Final answer:
A device used for impact testing is a pendulum, consisting of a 21 kg mass, its mass center, and radius of gyration. The distance for the pendulum is selected based on the desired testing conditions.
Step-by-step explanation:
The device used for impact testing is called a pendulum. It consists of a 21 kg mass that is attached to a string and swings back and forth. The key components of the pendulum are its mass center and radius of gyration.
The distance for the pendulum is usually selected based on the desired testing conditions. The length of the string determines the period of the pendulum's swing. A longer string will result in a slower period, while a shorter string will result in a faster period.
By adjusting the length of the pendulum, scientists can control the impact force and study the effects of different conditions on materials or structures.