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.

Filter by
Sorted by
Tagged with
1
vote
2answers
2k 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
votes
1answer
43 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 ...
2
votes
2answers
126 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 ...
8
votes
4answers
584 views

Newton's Third Law As Discussed in Den Hartog's Mechanics

A question, but some preliminaries in order to avoid answers involving concepts not yet introduced in the text I'm reading--Den Hartog's Mechanics. Near the very beginning of his book, Den Hartog ...
0
votes
1answer
976 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 ...
-1
votes
1answer
87 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 ...
0
votes
2answers
8k 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 "...
0
votes
1answer
122 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 ...
0
votes
1answer
44 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 ...
-1
votes
1answer
384 views

Lever Mechanical Advantage

In the attached image the force output of the plank is calculated to be the work done (FDf) divided by the height the block rises (Dw). So the force the plank applies on the block is (FDf)/(Dw). But ...
-2
votes
1answer
296 views
0
votes
0answers
12 views

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 ...
-1
votes
1answer
118 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 ...
-1
votes
2answers
109 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?
2
votes
1answer
863 views

Curvature of a cable supporting a suspension bridge in the regime where the mass of the cable is non-negligible

Assume I have a chain of uniform mass, $M_c$, suspended between two points such that it will follow the trajectory of a catenary curve when only supporting its own weight. Let's also say that this ...
0
votes
1answer
1k 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 ...
1
vote
2answers
5k 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 ...
1
vote
3answers
412 views

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

Consider the following stacks of 2D boxes with uniform density: ...
0
votes
2answers
514 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 ...
1
vote
1answer
72 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,...
0
votes
3answers
66 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
votes
1answer
535 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 ...
0
votes
1answer
109 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 ...
0
votes
1answer
140 views

Why is shear force indeterminate at a section where point load acts

Why is shear force indeterminate at a section where a point load acts, i understand it from the mathematical point of view, since the left and right hand limits would not agree and would lead to ...
1
vote
1answer
225 views

Tension exerted by strings at corners of a rope grid [closed]

I am a software developer and helping someone with an art installation. It consists of a grid made of ropes. Grid is $12 \cdot 12$ meter and internal squares are $1 \cdot 1$ meter. Grid is suspended ...
1
vote
3answers
454 views

Equilibrium of a rigid body

Why is it necessary for a body to have the net torque acting on it be balanced along with the forces for it to be in equilibrium? Isn't torque just some special case of force like rotation is a ...
2
votes
1answer
3k views

Estimate the reaction force on each leg of a 4-legged table

Assume you have a table with four legs with a weight placed somewhere inside the boundary created by the legs. The task is to determine the reaction force at each leg. Here are the problem ...
-1
votes
1answer
147 views

Statics: What it means if a rope snaps

There is a drawbridge that is held up by a hinge attached to a vertical wall on one side, and by a vertical rope on the other side. Say a horse starts walking from the wall towards the rope and at a ...
1
vote
0answers
121 views

Express $\tan{\theta}$ in terms of $\alpha$ and $\mu_s$ [closed]

Problem: Determine the least angle $\theta$ where equilibrium is possible. Express $\tan{\theta}$ in terms of $\alpha$ and $\mu_s$ Attempt: I started of with drawing out all the acting forces: ...
1
vote
0answers
56 views

Conservation of percent difference?

I was doing a lab to experimentally determine coefficients of static friction between two surface. This was the basic set up: The mass of the block is a known quantity. I was checking the maximum ...
0
votes
1answer
634 views

Maximum Load of a Crane before Car will Tip

Imagine a car with a crane. In scenario 1, the tension on the crane cable by the load points straight down, ie, perpendicular to the ground. In scenario 2, the tension on the crane cable by the ...
4
votes
3answers
1k views

A simple (?) problem of static equilibrium

A question on the site made me consider this simple problem, that unexpectedly seems to be indeterminate. Consider a perfectly rigid, homogeneous bridge of mass $m$ with three pillars, one placed ...
2
votes
0answers
211 views

Hard mechanics problem: Beam resting on three springs [closed]

I have trouble with following problem (ii): A uniform beam $AOB$, $O$ being the mid point of $AB$, mass M, rests on three identical vertical springs with stiffness constants $k_1$, $k_2$ and $...
-1
votes
1answer
332 views

Truss analysis how to calculate for a single beam?

Suppose I want to calculate the tension/compression force only in 4. Is there an easier way to calculate it or do I have to calculate everything with the joint method? I don't immediately see zero-...
2
votes
1answer
242 views

Why is shear stress equal to half of yield stress

Why is the value for acceptable shear stress equals to half of yield stress? $$ \tau = \frac{\sigma_{yield}}{2} $$ P.s Along the math behind it would be possible to explain this with visual consepts? ...
1
vote
2answers
104 views

What friction vector direction will be in this case?

Two bodies 1 (at the top) and 2 (the rightmost one) with same masses are connected to each other with lightweight non-expandable thread thrown over sheave. The block A has an acceleration a. I need to ...
1
vote
1answer
38 views

Is there a quick way to convert between two coordinate systems?

I am solving a few Statics problems that ask to find the resultant moment that a given force produces about a given axis. The problem has two sets of coordinate systems (x, y, z) and (x1, y1, z) where ...
-1
votes
1answer
81 views

Reliable, intuitive method for working out the direction of static friction?

I've seen Consistent method for finding direction of static friction which was the closest question I could find, but I'd like something better. I need a method which : 1) Intuitively makes sense 2)...
1
vote
1answer
21k views

Determine resultant couple moment by summing moments

The question states: Determine the resultant couple moment by (a) summing moments about point $O$ and (b) summing the moments about point $A$. I used scalar analysis for solving this ...
-2
votes
1answer
662 views

Why don't underground tunnels collapse on themselves?

I understand that underground tunnels don't collapse because the forces acting on it must be in equilibrium but I don't know which forces are present and I don't know how they are built.
0
votes
2answers
99 views

How does an Anti-tilt chair work?

These chairs are designed as per European Educational Standard Part 1 and 2. These are claimed by the manufacturer as Anti tilt, so basically it makes it relatively difficult for a child to fall when ...
5
votes
1answer
5k views

Forces and torques about the CENTER OF MASS of a physical pendulum

I'm currently stumped by the following situation. Say we've got a rectangular physical pendulum (think ruler with a hole-punch at one end). It's trivial to analyze the motion of the pendulum with the ...
-1
votes
1answer
238 views

Membrane shape under pressure

If I have a circular membrane that is fixed by the edges and then I apply a uniform pressure to the membrane (let's say the membrane is the top of a circular chamber that has a rigid wall and flat ...
-2
votes
1answer
230 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.
1
vote
1answer
3k 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 ...
0
votes
4answers
4k 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 ...
0
votes
2answers
2k 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 ...
0
votes
1answer
106 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 ...
2
votes
2answers
5k views

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 ...
0
votes
5answers
5k views

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 ...

1 2 3
4
5
10