Final answer:
A concussion is the type of injury caused by an external force contacting the head and causing sudden motion.
Step-by-step explanation:
An injury that is caused by an external force contacting the head, placing the head in sudden motion, is known as a concussion. A concussion is the mildest and most common type of brain injury, often resulting from contact sports or accidents. When an individual experiences a sudden impact or blow to the head, their brain may move rapidly inside the skull, leading to this type of injury. Symptoms can include headache, drowsiness, and confusion, but usually, a concussion heals on its own within a few days.