# Calculating the Moment from a Different Vantage Point

• Tymofei
In summary, the coordinate system was located at the center of mass, but the results were different when the coordinate system was shifted to point 'A'.
Tymofei
Homework Statement
Dynamics
Relevant Equations
General moment eq
Summary:: Just a simple 3d rigid dynamics question which I am trying to solve by placing coordinat system differently from original solution.Everything looks ok but results are different.

Mod note: Post moved from technical section.
Thats my question.As you see coordinate system was located at center of mass.I just shifted it to point A and recalculated values.
Everything was same except Inertia about z and y-axis which was multiplied by 4.But at the same time moment effect coming from gravitational force was included to calculations so i thought they will cancel each other.But results was different than was mentioned on the original solution.
I know it looks nonsense trying to figure it when i already have solution but I am kind of obsessed .

By the way my values were:
My values for coordinate system placed at point 'A':

I_z = I_y = 6*10^-3 , I_x = I_xy = I_xz = I_yz = 0

Sum M_x = 0 = M_A_x

Sum M_y = 6*10^-3 * -12sin(theta)* -6*10^-3 * 12sin(theta) = -144* sin(theta)*10^-3 = M_A_y

Sum M_z = 6 * 10^-3 * 2 sin(2theta) = M_A_z - 0.8*9.81*0.075*sin(theta) ==> M_A_z = 6 * 10^-3 * 2 sin(2theta) + 0.8*9.81*0.075*sin(theta)

Last edited by a moderator:
Delta2
Tymofei said:
Thats my question.As you see coordinate system was located at center of mass.I just shifted it to point A and recalculated values.
I could be wrong, but I think that the center of mass of the rod is located at point ##A##. The rod passes through the slot in the table so that you see only half of the rod in the figure. Hope I'm not misinterpreting the problem statement.

Delta2
TSny said:
I could be wrong, but I think that the center of mass of the rod is located at point ##A##. The rod passes through the slot in the table so that you see only half of the rod in the figure. Hope I'm not misinterpreting the problem statement.
I don't thinks so,because in original solution it was placed at the center of rod,and inertia was calculated as '1/12*m*l^2' which gives you inertia about center of mass.

But isn't point ##A## at the center of the rod?

Tymofei, Delta2, PhDeezNutz and 1 other person
TSny said:
But isn't point ##A## at the center of the rod?
View attachment 262907

I didn't think so,but i guess you are right.
Thats the only way which explains .. thanks

PhDeezNutz

## 1. How do you calculate the moment from a different vantage point?

The moment from a different vantage point can be calculated by using the formula M = F x d, where M is the moment, F is the force applied, and d is the distance from the pivot point.

## 2. What is a moment in physics?

In physics, a moment is the product of a force and the distance from the pivot point at which the force is applied. It is a measure of the tendency of a force to cause an object to rotate around an axis.

## 3. Why is it important to calculate the moment from a different vantage point?

Calculating the moment from a different vantage point allows us to understand the rotational effects of a force on an object. This is important in many fields, such as engineering and physics, as it helps us analyze the stability and balance of structures and systems.

## 4. Can the moment be negative?

Yes, the moment can be negative. This occurs when the force and the distance are in opposite directions, causing the object to rotate in the opposite direction. A negative moment is also known as a clockwise moment.

## 5. How does changing the vantage point affect the moment?

Changing the vantage point can affect the moment by changing the distance from the pivot point at which the force is applied. This, in turn, can change the magnitude and direction of the moment, as well as the stability and balance of the object. It is important to consider different vantage points when analyzing the moment in order to fully understand its effects.

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