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Old Feb 24th 2011, 08:47 AM   #1
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Calculating the effect of a single force vector on multiple points

To preface this, I have never taken physics, and I am a Computer Science student faced with a problem.

My problem is as follows:
Create a grid of triangles to represent fabric. Each point on the grid is connected by a "spring" to six other points.

To start the effect of a swinging force on the fabric, apply the force to a single point on the grid. Then go through the grid and spread the effect of the force on the adjacent points. Do this for every point on the grid.

What I need help with is finding the effect of a single vector (at the point) on the six surrounding points:


What I'm doing so far:
1. Find the "vector" connecting each of the six points to the center (A) point.
2. Calculate the angle between the found vectors and the force vector at A
3. The force exerted on each of the six points has some relation to the angle between the two vectors???
- I tried projecting one vector onto the other, but that creates bizarre results.
Note that I need the force vector for all the points Q... U

Force of Gravity will be added in after the forces at all the points are calculated.

After I calculate the forces at all the points, I will then use Hooke's law to calculate the displacement from the original point on the grid.

Information I have available for calculation:
-size of grid
-mass of points
-force gravity
-swing force vector
-original coordinates of points (with which I can calculate angles and vectors between stuff)

Here's another picture describing the situation (in this case for a single triangle, e.g. a corner case)


Also note, I have implemented Quaternions and their basic operations so if that helps they can be part of the solution.

Last edited by birdz; Feb 24th 2011 at 09:06 AM.
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Old Feb 24th 2011, 08:57 AM   #2
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Originally Posted by birdz View Post
To preface this, I have never taken physics, and I am a Computer Science student faced with a problem.

My problem is as follows:
Create a grid of triangles to represent fabric. Each point on the grid is connected by a "spring" to six other points.

To start the effect of a swinging force on the fabric, apply the force to a single point on the grid. Then go through the grid and spread the effect of the force on the adjacent points. Do this for every point on the grid.

What I need help with is finding the effect of a single vector (at the point) on the six surrounding points:


What I'm doing so far:
1. Find the "vector" connecting each of the six points to the center (A) point.
2. Calculate the angle between the found vectors and the force vector at A
3. The force exerted on each of the six points has some relation to the angle between the two vectors???
- I tried projecting one vector onto the other, but that creates bizarre results.

Force of Gravity will be added in after the forces at all the points are calculated.

After I calculate the forces at all the points, I will then use Hooke's law to calculate the displacement from the original point on the grid.

Information I have available for calculation:
-size of grid
-mass of points
-force gravity
-swing force vector
-original coordinates of points (with which I can calculate angles and vectors between stuff)

Here's another picture describing the situation (in this case for a single triangle, e.g. a corner case)


Also note, I have implemented Quaternions and their basic operations so if that helps they can be part of the solution.
The net force caused by the springs as a reaction to the force applied at the center will be a force directed opposite the applied force and have the same magnitude. You can find out how much force is on an individual spring by taking components.

Since there is no rotation going on I can't see how quaternions are going to be of any help here.

-Dan
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Old Feb 24th 2011, 12:25 PM   #3
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Originally Posted by topsquark View Post

Since there is no rotation going on I can't see how quaternions are going to be of any help here.

-Dan
Technically the force being applied is a rotational force, because the whole mesh object is rotating, but I already have that down OK.

Originally Posted by topsquark View Post
The net force caused by the springs as a reaction to the force applied at the center will be a force directed opposite the applied force and have the same magnitude. You can find out how much force is on an individual spring by taking components.
Yes, I understand that the spring force will be equal and opposite magnitude to the force. What I don't understand is how to calculate the components.

But than you very much for the very fast reply!
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