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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3
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1answer
420 views

Distribution of normal force on a book resting on the edge of a table

Assume a uniform book is resting on a table. The book has length $1$. But not the entire book is resting on the table, a bit $\alpha$ is sticking out of the table. Obviously, due to experience, we ...
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1answer
95 views

Projection of force [closed]

So to find the projection along the cable in question 124 we used CA (not AC). Why? I thought that we always start from the end point of the Force, which is AC and not CA.
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1answer
141 views

How to deduce the following equilibrium equation?

I have seen the following free-body diagram in an engineering paper, J. Compos. Constr. 9, 388 (2005) (e-print): As it is mentioned in the paper $f_j$ is the stress in the FRP layer (which acts ...
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1answer
190 views

Forces on Bifolding Door with horizontal hinge

I'm a programmer who's been put in charge of some motor control problems and I need your help, so please forgive me if the question is silly. The problem in question (see inserted picture) is ...
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1answer
2k views

How to determine tipping point for a single pedestal dining table?

How to determine minimum weight to tip over a single pedestal dining table? We have a client who wants a rectangular table, 72" L x 42" W, and the MDF top will weigh approximately 100 lbs and the ...
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4answers
3k views

Determining tension in a rope between two masses using only force arrows (i.e. no calculations)

The situation sketched above is often used for problems involving tension. Let's say we know the masses $m$ and want to determine the tension $T$ in the rope (no friction, massless rope). Since ...
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3answers
469 views

Static friction free body diagram on a flat plane

Do you include static friction on a free body diagram for a static box on a flat surface? Or do you just include Force of gravity and Normal force? We know when the box is moving there is Frictional ...
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2answers
3k views

Distribution of weight of an inclined object

We have a rod, 1m long and negligible height compared to the length, mass 10Kg uniformly distributed (center of gravity in the center). It is tilted theta degrees to the horizontal, and rests on two ...
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2answers
801 views

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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1answer
98 views

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
174 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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1answer
51 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
168 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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1answer
82 views

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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3answers
105 views

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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1answer
104 views

Method of joints: The direction of forces

I have the following question: I need to find the load in truss element DF. I calculated the reaction forces at E and D. Fex = 360 KN Fy = 405 KN Then, I used the method of sections at point F ...
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3answers
1k views

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
241 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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0answers
87 views

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
313 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
115 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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1answer
759 views

Three hinged rods problem

This is an edited version (I added a solution and a physics concept related query) of a closed question that I'd like to see the answer to Three identical rods are connected by hinges to each other, ...
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1answer
1k views

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
422 views

Pressure of the same mass of fluids of different densities?

Suppose I have 2 fluids of different densities, and I pour the same mass of each fluid into 2 identical cups. I feel like I'm confusing myself here — on one hand hand, both cups contain the same mass ...
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2answers
201 views

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
163 views

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
629 views

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
2k views

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
142 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
473 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
227 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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2answers
72 views

Can this really happen?

I saw an interesting image , would it fall down or stay in stationary?
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3answers
305 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
181 views

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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3answers
250 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
152 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
446 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
31 views

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
400 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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3answers
438 views

Under what condition would I fall off a cantilever chair? [closed]

So this question is nagging at me and after many rounds of searching I still can't figure it out. I want to know is how load is distributed through a cantilever chair. Under what circumstances would a ...
37
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7answers
8k views

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
443 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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2answers
6k views

Why is skidding considered kinetic friction when braking on a car?

So according to my textbook applying the brakes hardly to essentially lock up the wheels causes skidding which is kinetic friction so the breaking distance is longer. However, if the brakes were "...
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1answer
1k views

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
992 views

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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2answers
6k views

Why are arc bridges stronger than flat bridges?

To keep the question brief: in bridge design, why is the arc structure favoured compared to a simple flat one? In other words, how does the curved platform alter the force decomposition of the load ...
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1answer
55 views

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
449 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 ...
3
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2answers
359 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 ...
4
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1answer
625 views

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 ...