using LinearAlgebra

# stress tensor
S = [100 100 160; 100 0 -150; 160 -150 -60]

# unit normal vector
q = [1/2.0, 1/2.0, 1/sqrt(2.0)]

# tension vector and its norm
p = S*q
pn = norm(p)
println("tension    = ", pn, " Pa")

# the angle (in degrees) between the direction of the tension and the normal
alpha = acosd(p'*q/pn)
println("alpha      = ", alpha, " deg.")

# tangential component of the tension vector
ptang = pn*sind(alpha)
println("tangential = ", ptang, " Pa")

# tangential component of the tension vector
pnorm = pn*cosd(alpha)
println("normal     = ", pnorm, " Pa")