Run: Clicking on the Run button starts or resumes Run mode. Run mode is the simulation mode and the only mode in which physics works. Bodies move in response to speeds and forces. Bodies are subject to gravitational, normal, and friction forces. Launchers function. Users can activate thrusting forces using the space bar. Run mode lasts until the Stop time (as recorded by the clock) set in the background properties (default =10 sec), or until stopped.

Depressing the Pause button only suspends the simulation; it does not halt it. Clicking on the Run button while in Pause mode resumes the simulation; it does not restart it.

Starting a simulation from Stop mode always resets the clock, which only functions during Run mode. Resuming a simulation from Pause mode restarts the clock from the paused time.

In Run mode, you cannot access the Standard Menu. In addition, nearly all elements and tools are not accessible. The only usable buttons are Stop and Pause. In addition, you cannot access objects to move them or change their properties

Exception: If you select objects before entering Run mode, you can open their Properties Boxes during Run mode by typing control-O.

In the case of graph tools and energy bar tools, this feature has some use, because you can actually change the displays of these tools during a simulation run.

Changing a selected body's mass (in the Properties Box) might roughly simulate an inelastic collision or the separation of a rocket stage.

Other than that, changing the properties of or trying to move selected objects during Run mode either has no effect or the effect is inconsequential.