Sums of Forces and Moments

Extraction of sums of forces and moments from MecLib images.

Question Variables

Unit vector from a force object

unitvec(l):=block( [v] , v:round((l[4]-l[3])*10),v/sqrt(v[1]^2+v[2]^2));

Sign of a moment object

msign(l):=block( [v1,v2] , v1:l[4]-l[3],v2:l[5]-l[3],round(signum(v1[1]*v2[2]-v1[2]*v2[1])));

Moment of a force object about a reference point

moment(l,p):=block( [f,r] , f:unitvec(l),r:l[3]-p, r[1]*f[2]-r[2]*f[1]);

Feedback Variables

• rp reference point
• lu symbolic length unit
• objects Input field with object list
• names Input field with object names

rp:[0,0];
lu:a;
data: stackjson_parse(objects);
f:[0,0];
for i:1 thru length(data)  do ( if (data[i][1]="force") then f: f+names[i]*unitvec(data[i])); 
m:0;
for i:1 thru length(data)  do ( if (data[i][1]="force") then m: m+names[i]*lu*moment(data[i],rp)); 
for i:1 thru length(data)  do ( if (data[i][1]="moment") then m: m+names[i]*msign(data[i])); 

PRT Node

Display of the sum of forces and moments (use standard feedback format).

<p>\( \displaystyle \Sigma F_x={@f[1]@}\) </p>
<p>\( \displaystyle \Sigma F_y={@f[2]@}\) </p>
<p>\( \displaystyle \Sigma M_0={@m@}\) </p>