1. What is the net force on a bathroom scale when a 150-pound person stands on it?
2. Suppose you stand on two bathroom scales with your weight evenly distributed between the two scales. What is the reading on each of the scales? What happens when you stand with more of your weight on one foot than the other?
1. Zero, for the scale remains at rest. The scale reads support force (which has the same magnitude as weight), not the net force.
2. The reading on each scale is half your weight, because the sum of the scale readings must balance your weight, so the net force on you will be zero. If you lean more on one scale than on the other, more than half your weight will be read on that scale but less on the other, so they will still add up to equal your weight. Like the example of Nellie hanging by the rings, if one scale reads two-thirds your weight, the other scale will read one-third your weight.