# Principle of superposition

step 1
i have a spring with two ends i and j. I fix i and pull j to a displacement and measure the force at i and j called fi and fj

step 2
now i fix j and pull i to a displacement and measure the force at i and j called fi and fj

principle of superposition says that the total force at i and j (Fi and Fj)is equal to

Fi=fi(step1)+fi(step2)
Fj=fj(step2)+fj(step2)

i don't understand how the forces in both the steps are added. What is the principle of superposition

is there any website ?