| Track: This tool allows you to simulate motions of objects that are confined to run on a track. Place between one and three tracks anywhere in the simulation window. You must click toward the middle of the window. Placing a track turns off the grid. A track has three black sections. The sections are connected by two blue center joints. In addition, the left and right sections both terminate in blue end joints. To move the track, click-and-drag the sections. To resize the center section, click-and-drag a center joint to the left or right. To resize and/or change the angle of the left (right) section, click-and-drag the left (right) end joint until the section has reached the length and is oriented in the direction you desire. You can also change the angles of the left section (Section I) and the right section (Section II) in the track's Properties Box. The maximum angle for either section is 60º with respect to the horizontal axis. To place body elements on the track, you must click within about 30 pixels above or below the track. When on the track, the body has a square, rather than round, shape. You cannot resize the body, nor can you represent the body with an image from the clipboard. You can move the body along the track. But you cannot remove the body from the track. Body elements on tracks experience normal forces when gravity is present. You can also place launchers, exploders, and horizontal springs on tracks. In the track's Properties Box, when gravity is present, you can set the roughness of each section of the track. The roughness determines the magnitudes of friction forces. A body of 1 kg in Earth gravity (9.8 m/s2) on a horizontal track with a roughness of 1.0 experiences a friction force of 9.8 N. You can also choose to show (or not show) the zero level of gravitational potential energy (the dashed green line). Default is to show. For tracks, the zero level is always the vertical position of the horizontal track. Caution about Run mode: During Run mode, if a body moves off a track, the simulation will stop.