What are two situational examples of unbalanced forces?

An example of a balanced force is two cards leaning against each other and not falling over, or two football players blocking each other but neither overpowering the other. An example of an unbalanced force is two cards leaning on each other then falling over, or two football players blocking each other, then one tackles the other.

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray