# 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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689 views

### Proof of the Law of the Lever

Is there an accepted proof of the Law of the Lever? I know of several attempted proofs, such as Archimedes's, but these either are incomplete or do not transfer to the setting of Newton's Laws. (It ...
29 views

### Wrong application of principle of virtual work [closed]

My friend sent me a mechanics problem : 4 rigid rods, each of length $L$ and mass $m$, are jointed to form a rhombus-shaped frame which is suspended from the ceiling at one of the joints. A spring of ...
17 views

### In the figure, the force F in the system at point A Find the moment it creates [closed]

In the figure, the force F in the system at point A Find the moment it creates.
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### Conditions for equilibrium on a hexagonal pencil [closed]

A hexagonal pencil lies on a slope with inclination angle α; the angle between the pencil’s axis and the line of intersection of the slope and the horizontal is φ. Under what condition will the pencil ...
123 views

### Physical meaning of internal bending moment

Here's the setup: The textbook, where this is from, first walks through how to find the strain and stress as a function of z, which is fairly straightforward. Then, it calculates the "total internal ...
121 views

### Stability of a falling object

Suppose there is a falling object that has flaps around it providing resistance to the non-contact force of gravity. How would the vehicle theoretically not flip over? From my understanding, the ...
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### Mechanical Advantage of Static Double Pulleys

For a set of two double pulleys, the force acting on each should be equal to the tension in the rope times the number of ropes connected to the individual pulley if I understand correctly. In this ...
47 views

### Does an elastic massy hanging chain take the shape of a parabola?

This is a problem in "Differential Equations: A Modern Approach with Wavelets" by Krantz: If the length of any small portion of an elastic cable of uniform density is proportional to the ...
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### Shortcut to a problem based on toppling using D'Alemberts Principle [duplicate]

I found this question on this very site and was curious on how to solve it using D'Alembert's Principle Here's the link to OP(link) .I already know how to do it by balancing the torque about toppling ...
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### Strength of wall regarding a system of hanging mass

When we assume that mass m is directly at the center of L, and $\alpha$ is the angle between the rope and the horizontal, I am able to show that for equilibrium, $$\sin{\alpha}=\frac{m}{2M}$$ There is ...
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### An equation related to lever

To balance a lever, as we know, fulfills $f_1l_1=f_2l_2$, what is the condition that fulfills both $f_1l_1=f_2l_2$ and $f_1+l_1=f_2+l_2$?
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### Horizontal tension in hanging rope with mass [closed]

If we have a hanging rope with mass so that it forms a catenary, from what I have read, the horizontal tension in the rope remains constant. I also have seen that the equation of a catenary depends on ...
111 views

### Can you calculate the force of chair legs on floor?

I have kinda formalistic question. Eg. we have normal symmetric chair with 4 legs, and mass $M$. Can we calculate forces of chair legs on floor surface $F_1,F_2,F_3,F_4$ with only this data and why ...
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### Geometry of deformation of Axial members connected to a rotating rigid element

On axial members connected to a rotating rigid element, we have the following relationship $$\frac{-\delta_1}{a}=\frac{\delta_2}{b},$$ which is based on the concept of similar triangles. In the ...
46 views

### Tension in Common Catenary

I was reading the intrinsic equation of common catenary , where the author assumes tension in the catenary and proceeds. Why does a freely hanging rope with uniform mass per unit length has tension ? ...
688 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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### Force couple simplification

How is it possible to add all the force components to find resultant when forces are acting at different points on the body?
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### Position of resultant of two like parallel forces

I am solving Statics and stuck in middle of a trivial understanding. Let us say we have two like parallel forces acting on a rigid body . Force P has point of application as A and Force Q has point of ...
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### 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 ...
51 views

### Expression for force of gravity on an arbitrary curve with endpoints fixed

Consider the following problem: A frictionless tube lies in the vertical plane and is in the shape of a function that has its endpoints at the same height but is otherwise arbitrary. A chain with ...
128 views

### Measurement of force (statics) [closed]

body 1 and 2 are pulling the balance by 20 N what does the balance read? same question but without 2. for 1st question I thought the balance will read zero force because they are two opposite forces ...
51 views

### Question on statics

Consider a uniform beam that is supported by 3 pivots that are the same distance from each other (shown below). What will the normal force exerted by each pivot be? The situation seemed rather ...
321 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 ...
5k views

### Calculating torque in 3D?

Say you have a sphere, and you have several torque vectors acting on it, all at different points. Say you have the vector (6i + 3j + 5k) originating from point A, and the vector (3i + 1j + 9k) ...
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### Static equilibrium problem [closed]

I am designing a balanced-arm lamp structure for a robotics project and I obviously want the lamp to stay on its base without falling when the arm is extended. For that, I applied the conditions for ...
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### Resolution of forces (vector components) to find the resultant force [closed]

I'm a CAIE AS-Level student and I'm having a bit of problem with a physics question. It goes like this, An object X rests on a smooth horizontal surface. Two horizontal forces act on X as shown in ...
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### Varignon's theorem (Principle of moments) failure?

Varignon's theorem states that "If many coplanar forces are acting on a body, then the algebraic sum of torques of all the forces about a point in the plane of the forces is equal to the torque of ...
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### How come at a certain joint a truss is a zero force member and at another is isn't?

I have a slight confusion regarding zero force members. I'm analyzing a structure and I started at joint E and found that truss GE has a force of 8.4 [kN]. However, if I analyzed it at joint G, I can ...
1k views

### Influence of couple-moment's position on bending moment diagram

The moment of two equally opposing force would create a couple-moment. Since the couple-moment value is invariant to the point considered to calculate the couple-moment, I can replace the two equally ...
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### Hooke’s Law and Energy

I have a quite a simple question that is escaping me right now. The work done on any body is just the net force multiplied by the distance the force acts on it for. For example: the work being done on ...
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### Is it possible to create negative ions without ionization?

I read that the air purifiers that can create negative ions also increase ionization, in theory is it possible to create a negative charge/ negative ions without creation ionization similar to ...
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### 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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### How to find the loads of the four posts of a deck?

For a square deck of length 1 and neglectable weight, if it has to hold a heavy weight of mass M at (x, y), what is the support force of the four posts at the corner? The forces are $F_{00}$, $F_{10}$...
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### 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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### How do I calculate the effort force exerted by my hands while holding a high plank? [closed]

This high plank is an example of a 2nd class lever. The fulcrum is at the feet, the load is at the centre of gravity of the body, and the effort is at the hands. If I know: My weight (the load force)....
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This are eccentrically loaded bolts in which the plane of loading is parallel to the bolt plane.When deriving an equation to this particular problem almost all books start by assuming that \frac{F_{...
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### Using preload to resist bending moment on an unfixed cantilever beam

I have a cantilever beam that is resting against a wall (not fixed) and will not slide (strictly looking at bending moments). The beam of length = 0.3m is under a distributed load of 4000N and a ...
376 views

### Moment of force about a point definition

In defining the moment of a force about a point as "the tendency of one or more applied forces to rotate an object about an axis [going through a point, hence also about a point]", I see it logical to ...
57 views

### How do we account for the non-net accelerations for forces in static systems?

I've googled the heck out this (as a non-physicist) and found a ton of similar questions answered but did not find anything that made the light bulb go on. I don't think I'm a crank, so here it goes. ...
51 views

### Pulling force required to get stationary vehicle moving

Background There are many examples from humans pulling heavy vehicles, ranging from trucks to airliners. When researching the physics behind this, most results pointed to the reduced rolling ...
2k views

### How to know what method to use when finding resultant forces?

I am quite confused as to what method should be used when finding resultant forces. Here are two examples of a question that asks to find the resultant force. One requires the parallelogram law to ...
3k views

### 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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### Pressure of rubber band on cylinder taking friction into account

Suppose I have stretched a rubber band around a cylinder of radius $R$ such that the rubber band is under tension $T$. My understanding is that in the ideal situation, with no friction, the band ...
83 views

### The Leaning Tower of Pisa [closed]

Can we calculate the time when the Tower will lean to the extreme point that its center of mass will be out of its balance...?
336 views

### Conceptual Question about Suspension Bridge Forces

Two walkways are suspended from vertical rods. In the first scenario, one long rod supports both walkways and is attached to the ceiling. In the second scenario, two shorter rods are attached to each ...
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### What is the physics explanation for why an object with a larger base is more “stable” or and more able to “balance”?

What is the physics explanation for why an object with a larger base is more "stable" or more able to "balance"? For example - two pyramids, one on its tip (less stable) VS one on ...
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### Water column's pressure canceling out problem and it's microscopic point of view

If you see my horrible reference picture, you will see that the U shaped tube is placed inside the field where gravitational force exist. And the bottom of the tube is opened, tube is filled with ...
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### Why the dust on the wing cannot be cleaned by air flow? [duplicate]

I recently saw that the dust on the airplane's wings are frequently cleaned by some human workers (generally after every trip, workers clean the fine dust on wing's surface by hands). But I have a ...