The challenge in defining child abuse stems from the difficulty in determining what actually constitutes the degree of severity required to consider an incident as being abuse.
"Child abuse may involve physical abuse that causes injury." The challenging word is the word "may." Physical contact with a child such as beating, burning, or shaking a child may be considered as being abuse, but the severity of the contact enters into the determination of whether or not a charge of child abuse is warranted.
Sexual abuse of a child may or may not cause any physical injury, but can still be considered child abuse. Sexual abuse covers inappropriate contact with a child as well as having intercourse. Similarly, child neglect may not result in physical injury, but leaving a child unattended or placing a child in a position that is potentially risky can be considered child abuse.