected at one end but free to rotate. These rods have charge density $\lambda$ uniformly distributed, so the total charge of rod $i$ is $\lambda ...
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0answers
41 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. ...
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1answer
397 views

Internal forces in a truss and its geometry

I'm to work out the internal forces in a truss, but I can't get my head around the geometry of the truss itself. I'm starting to think there may have been information on the diagram which I missed. ...
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2answers
3k views

Calculating torque adjustment for offset of pivot point

I'm trying to figure out how much to adjust torque, on a torque wrench when using an extension that offsets the pivot point. See this calculator for a diagram of what I'm talking about: The trouble ...
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2answers
175 views

Additional mass of block on inclined plane

I would like some help in solving this problem. Height is 15 cm , base is 88 cm My attempt: $$(119.3 + m)(\sin(\theta)) = (88*9.8)$$ $$ 15^2 + 88^2 = 89.269^2 $$ $$ \sin^{-1} = 15/89.269 $$ $$ ...
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1answer
589 views

Calculation of a bending moment

I'd like to calculate the bending moment of a cantilever, fixed at its base, and submitted to a certain stress on a specific spot, but I can't find the proper definition of this bending moment (first ...
6
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2answers
1k views

Hydrostatic friction: why do water droplets stay at rest on an inclined glass surface?

Tjis is a non-expert question on a (seemingly simple) text-book topic. The question is about "hydrostatic friction", defined as follows. Consider a drop of water resting on a flat surface. If the ...
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0answers
299 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 $w$. $$w = A^{-1}\times q$$ ...
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0answers
141 views

How can I calculate all of the tensions in the cords? [closed]

I have been stuck on this problem for the last half, and to be honest I don't even no where to begin. I'm being asked to calculate all of tensions for the cords. I know I'm supposed to use $\cos$ to ...
4
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3answers
755 views

Hanging chain in a planet's gravitational field

The curve for a chain hanging between two poles in a uniform gravitational field is known as the catenary. Is there known an expression for the curve of a hanging chain on a planet of mass $M$ which ...
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3answers
240 views

Doubts with levers

I'm studying for a test of static rigid body and I'm having doubts on how to solve problems involving levers with weight. If I have, for example, a lever 10 kilograms and 3 meters long and one support ...
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3answers
1k views

Statics software for structural engineering [closed]

I'm attempting to expand my knowledge of engineering software. I've found comsol and ansys for acoustics and thermodynamics/fluid dynamics (not necessarily in that order), now I'd like to see if I can ...
3
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2answers
300 views

Bowling ball on a rubber sheet

After reading a layman's guide to general relativity, I began to wonder what shape a bowling ball on a large rubber sheet would produce. For simplicity, I would like to assume that Hooke's law applies ...
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1answer
539 views

Trying to understand the tension in a spring with two weights attached [duplicate]

Possible Duplicate: Why I think tension should be twice the force in a tug of war For (A) in this image, I would think the tension should be should be 2mg. However, my book says the ...
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1answer
520 views

Can I use Newton's second law to solve what seems to be a torque problem?

The Problem: An 8-m-long beam, weighing 14,700 N, is hinged to a wall and supported by a light rope that is attached 2.0 m from the free end of the beam. If the beam is supported at an angle ...
3
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1answer
164 views

Can structural trusses in centrifuges be helpful at all?

Imagine a rotating space station for the purpose of creating artificial gravity. Generally, such a space station is portrayed as a ring or a cylinder. Images of these space stations often have lines ...
4
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1answer
2k views

Solving a statically indeterminate truss

I'm trying to solve the statically indeterminate truss shown below and I'm having a little trouble. $H$, $P$ and $\beta$ are given. The material is aluminum (density is 2700 ${kg/m^3}$) and has a ...
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1answer
119 views

Force in tetrahedron edges

I am looking for a formula that enables me to calculate the force in a tetrahedron edge such that it relates $F_b$ with $F_z$ through the beam thickness and length. I have the following assumptions: ...
3
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0answers
132 views

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 ...
4
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1answer
2k views

If 1 screw can support 120 lbs, how much weight can 25 screws support?

While this is mainly about my personal home improvement project, I figure this would be a good opportunity for some of you to apply your physics skills to a real-world situation. My situation is ...
4
votes
1answer
668 views

Understanding moments as forces?

I was watching this lecture on analysis of stress for mechanics of materials. At time 7:20, the lecturer says that in equilibrium, the sum of forces and "moments" in each direction (x,y,z) must be ...
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1answer
454 views

Calculating torque in a structure

I posted this on math stack exchange but realize it is more a physics question. I have a structure which is set up as shown in the image. A weight hangs from point A with mass $m$. Joint B is free ...
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1answer
2k views

Relationship between balloon size and pressure

I see numerous websites talking about how a small balloon is at higher pressure than a big balloon. This is a fun counter-intuitive factoid... unless it isn't a fact at all. Young-Laplace gives $$T ...
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2answers
1k views

Calculate the weight a simple plank can support [closed]

I'd like to build a simple desk; just a single plank of wood (or a few side-by-side) with solid supports on each end of the desk. What I'm trying to figure out is how thick a plank I want to use for ...
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2answers
3k views

Calculation of the maximum load to the bar

Looking for a way of calculating the maximum weight (W) to the rod with the given length (L) where the rod did not break and that only bend for (b) mm. Need only approximative solution (read: ...
3
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1answer
1k views

Why does the beam in a weighing balance get tilted proportional to the weights added to each pan?

I'm talking about a beam balance(a simple weighing balance with a beam and two pans hung on either side) As answered in a previous question, the beam comes back to the original position when one ...
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2answers
386 views

Hanging a Hammock

I have a hammock that I want to hang using a tree on one end and a wooden post set in a bucket of cement on the other end. How would I determine how heavy the cement needs to be so that it would ...
0
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1answer
432 views

Hinged bridge statics problem

For part (a), is the normal force by the hinge on the bridge at an angle or is it horizontal? For part (b), I know how to resolve forces horizontally and vertically, and to take torques about the ...
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1answer
1k views

Calculating mass of object by lifting edge

Assuming a solid rectangular plate, hinged along one edge. How does one calculate the mass of the plate if the force necessary to lift the opposite edge is known?
2
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1answer
366 views

Poisson effect formula for large deformations

English Wikipedia in the Poisson's ratio article gives an equation for large deformation: $$ \frac{\Delta d}{d}=-1+\frac{1}{\left(1+\dfrac{\Delta L}{L}\right)^\nu} $$ I couldn't find any reference ...
2
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2answers
1k views

How do you weigh a box on a scale whose limit is too low?

As you will see I know nothing about physics and after being asked to solve a physics problem in a recent interview wanted to ask it of professionals and see what the response would be: I have a set ...
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1answer
273 views

Bridge Trusses? [closed]

Which kind of truss would produce the best result (aka. best distribution of force): i) An equilateral, isosceles or a scalene triangle ii) 3 small triangles or 2 big triangles (the overall masses of ...
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1answer
509 views

Problem in a truss [closed]

For the truss above known are the following: l= 1 + 0.02*n [m], h = 2 + 0.01*n [m], F_1 = 200 + 2*n [N], F_2= 500 + 6*n [N], F3 = 400 + 5*n [N], Young's modulus E = 2*10^11 [N/m2], allowable stress ...
3
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3answers
3k views

Deadlifting the rear end of a car with a lever. What it equates to in actual weight?

Consider this youtube video of a guy lifting a car. (skip to 2:15). I checked, and these cars (PT Cruiser) weigh $1417\:\rm{kg}$. What would the equation be to estimate how much weight he is actually ...
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2answers
3k views

How do I find the tension in additional strings in this problem?

A mass of 5.00 kg hangs attached to three strings as shown in the figure (see image below). Find the tension in each string. Hint: Consider the equilibrium of the point where the strings join. ...