Gravitation; law; gravity, center of; weight. Equilibrium 3 forms; stability, how increased. Falling Bodies; velocity, acceleration, "g," Laws; _V_ = _gt_, _S_ = (1/2)_gt_² - _s_ = (1/2)_g_(2_t_ - 1). Pendulum; simple, seconds, laws (3), _t_ = π√(_l_/_g_). CHAPTER VI WORK AND ENERGY _104. Work._--"Whenever a force moves a body upon which it acts, it is said to do work upon that body." For example, if a man pushes a wheelbarrow along a path, he is doing work on it as long as the wheelbarrow moves, but if the wheelbarrow strikes a stone and the man continues to push and no motion results, from a scientific point of view he is then doing no work on it. "Work signifies the overcoming of resistance," and unless the resistance is overcome no work is done. Lifting a weight is doing work on it, supporting a weight is not, although the latter may be nearly as tiresome as the former. Work as used in science is a technical term. Do not attach to it meanings which it has in every-day speech. =105. Measurement of Work.=--Work is measured by the product of the force by the displacement caused in the direction of the force, that is _W_ = _fs_. Therefore if a unit of force acts through a unit of space, a unit of work will be done. There are naturally several units of work depending upon the units of force and space employed. _English Work Unit._--If the force of one _pound_ acts through the distance of one _foot_, a _foot-pound_ of work is done. A foot-pound is defined as the work done when 1 lb. is lifted 1 ft. against the force of gravity. _Metric Work Unit._--If the force is one _kilogram_ and the distance one _meter_, _one kilogram-meter_ of work is done. _Absolute Work Unit._--If the force of one _dyne_ acts through the distance of one _centimeter_ a _dyne-centimeter_ of work is done. This usually is called an i. Other work units are sometimes used depending upon the force and distance units employed. One, the i, is equal to 10,000,000 ergs or 10⁷ ergs. =Problem.=--If a load is drawn 2 miles by a team exerting 500 lbs. force, how much work is done? =Solution.=--Since the force employed is 500 lbs., and the distance is 2 × 5280 ft., the work done is 500 × 2 × 5280 or 5,280,000 ft.-lbs.