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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
27 views

Reaction Forces of 2D pin jointed truss [on hold]

How do i find the reaction forces of the 2D pin jointed framework (see picture attached)?
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0answers
51 views

What is the deep “physical” intiutive meaning of torque? [duplicate]

There is a rule that $$lever\;arm(1)\times force(1)=lever\;arm(2)\times force (2)$$ This is because the torque equivalence principle. I am only talking about vertical forces (so cross products' mods ...
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1answer
39 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 ...
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0answers
14 views

How to get moment's vector from its magnitude?

For force multiplying the unit vector x force magnitude ,But I can't figure out what to do for moments(moments in 3D system with required coordinates)
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0answers
14 views

Confusion on Independance of Forces [duplicate]

If a perpendicular force is indepedent and unaffected by one another. Why is it harder to move larger/heavier objects, thus slowing the speed of the object. Isn't these two forces (horizontal & ...
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votes
1answer
37 views

Friction & Gravity Relation [duplicate]

Imagine a flat horizontal road surface(made of the same material), the first road is placed on earth, the second one is placed on the moon. 2 cars are placed on both roads and start moving, would the ...
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0answers
16 views

Equilibrium of Rigid Bodies [closed]

Hi! I'm would like to know the explanation on the answer in this particular problem. I really did not understand why did he make the force concentrated on the middle.
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2answers
27 views

Is the method of joints only applicable to trusses?

I am confused as to whether the method of joints is only restrained to pin-jointed trusses or it can be applied to other statics problem, for example the one shown in the picture, and why?.
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2answers
44 views

Tangential Contact forces between objects

My book says that there are two forces two objects experience when they're in contact with eachother. (it uses an example of a cylinder and a parallelepiped that are in contact with eachother) The ...
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2answers
65 views

How would I draw the forces on two identical ladders propped up against each other, connected by a rope?

Two ladders of uniform density and equal mass m are propped up against each other at angles $\theta$ from the frictionless ground. A rope of tension $T$ connects the two horizontally a distance $\...
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1answer
26 views

Statics problem: Finding resultant force angle measured from positive x-axis

I have this diagram: And I have done these calculations: $$R_x=-20sin(30)+30cos(35)+80cos(45)=71.14 \; lb$$ $$R_y=20cos(30)+30sin(35)-80sin(45)=-22.04 \; lb$$ The magnitude of this resultant force is ...
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2answers
40 views

From Where Did The Table Get Energy? [duplicate]

When a block in resting on a table (the table is on Earth) the table stops the block from going more down, from where does it get the energy to apply a force opposite to gravity?
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2answers
77 views

Beam attached to a wall

Suppose I have a rigid beam attached to a wall, how can the reaction force on the point the beam is attached to generate a static equilibrium on the beam? ...
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1answer
41 views

Virtual work - Tension in a string

I am confused about the way Tension or Thrust is used in equation of virtual work. I mean whether to use $ T\cdot dr$ or $-T\cdot dr$ (work done by tension). For instance in the below case : A ...
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1answer
84 views

Ladder and friction (wall and floor) [closed]

Here there is a problem and the proposed solution: UPDATE: I can't understand why getting the maximum friction to solve this kind of problem when it is known that static friction, depending on other ...
1
vote
2answers
54 views

What is the maximum force you can exert on the ground with one leg? [duplicate]

You are standing on hard floor. Clothes weigh negligibly. You move only your leg. Everything else remains stationary. Assume you are made of the same material as the average human. Can the force ...
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0answers
41 views

Base length and Mass required to stabilize a large heavy sign [closed]

I have an 8ft x 7.5ft sign that is about 4inches thick and weighs about 150lbs. We can assume the whole thing is made of the same density I am building the stand for this and I cannot anchor it to ...
2
votes
1answer
47 views

Is there a name for this phenomenon?

Imagine I have a cylindrical pipe closed on both ends with lids. I fill it with sand and compress the sand tightly. Now I hold the cylinder vertically and remove the bottom lid. The sand will counter ...
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1answer
47 views

Tipping angle of a box

how do you calculate the tipping angle of a box? That is the maximum angle a which a box can reach before tipping over. help, please!
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4answers
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Why is the shape of a hanging chain not a “V”?

From Wikipedia: To answer this question: "What is the shape of a chain suspended at both ends?" we can use the variational principle that the shape must minimize the gravitational potential energy. ...
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1answer
298 views

3 people carry a log of wood, which one is carrying the most weight [closed]

I saw this on a youtube video. The answer is that the one in the middle is carrying 25 % more than the other two. Can someone explain this?
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1answer
102 views

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 ...
1
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1answer
50 views

A question about temperature in the concept of a macroscopic statistical-mechanical system

I recently have come across a question while working on Statistical Mechanics. The question itself was quite straight forward (no this is not a "do my homework" question in case you were wondering) ...
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2answers
51 views

Power in 1st Gear

The max power an engine puts out is what determines the max speed a car travel at right, obviously it's more nuanced than that because there are losses in the drive train, and the shape of the car ...
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2answers
67 views

Finding the equation of a chain hanging between two points

Say I have a connected at either end to two points, $A(x_A, y_A)$ and $B(x_B, y_B)$ of length $l$, where $l \leq \sqrt{(x_B - x_A)^2 + (y_B - y_A)^2}$, how would I go about finding an equation of its ...
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vote
1answer
73 views

Conditions for Static Equilibrium of Rigid Body [duplicate]

When there are forces acting on a rigid body, the two conditions that has to be satisfied for the body to be in static equilibrium are: 1. The sum of all forces must be zero (translational equilibirum)...
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1answer
136 views

Work done in lifting a object from underwater if it displaces $W'$ of water? [closed]

A spherical shot of W gm weight and radius r cm, lies at the bottom of cylindrical bucket of radius R cm. The bucket is filled with water up to a depth of $h\,\mathrm{cm}$ $\left(h > 2r\right).$ ...
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1answer
97 views

Why can't a pyramid stay balanced on a vertex? [duplicate]

A pyramid, such as a tetrahedron/3-simplex, or any other isohedron, falls from some height and lands on a vertex. It will eventually end up with a face to the ground. Why can't it stay balanced on a ...
2
votes
2answers
63 views

balancing a weight on a table without tipping over

I have a statics problem. Here is a model for a table: a circle of radius 1.5 ft a pole in the center a base in the shape of an X. I place a weight on the table on the edge. How much weight can ...
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1answer
36 views

Equation to model change in leverage point

Is there a mathematical model for the situation below? First, I want to know how much force I would need to lift this block some distance using this wooden board. The block is situated against a wall ...
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0answers
52 views

How do bicycle pedal forces resolve?

If you're standing on a stationary bicycle, with pedals at 3 and 9 o'clock, how do the forces resolve if you shift your weight over the rear pedal? Most weight is on your back foot. Since your front ...
0
votes
1answer
170 views

Static equilibrium- when do you use forces and when do you use torques?

I'm working on an answered physics question in the book but I'm having trouble understanding why the problem could be solved by setting net torque equal to 0 and not net force. You are asked to find ...
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1answer
33 views

Rotating a cube to the verge of tipping over [closed]

The problem: A $100\,\mathrm{kg}$ cubical box lies on the floor. A child pushes horizontally at the top edge. What is the magnitude of force to put the box on the verge of tipping over, given that ...
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0answers
15 views

How does a balancing machine works? [duplicate]

Suppose I have a balance . Both of its pans have same mass kept on them and it is balanced with both masses at same height . I pull down one of them to some height. Will it come to its original ...
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1answer
33 views

How to solve problem with homogenous ball at equilibrium? [closed]

The answer according to solution manual: $F_A=566N F_B=283N$ I am not asking for you to solve this exercise, this is not a place for homework, I know. I need help how to think so I can solve this ...
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1answer
38 views

Does a car effectively become heavier the faster it moves?

Just for clarity, I'm not asking in relativistic terms. Assuming the engine's pistons aren't horizontally opposed, would the vertical force of the pistons move the car downward? Or would it not ...
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1answer
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0answers
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What stresses should be considered to determine the effective stress and FOS?

This question I tried to solve by considering the torsional shear and transverse shear and axial loading. But the answer is not clear. But the answers that I got by different trial and error method ...
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1answer
39 views

Why exactly do two parallel equal magnitude forces acting on a rigid body produce no rotational motion?

How exactly do we justify that two parallel forces $\vec{\mathbf{F}}_1$ and $\vec{\mathbf{F}}_{2}$ having the same magnitude, acting on a rigid body, do not produce a moment? Yes, if we consider any ...
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2answers
44 views

Can we take rotational equilibrium of only one part of a body?

Can we take rotational equilibrium of only one part of a body? Such as in a step ladder, where BD is a rope. Can we take rotational equilibrium of AC about C, and not the full ladder?
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2answers
304 views

How does a balancing toy work?

I know that the balancing toys have their center of mass under the axis on which they are balancing. That's why they stay still. But when we give a little tap on it, it re-balance itself. But how does ...
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3answers
2k views

What holds up the lowest point of a rope following a catenary curve?

A catenary curve is the curve followed by a rope suspended at both ends in uniform gravity. I thought I would try to solve it myself because it seemed like a good challenge, but almost immediately I ...
0
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1answer
323 views

Why frictionless joints are assumed in pin-joint truss analysis?

In pin-jointed truss analysis, we consider some assumptions. One of them is that they have friction-less joints. Why do we have this assumption? What would happen if the joints were to have ...
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3answers
104 views

How is weight distributed in a stack of boxes? [duplicate]

Consider the following stacks of 2D boxes with uniform density: ...
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2answers
237 views

Why is the horizontal component of the reaction force at one of the hinges (which has a rounded bottom) neglected?

In the textbook "Engineering Mechanics: Statics (7th edition)" by James L. Meriam and‎ L. G. Kraige, Chapter 3: Equilibrium, in the section titled: "Examples of Free Body Diagrams", I found an example ...
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1answer
52 views

Is this system statically indeterminate?

In the static configuration of rectangular blocks shown below, we will assume that the gravitational force acting on each block is $1$. Each also has uniform density. We will also assume that: $(x_1,...
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3answers
50 views

Weight of objects

I recently observed that on a weighing machine(rectangular) a object weighed the same as the half portion of the same object with it's other half hanging out of the boundary of the machine (The ...
0
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1answer
257 views

Friction between ladder and wall (statics)

I was given the following task: My problem is the following: For $A$ and $B$ I’ve got friction forces $R_A$ and $R_B$. I can calculate those by using the formula: $R_A = N_A \cdot \mu $ $\mu $ is ...
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1answer
58 views

Force-couple system equivalence: 3 moment equations

In force-couple system equivalence, We can show that two systems are equivalent if the resultant force in both are equal and that it has the same line of action. So Rx1 = Rx2, Ry1= Ry2, Ma1 = Ma2 ...
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2answers
148 views

Static Equilibrium: Normal Force

Consider the following situation where an object (for example a person) is at rest at point D such that the system is in static equilibrium: Why is there no normal force present at point D? To my ...