Final answer:
The primary principle demonstrated in a completely elastic conservation of linear momentum experiment is the conservation of linear momentum.
Step-by-step explanation:
The primary principle demonstrated in a completely elastic conservation of linear momentum experiment is the conservation of linear momentum.
In a completely elastic collision, the total momentum of the system is conserved. This means that the sum of the momenta of the objects before the collision is equal to the sum of the momenta after the collision.
For example, if two balls collide elastically, the total momentum before the collision is equal to the total momentum after the collision.