Simulator Background Properties: To open the simulator background Properties Box, depress Select. Then double-click or control-click in a clear area of the simulation window. In the Properties Box, you can set a wide variety of properties. These properties are discussed in detail under the topic headings listed below.

• X enabled / Y enabled: These options control whether or not the X-axis and Y-axis are displayed. Both axes are automatically hidden when vertical springs or tracks are placed.
• X grid enabled / Y grid enabled: These options control whether or not horizontal (X) and vertical (Y) grid lines are displayed. All grid lines are automatically hidden when vertical springs or tracks are placed.
• Horizontal / Vertical step: These properties set the size of the intervals on the X-axis and Y-axis. The step sizes are in terms of distance measures, such as meters (the default), rather than pixels. An axis interval is equal to two grid intervals.

The step sizes are also controlled by three hotspots located near the grid's origin. The scales controlled by the hotspots are indicated in the figure to the right. To change the X and Y scales, click-and-drag the hotspots. Changing step sizes using hotspots does not change the values in the background properties. The origin itself is a hotspot that you can click-and-drag to a new location.

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• Show other forces on Run: During Run mode (simulations) and Pause mode, either display or hide force vectors other than those listed in the next bullet.
• Show gravitational / normal / friction / elastic forces on Run: During Run mode (simulations) and Pause mode, either display or hide the indicated force vectors.
• Show velocity on Run: During Run mode (simulations) and Pause mode, either display or hide velocity vectors.
• Show acceleration on Run: During Run mode (simulations) and Pause mode, either display or hide acceleration vectors. This is the only show on Run option not enabled by default.
• Show total net force before Run: During Stop mode, either display or hide the total force vector (the thick black arrow).
• Show forces before Run: During Stop mode, either display or hide force vectors.

• Show path: This option enables the rendering of the path traveled by a body during Run mode (simulations). The simulator renders the path by drawing a representation (see next bullet) of the path at regular intervals. The path remains on display in Stop mode after the simulation concludes.
• Represent Path as: This option determines how the simulator represents the path. The choices are:
  • dots of the same color as the body;
  • pictures of the body;
  • velocity vectors that represent the body's velocities at the times the representations are drawn; and
  • acceleration vectors that represent the body's accelerations at the times the representations are drawn.
• Display path, steps: This property determines how frequently the simulator draws a representation of the path. This property sets the number of "refresh steps" between renderings. Hence, the time interval between subsequent renderings of the path is the product of this property and the refresh time.

• X motion / Y motion enabled: These options determine whether or not bodies can move horizontally (X) or vertically (Y). Default is for motions in both directions to be enabled. Even if motion is confined to one direction, vectors are not. A body limited to movement along the X-axis could still have a velocity vector pointing 45º off axis.

• Gravitation source: Choose one of three gravitation sources (Earth, Moon, or Jupiter) or choose to have no gravity (default). A graphic in the lower right corner of the simulation window depicts the current choice (a picture of Earth, the Moon, or Jupiter, or a picture of "space" [a star field] for no gravity). Gravity is a constant acceleration in the -Y direction. Enabling gravity disables the acceleration tool.
  
  When gravity is present, all bodies have gravity force vectors attached that are labeled "Gravitational force." Bodies on tracks also experience normal and possibly friction forces.
  
  To enable the next two properties, you must enable gravity first (click Apply).
• Show zero level of gravitational potential energy: Show the zero level as a thick dashed green horizontal line.
• Zero level of gravitational potential energy: The Y coordinate (in meters or another distance measure) of the zero level line. Default value is zero.

• Stop time, seconds: The duration of simulation runs (i.e., Run mode), provided that the Stop button is not pressed. The default duration is 10 seconds. The maximum duration is 30 seconds.
• Refresh time, ms: This property determines how often the simulator refreshes the simulation window during simulation runs (Run mode). The default refresh time is 100 ms or 0.1 sec. The minimum is 20 ms and the maximum is 200 ms. Low refresh times are more computationally intensive than high refresh times but may provide more accurate results, especially with regard to complicated motions.
  
  Together with the Display path, steps property, the refresh time also determines how often the simulator renders a body's path.