Using sketches of a box sitting on the table, the forces if gravity, tension, and forces pulling toward the right and left are shown as vectors. The length of the vectors indicate the relative size of the forces. Vector quantities are defined as having magnitude and direction, examples are weight and velocity. Mass, time, liquid measurement, and area are defined as scalar quantities, containing magnitude but no direction. A kilogram mass was hung from a spring balance and the force shown as about 10 Newtons. The forces were labeled positive and negative and the net force shown as zero. The equilibrium rule was derived as "the sum of the forces equal zero in a state of no physical change. Two spring balances suspended a small shelf of wood and 2x250 gram masses were placed, one at each end. The sum of the downward forces equaled the sum of the upward forces. As one mass was moved closer to the other, the force increased on one side and decreased on the other, however, the net sum was always the same. A thought problem regarding how much would each of two scales show if you stood with one foot on each.