Final answer:
A goalkeeper in soccer is not allowed to body check an opponent as it is against the rules. Protective equipment like shin guards and protective cups are essential for preventing common soccer-related injuries. A reference frame in physics refers to the perspective from which motion is observed; two people side-by-side would share the same reference frame.
Step-by-step explanation:
In soccer, a goalkeeper is not allowed to body check an opponent. The rules of soccer specifically prohibit this type of physical contact, and doing so could result in a foul or even a yellow or red card, depending on the severity and intent of the check. The goalkeeper's role is to safeguard the goal and handle the ball within the confines of the penalty area, using their hands and body to stop shots legally. Any aggressive action like a body check against opponents is against the rules.
Protective equipment in soccer typically includes shin guards and, in some instances, a protective cup, especially for male players. These items are designed to protect players from common soccer-related injuries, such as a ball-kick or physical collision, particularly in sensitive areas like the shins and groin.
The concept of a reference frame is more of a physics topic. If two people are standing side-by-side watching a soccer game, they would be in the same reference frame, meaning they observe the motion of the players and ball against the same background or set of surroundings.