It is harder to sit ups with your legs flat than having your knees bent, because your center of gravity will be farther away making it more difficult.
The long pole has more mass that can be distributed, which help the walker will stay balanced and lower their center of gravity.
In relation to Newton's first law due to a force of habit the occupant moves in a path of a straight line. In Newton's third law the floor intercepts her path and moves against their feet, because the floor is pushing on her feet while her feet is pushing against the floor. The centripetal force is what keeps her moving in a circle, which is caused by the floor pushing