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1answer
27 views

Mechanics, Centre of Mass Concept Question, why do objects topple on an incline?

Mathematically, I understand how to approach a question and to figure out if the object will topple over on an incline. I just want to understand why is it when the object's centre of mass is no ...
0
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3answers
49 views

What does the “moment” in the moment of force or the moment of inertia refer to? [duplicate]

According to the Merriam Webster dictionary: Moment - a very short period of time Does the word "moment" in quantities like the moment of force or moment of inertia refer to this colloquial ...
3
votes
1answer
298 views

What is the meaning of “moment”?

What is the meaning of moment? I'm little confused about the word as there are some terms like moment of momentum, moment of mass, moment of force, etc. I want to know what exactly is meant by the ...
1
vote
1answer
32 views

Center of mass/centroid changes between 2d and 3d?

Unless I completely botched the calculation, I noticed something strange: if you find the centroid of a 2d curve, and then revolve the curve around its axis then find the center of mass, the CM is ...
3
votes
2answers
62 views

Force distribution on corner supported plane [closed]

This question has been annoying me for a while. If you have a completely ridged rectangular plate of width and height x and y that is supported on each corner (A,B,C,D) and has force (F) directly in ...
1
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1answer
40 views

Scientific definitions of “moment (of)” and “instant”? [closed]

What are the scientific definitions of "moment (of time)" and "instant"? Are they different with their definitions in everyday language? I also don't know the definitions in everyday language, of ...
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votes
4answers
188 views

Why does Torque exist?

Specifically, why does force increase with the moment arm? What about making a perpendicular force farther away from the axis of rotation increases it? How does the moment arm cause that?
1
vote
2answers
100 views

Forces on wheels in an accelerating vehicle

Assume that a motorcycle of mass $m$ has two wheels that are equidistant from its centre i.e the force on each wheel is $mg/2$. If the motorcycle accelerates forward, will the two forces on each ...
0
votes
1answer
37 views

Clarification on what inertia and area moments?

This is something I have never understood despite applying the formulas in many classes. What I'm hoping to find here is some clarification. My understanding is that the first moment of inertia is ...
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3answers
321 views

How can a bowling ball curve in both directions?

There is a popular video on facebook that I just don't understand. A man spins a bowling ball very fast then slightly taps it down the lane. Somehow it does half of a figure eight, curving around two ...
1
vote
1answer
292 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 ...
1
vote
1answer
46 views

Four bar linkage moment transmission

The question is. I know the angular velocity of $d$ after applying dynamic mechanics and the constant angular velocity of $b$ of $2\pi\ \text{rad/s}$ and I know the input moment of the power source ...
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vote
2answers
51 views

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. ...
-1
votes
1answer
68 views

What is a moment/torque?

What is a moment/torque? i know the formulas m = fxd (Nm), I know how it works, what is does etc. But think of it fundamentally, how is it possible, that a force becomes greater when the arm of an ...
0
votes
0answers
26 views

Bending moment in composite beam with internal “active” stress

I am looking at a problem of a bending composite beam with a symmetric cross -section, $A(s)$. Above the neutral axis $s$ is material $U$ and below the neutral axis is material $L$. $U$ has an ...
0
votes
1answer
48 views

How can I work out tensions using moments? [closed]

If you were given the weight of a metre rule, its weight and the distance between 2 vertical rods holding it up, how would you work out the tension in the rods using the concept of moments or vectors? ...
0
votes
1answer
48 views

Finding the coefficient of friciton [closed]

I'm asked to find the coefficient of friction before the bar starts sliding. Here is my solution -> ∑M = 0 -mg * 1.4863 + 1.8159*T = 0 (T*1.8159) i found by using a cross product ( -2.9726i+ ...
0
votes
1answer
30 views

Finding the friction before slipping [closed]

There is a string that is attached to a bar as shown below in the picture. What is the coefficient friction between the bar and floor before bar starts slipping. I have chosen a pivot point about ...
0
votes
2answers
211 views

Need help understanding angular acceleration due to gravity

The question asks what the angular acceleration of an uniform disc of radius $R$ rotating about an axis passing through its edge if it is released from rest with its center of mass at the same height ...
0
votes
1answer
180 views

Why are inclined push-ups harder?

I came up with a random question which looked simple, but I can't work out the answer. The question is, why are inclined push-ups harder? And by inclined push-ups I mean push-ups with your legs on a ...
0
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0answers
92 views

Moment of Inertia of a Motion Simulator Frame

I have a rather specific question. I'm trying to build a motion simulator for flight and racing sims, similar to this: https://www.youtube.com/watch?v=JQAZB3EnI_w . The basic concept is a platform ...
0
votes
3answers
52 views

Multi-Force Lift

Background: I am creating a 3D game. A ship has 3 thrusters that apply force up (Z+) to counteract the force of gravity (Z-). I am trying to figure out how much thrust to apply to each thruster to ...
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votes
1answer
37 views

Why can't we have more than 3 moment equations in equilibrium equations

Excuse me for a kind of stupid question but, In statics of a 3D rigid body, the equations to determine equilibrium are at most 6 (Fx Fy Fz Mx My Mz = 0) (not counting those from hinges and rollers). ...
0
votes
1answer
154 views

Moments and forces, when part of the scenario involves a circle or arc rather than a straight line

Some questions below, involving strategies, regarding the following problem: A hoop of weight $20$ Newtons can rotate freely about a pin fixed in a wall. A string has one end attached to a pin, ...
0
votes
1answer
93 views

Resultant center of rotation due to multiple moments

Say, there are multiple moments (M1, M2, M3) acting on a body (of irregular shape) at points P1, P2, P3 respectively. The body is free to rotate about any point. Now, which resultant center (the ...
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votes
2answers
75 views

How is electric dipole moment analogous to mechanical moment?

Diplole moment is q*2l. I don't understand the similarity between dipole moment and ordinary mecanical moment.
0
votes
1answer
64 views

Bending moments when lifting houses

I have a 3km-wide square with a tower in each corner (A,B,C,D). On edges AB and CD there are level rigid massless beams supported by the towers. A third beam lies on these two, parallel to BC (i.e. ...
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2answers
100 views

Wheelie physics part 2

Okay, so I got some really great advice from the community here but I am still hung up on some conceptual problems. I posted earlier trying to determine the axis that a bicycle rotates about when ...
3
votes
2answers
878 views

How does a wheelie work?

So I've been trying to create a mathematical model for an electric motorcycle and began to wonder about the maximum possible torque that could be supplied to the rear driven wheel without having the ...
-1
votes
1answer
44 views

What does $\bar{x}_{\textrm{el}}$ represent?

In the context of centroids and moments, what do $\bar{x}_{\textrm{el}}$ and $\bar{y}_{\textrm{el}}$ represent? For example: $$\bar{x}L = \int \bar{x}_{\textrm{el}}dL$$ Some references that use ...
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2answers
75 views

Need derivation of a formula related to determination of moments of a object about $x$-axis and $y$-axis

I'm given a plate,its density $\rho$ and it is the region bounded by the two curves and on the interval [a,b].I want to find the center of mass of the region below. I’ll first need the mass of ...
0
votes
1answer
459 views

Calculate reaction forces, bending moments and shear forces, udl=0.5kN/m

i have reaction forces of Ra $= 7.890625N$ & Rb $=1 03.359375N$ my shear force calculation equates to 0N at 5.5m which i believe is correct however i am having trouble getting the bending ...
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votes
3answers
2k views

The momentum of a swinging sword

Suppose you are faced with a zombie, and the only way to kill it and save yourself is to chop its head off with your sword. However, you are very weak from illness, and can only afford to strike once. ...
2
votes
1answer
225 views

Torsional spring and Euler angles

I have a question about the moments generated by torsional springs. Consider an inertial reference frame A and a body fixed reference frame B. The frames are connected by 3 rotational springs acting ...
1
vote
1answer
153 views

Is the moment-curvature relation for an elastic beam general?

The relationship between the moment and the curvature for an elastic beam is $$M = -EI\kappa$$ Previously, I have only used this with small deflections in static calculations. I am currently working ...
0
votes
1answer
321 views

Downward force applied at center of see saw [closed]

If we are given the length of a see saw of negligible weight, and the weights and distances from the center of the two people on the ends of the see saw, how can we find the downward force being ...
0
votes
1answer
101 views

Determine reactance force of four load cells arranged in two dimensions

I have constructed a "force plate" to reconstruct the location (x,y) of a steady state contact point force f. The system consists of four fixed compression load cells L1, L2, L3, and L4 and a thick ...
3
votes
1answer
128 views

Moments of vibrating string

I have to calculate first 10 moments for vibrating string with damping, but I don't know how to do it. I read about moments and in definition they mention linear system $$x'=Ax+Bu, \qquad y=Cx$$ with ...
0
votes
1answer
2k views

Calculating Resultant Force and Torque

I'm working on a sandbox game that allows the player to build a spacecraft and attach thrusters in arbitrary locations on the hull of the spacecraft. The game is set completely in 2D. (I'm a ...
2
votes
0answers
62 views

Fractional-Order Moments

Commonly seen in physics(and statistics) are the concepts of moments of order zero(mass), one(center of mass), and two(moment of inertia). In statistics a third moment (referred to as skewness) also ...
0
votes
1answer
100 views

Centre of mass, integral

I was answering a question on proving the parallel axis thereom for angular momentum and came across this: $$\int Yy'dm=Y\int y' dm=0$$ Where the position of the center of mass of an object is given ...
-1
votes
1answer
840 views

How do I know which force to use in moments calculation?

I'm working on some Statics problem, with the method of joints, etc and for all of them, we use sum of moments = 0. However, I'm very confused about which forces I should use to find the sum of ...
3
votes
0answers
352 views

Electrodynamic multipole expansion

I am reading Jackson, Classical Electrodynamics, and I have a question regarding the electrodynamic multipole expansion (with page numbers I refer to the 3rd edition). So on page 409, he gives in ...
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vote
0answers
97 views

How many padlocks required to make the Eiffel tower fall over?

Yes the title is an odd question, so I will provide a little background! Recently the sheer amount of padlocks on the Pont d'Art in Paris caused a part of its railing to fall off. Similar padlocks ...
4
votes
1answer
275 views

Why is a dipole moment called a dipole moment?

The General Formula for a moment is the following one: $$ \vec{M} = \vec{r} \times \vec{F}. $$ However the formula for a dipole moment is this one: $$ \vec{p} = Q \vec{d}. $$ How comes this is still ...
0
votes
1answer
86 views

Initial velocities of a collision [closed]

This is the question: A car of mass 900 kg and a van of mass 1300 kg collide at a crossroads. Investigation into the collision discloses that the car was travelling south east and that the van was ...
1
vote
2answers
843 views

Is the moment of a force the same about any point?

I know that when a body is is equilibrium There is zero resultant force in any direction, i.e. the sum of all the components of all the forces in any direction is zero The sum of the moments about ...
3
votes
3answers
582 views

Why does the moment of force (aka. torque) depend on the perpendicular distance?

Couyld anyone explain how the lecturer concluded that $$(\underline{r_2} - \underline{r_1}) \times \underline{H} = \underline{p} \times \underline{H}$$
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2answers
82 views

What will be the direction of the force required on the ball to move the ball up the stairs?

Is this diagram correct? The point of force A is at the farthest distance from the fixed centre O ,so the moment arm CD is greater and therefore,maximum torque would be produced.Is my concept ...
0
votes
2answers
1k views

Calculating axle load in cargo container (pics are included)

I'm current developing cargo loader software, but i have a little challenge with calculating load for each axle when a cargo is placed on container. I know that all axles will be affected (the nearest ...