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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2answers
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Moment of a force about a given axis (Torque) - Scalar or vectorial?

I am studying Statics and saw that: The moment of a force about a given axis (or Torque) is defined by the equation: $M_X = (\vec r \times \vec F) \cdot \vec x \ \ \ $ (or $\ \tau_x = (\vec r \times ...
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Is there any situation where one can measure force WITHOUT motion?

I am drafting a patent application where one part of the invention measures a force. I'd like to distinguish this from the prior art, which measures a displacement. But for all the force measurement ...
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2answers
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How to calculate the supporting force exerted by a stationary object (cupboard) and support (brackets) for it?

I have a wall mounted Stuva Ikea cupboard, which measures 60x64x30cm. The base is 64x30cm. It is already supported by 2 holes at the back base, (64x60cm). But I need to add in L shape brackets ...
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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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2answers
232 views

Confusion about force analysis in 3D space

A book I'm using states that it is possible for a system of forces to produce a net translational force with no turning moment if the line of action of the net force does not pass through the origin ...
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2answers
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Hydrostatic friction: why do water droplets stay at rest on an inclined glass surface?

This 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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2answers
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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
54 views

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?
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2answers
177 views

What is the direction of friction in this example? Why?

I have difficulty knowing the direction of friction on static structures. The structure of the image is on equilibrium, and the exercise askes the maximum force P that the structure can take. Would ...
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3answers
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Taking moment about a point

Let's say I have the following diagram: Since it's a fixed beam, I know that there will be three components acting on point A: 1) Force acting in x direction 2) Force acting in y direction 3) ...
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1answer
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Calculating forces in stucture [closed]

I know how to find the reaction at a A and E and they worked just fine with me as external forces. But I am not understanding how to find the forces at joints B and D, what is the approach ?
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1answer
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The Perfect Bridge [closed]

Is it possible to calculate the amount of weight a perfectly designed bridge(not necessarily known) can hold given certain parameters and under ideal and perfect conditions: amount and type of wood ...
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Confused about direction of friction

Question : The system of two blocks and fixed pulley are joined by a cable as shown. Determine the mass $\textbf{M_2}$ required for static equilibrium. All wheels and pulleys have negligible friction: ...
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2answers
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How does force transmit through a solid block?

If you take a solid block, say, a cube of side length $l$ with density $\rho$, you place it upon a solid floor, and you apply an external pressure of $p(x,y)$ on the upper face ($x$ and $y$ define a ...
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1answer
350 views

The direction of forces in statics problem

I was always confused on how we define the directions of the forces in equilibrium problems. Let's say I have a simple structure: In this case, I assumed that Ray and Rcy are pointing up to counter ...
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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 ...
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2answers
387 views

Find force $F$ for equilibrium? [closed]

The masses of all the objects are mentioned inside them. Masses of both inclined planes are same and angle of inclination is same too.The inclines are smooth and the bar is Rigid. We have to find ...
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1answer
133 views

What is the force a man exerts on a ramp in equilibrium?

Today in our Physics class, we learned about static equilibrium of solid rigid. The teacher presented us with an example in which a man was walking up an inclined board held up by the ground on one ...
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5answers
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Moment of Inertia, why $r^2$and not $r$?

So my engineering mechanics book includes a brief discussion on area moments of inertia. Unfortunately, the ensuing chapter is predominately computational in nature. I don't have a thorough grasp of ...
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2answers
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Hanging a brick free over an edge by stacking them

National Geographics TV has a series called "None of the above". In one episode the presenter shows that by stacking 4 bricks (here shown as 'xxxxxxxx') you can have one of the bricks completely hang ...
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1answer
265 views

Stacking Shelves with Overhang

I want to stack some boxes which are 14" x 10" with some 12" records inside. This means that there will be a 2" overhang outside of each box. I know that to have an item to balance on a edge 50% of ...
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1answer
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Why do we consider the tension in a taut cable to be zero Newtons or Pound Force?

I have been browsing for a few hours now and I can't seem to find a reason for why this assumption is made for calculations and such in engineering problems like statics. It's a little embarrassing to ...
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2answers
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Why are clockwise and anticlockwise moments not balanced in this equilibrium scenario?

If we take moments about the peg, which is directly below centre of mass of the cone (which is $r$ cm from its circular base) we get $3rTcos(90-ø) = Trcos(90-ø)$. $T$ = tension in string. Clearly this ...
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1answer
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Why is the reaction between two hanging spheres by two strings the sine of the tension of the strings?

Two smooth uniform spheres of radius 4cm and mass 5kg are suspended from the same point A by light inextensible strings of length 8cm attached to their surfaces. There spheres hang in equilibrium, ...
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1answer
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Forces in a Pulley System. First year statics homework

So basically I don't understand why my solutions to this problem are wrong and I don't know how to calculate the normal force. If someone could explain why my answers are wrong and explain the normal ...
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1answer
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Calculate weight needed to balance a beam

I have found many sources to determine the weight or force needed for a balance moment, but not one that included the weight of the beam as a variable. I assume this is a very simple equation. Please ...
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1answer
169 views

How is this system in equilibrium? [closed]

So, after mathematically calculating the answer I found it to be zero. But my teacher says I don't have to do the calculation as this system is in equilibrium and the initial acceleration is zero. But ...
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2answers
584 views

Two sliding blocks and friction [closed]

I was doing a practice problem in prepping for a midterm and then numbers that I got just seem implausible. I know that they are the 'right' answers, I'm just not sure if this situation could exist in ...
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1answer
268 views

Static analysis of rigid bodies in 3D [closed]

How to calculate torque due to gravity of a 3D linkage mechanism? I am performing a static analysis of a Baxter Robot arm. How to calculate the torques at each of the joints ?
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Can this really happen?

I saw an interesting image , would it fall down or stay in stationary?
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3answers
455 views

Why exactly is the pressure an object experiences at a given depth in a fluid?

I am currently trying to work through why an object with smaller density than the fluid it is in floats upwards. I know that the object experiences pressure in all directions because it has moved ...
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6answers
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Which way will the scale tip? [duplicate]

This problem has bothered me for quite some time and I can't solve it. I have even tried to make a construction, but it sometimes tips to the left and sometimes tips to the right :). When we submerge ...
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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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3answers
296 views

How does torque work?

Why can we assume the the net torque is equal to zero when we pick one of the points as the axis of rotation. For example if we selected the left leg of the table for the axis of rotation why can we ...
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0answers
181 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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1answer
581 views

How to calculate the maximal weight that a cable can support? [closed]

Exercise: Exercise from Theory and Problems of Physics for Engineering and Science. In the crane here the boom is $3.2 \text{m}$ long and weighs $1200 \text{N}$. The cable can support a tension of ...
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0answers
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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 ...
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1answer
425 views

Basic Static Equilibrium of a rigid body

I'm trying to understand static equilibrium in 3-dimensions, but I feel like I should understand it in 2-dimensions first let's assume we have a rock with inhomogeneous density (black rectangle) with ...
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7answers
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Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table

I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. ...
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1answer
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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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1answer
617 views

How to make a free body diagram of a lever?

So this is what we are working with: Basically, the spring and the lever are used to press in the plug (part no 2). I need to find the force that is acting upon the welding (I painted it in red). Now ...
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1answer
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What is the difference between Quasi static and Dynamic simulation?

I'm a newbie in Physics, I read some papers in bio-mechanical that model human joint motion, some of them are modeled using Dynamic, while others using Quasi static. All I know so far is that in Quasi ...
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1answer
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Where does the formula for bending of a rod come from?

For a rod of length $l$, breadth $b$, depth $d$, and Young's modulus $Y$, the rod's center of mass comes down by a distance $\delta$ when a weight $W$ is hanged from its center $$\delta = \frac{Wl^3}...
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1answer
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Static geometry problem [closed]

Why is the force Nb has triangle of height a and base 2r. Why is not height 2r and base a?
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1answer
554 views

direction of resultant moment about axis using scalar and right hand grip rule? [closed]

From the picture posted, this question is taken from my solution manual. I understand that using vector method of finding the resultant moment. I also know when we use scalar with right grip rule to ...
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2answers
538 views

Why are truss members two force members and why are the forces directed along the axis of the member?

In Hibbeler's book, Engineering Mechanics: Statics, on pages 264-265 it is mentioned that two assumptions are made in the design of a truss: All loadings are applied at the joints The members ...
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1answer
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David Morin's question: Mountain climber [closed]

This question is from Introduction to Classical Mechanics, David Morin. A mountain climber wishes to climb up a frictionless conical mountain. He wants to do this by throwing a lasso (a rope with ...
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2answers
524 views

Rigid body equilibrium word problem

In my 100-level university physics course, we are just starting to touch on rigid bodies and tension. While I am fairly certain that I approached this the right way, I would appreciate if someone ...
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2answers
339 views

Forces on a ladder leaning against a box

My question is based on the following problem: A ladder of length $l=3\mathrm{m}$ is leaning against a box with height $h=2\mathrm{m}$ so that the angle between the ladder and the ground is 60 ...
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1answer
675 views

Problem regarding Buoyancy forces and Archimedes principle

A thin-walled container of mass $m$ floats vertically at the separation surface of the two liquids of density $ρ_1$ and $ρ_2$ . The whole mass of the container is concentrated in the part of height $...

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