Final answer:
The safety net test referred to is a 'drop test'. This concept is linked to impulse, where extending the time over which an object comes to rest reduces the impact force. Free-body diagrams are used to visualize the interactions of these forces.
Step-by-step explanation:
The test that measures the ability of safety nets to absorb the force of a 400-pound bag of sand dropping into the net is referred to as a "drop test". This type of test ensures that the net can handle the anticipated loads and prevent injuries or damage.
It relates to the concepts of impulse and the force of impact, where the time over which a force acts on an object is crucial to reducing the effect of an impact, as explained by the principle of impulse in the provided reference material. Free-body diagrams help to visualize the forces at play, including the force of gravity and the normal force or restoring force that acts to counterbalance it.
Ultimately, the net must be tested to ensure it can safely bring to rest objects that may fall into it without breaking or allowing the object to hit the ground, much like the net force on car occupants is managed by airbags and padded dashboards during collisions to increase the time over which a stop occurs and therefore decrease the force on the occupants.