# Questions tagged [moments]

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### What is the difference between torsional rigidity and torsional stiffness? Which would be better for comparing stiffness of two parts?

I am trying to compare the torsional stiffness of two injection moulded parts. I have applied torque to these parts and measured their resulting twist angle. I have plotted the data for both parts ...
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### Could moment be an imaginary concept?

In the figure above, a horizontal singular force is applied to a column from its end point. If we examine the column with the finite element method, we see that there are tensile and compressive ...
41 views

### Harmonic drive motor output bearing specifications and bearing arrangements

I'm not a mechanical engineer, but I've been tasked with designing a system that uses a harmonic drive motor (specifically, a LynxDrive). It must rotate a 200kg mass, which is heavily off-center. It ...
25 views

### Friction Clamp/Brake Conundrum

I'm trying to calculate the amount of torque I need to put into my braking mechanism in order to hold up a weight. The weight is 18kg at the end of a 170mm arm. this should result in an approx. 30Nm ...
49 views

1 vote
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### Why is there a negative sign in case of moments caused by longitudinal stresses?

I came across the following relations in the plate theory. I, however, don’t understand the reason for the negative signs in Mx and My. There is, however, no negative sign in Mxy. I am guessing, this ...
1 vote
177 views

### Horizontal "pinching" force of an arch with applied moment

I have some Shape Memory Alloy wire programmed to curl from a straight beam into a circle. The force this generates is approximated as a uniform distributed bending moment along the length of the wire....
61 views

### Max bending moment estimate

Context: I study aerodynamics and want to design and build an RC wing to put the theory I learned into practice. The essence of the theory I learned is: Given some mass of wing building material, how ...
1 vote
239 views

### Torque calculation for DIY friction wheel drive electric unicycle

I’m building a friction wheel drive electric Unicycle. Something like this; My question is how much torque should the friction wheel drive motor have considering the total mass of unicycle including ...
25 views

### Are you able to compute the bending moment exerted on the inner edges of parallelepiped box under inner pressure?

Suppose you have a parallelepiped box of dimensions $a\times b\times L$ with $L\gg (a+b)$, filled with simple distilled water exerting a uniform and constant inner pressure $p$ as reported in figure. ...
6k views

### What is the difference between mass moment of inertia and area moment of inertia? And why mass moment of inertia alone used for kinetic rotation?

What is the difference between mass moment of inertia and area moment of inertia and why mass moment of inertia alone used for kinetic rotation? Is there a possibility to use them interchangeably?
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### Moment of a force

How come when I try using the formula M = rF (sintheta) I get Moment at D = .223 * 300 * sin(25)= 28.4 Nm but it's wrong. The answer uses cross product but I thought I could just use the magnitudes ...
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### Is there a way to solve this complex statics problem algebraically?

This problem can be solve in 2 ways either I solve it with vectors which would be relatively painful and more time consuming and the other faster way is algebraically but I faced a problem when trying ...
430 views

### Torque for servos of tiltrotors

I am sourcing a servo for a tiltrotor drone and need to calculate the required torque to rotate the propeller and the motor from facing the front to facing the top. I understand that the minimum ...
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### How to calculate the moment of inertia of a propeller

I am trying to design a VTOL system that uses a servo to rotate a propeller and the attached motor so that it can provide thrust when it is at 0 degree and lift when it is at 90 degree. However, I ...
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1k views

### Understand how to choose the pivot point to calculate the moment of forces in dynamics

In statics, the net force and the net torque must be both zero. The net torque is the vector sum of all the involved torques (first moment of each force) about any arbitrary point $P$. The point $P$ ...
323 views

### How do you simplify this load diagram?

Very rough sketch but I'm having trouble with a Shear and Bending Moment problem, and I'm pretty new to the topic. This is the original diagram: I already simplified the left side (not sure if it's ...
1 vote
2k views

### Which force generates the reaction moment in a fixed support

The question is: Which force causes the reaction moment at a fixed joint ? Lets consider a very simple example, a beam with one end connected by a fixed support to a wall. I understand that at A, ...
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### Calculation of torque at the base

Hope you all are doing good. Can anyone please guide me on how to calculate the different torques at the base as shown in the image? Thank you for your time and help.
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### Is bending moment along a beam independent of the cross sectional area of the beam?

We know this that if the a cantilever beam (of any cross section) is fixed at one end and a transverse force is applied on the other, then it will bend. However, we just casually assume that the ...
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### What will be the force F for the given brake system?

I am getting two ways to find F. One is Fx0.2=30 Nm which gives F=150N Other is Fx0.2-640x0.13=0 which gives F=416N I am confused which one is incorrect. I know problem is too basic but still not ...
808 views

### Find the maximum stress at a point in a machine member

A machine member having a diameter of 50 mm and a length of 250 mm is supported at one end as a cantilever subjected to different forces as shown in the figure. Find the maximum stress at points A and ...
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1 vote
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### Does the turboprop engine torque get transferred to the engine mount and ultimately aircraft when engine is active?

When the turboprop engine is active, the propeller shaft rotates and causes the propeller to rotate as well, which in turn generates thrust. The propeller shaft rotates because of the torque (or ...
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1 vote
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### How to find the reaction at the pinned support A as shown in the picture? [closed]

Please help me solve the problem. I need to know the reactions at A for both the cases as shown. Please note that E is a roller, D is a pin support , B is an internal hinge and A for case 2 is a fixed ...
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### Lumber dimensions for machinery ramp

I would love help if anyone is able to offer any. I need to make a ramp to move equipment down a 3.5’ retaining wall. The ramp is to be 12’ long. I was going to use two 6” x 6” beams of Douglas fir, ...
545 views

I'm going to experiment with a parallel beam load cell like this one: https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/TAL220M4M5Update.pdf. I've read somewhere that for a setup shown on this ...
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1 vote
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### Unusual bending moment at simply supported beam in etabs [closed]

The horizontal beam is simply supported. I have assigned pinned to released the moment at the both ends. However, there's moment spike near the end in ETABS, what's the problem ? I have checked thru ...
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1 vote
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### What is the difference between a sum of moments about a point versus the moment at a point?

In class we're learning about moments, and I'm not entirely sure what is the difference between using an equation of equilibrium for the moments about a point (in this case C), and the actual moment ...
140 views

### How do I draw moments on hinged gates?

Hello I had a quick question regarding moments on hinged gates on submerged curves. Is there a general rule that we follow when we draw moments on hinges, do we draw the hinges in the direction the ...
3k views

### How do you calculate the shear force on the screws that connect a door to a jamb via hinges

I'm trying to calculate the shear forces on hinge screws or bolts. Here is a schematic of the door with the relevant values: First, I took a free body diagram of the door and its hinges. The ...
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1 vote
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### How does the diameter of a worm gear affect the amount of force needed to turn it

Can anyone help inform a discussion I'm having with fellow modellers on a model railway forum? I have a locomotive powered by an electric motor turning a 20mm diameter worm gear meshing with a spur ...
183 views

### Machine Analysis Problem: Finding the vertical force at joint K

Help me in determining the right solution in this problem. I already have an initial solution here but when I compute, my answer does not match to the answer key. I would like to know where did I ...
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### Diagrams of forces and moments of a statically determinate structure

I'm having difficulties with calculating the distribution of forces and moments in a statically determinate structure shown below. I'm especially confused about the arc part. Will there be only ...
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### BMD of the beam joined at intersection

4 beams are supported by the column at one side, another side is jointed together at the intersection. I have assigned UDL of 20 kN/m on all the beams. 2 beams are longer (3m), 2 beams are shorter (2m)...
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