'Used to show the effect of mass - radius and velocity on the centripetal force of a rotating body. This simple but effective system makes a complicated topic into one of the most enjoyable lessons possible. A spring system is enclosed in an acrylic tube so that the student can whirl a rubber ball around in a horizontal circle to measure the centripetal force. Radius and mass are easily varied and rotational speed is simply measured by timing the revolutions. The forces acting can be measured in "force increments" or in Newton''s if the spring is calibrated beforehand. Full instructions included. Econo version: This experiment uses the weight of one to 20 1g masses from one end of a cord as a counterweight to the pull of a rubber weight swinging in a circle overhead. Includes handle - sturdy cord - rubber weight - masses (20) and instructions.'