Other Lessons
Forces allow you to override the physical state of a PLC input or output.
I'm going to give you a few personal views on when and how to use forces but first let's understand how to know if forces exist in a PLC, how to force an input or an output, and how exactly forces are used in the PLC.
Tim's opinion of forces
I try to be really objective in providing this content and include a lot of "rules" that are not based in facts of how the PLC operates, however forces are something I see misused and unsafely used by new PLC programmers. As I state at the end of this video about forcing, I probably haven't used a force in years outside of making lessons about forces. And I think the big thing I see newcomers do is force bits because they can't figure out why the PLC program isn't doing what it is supposed to. The root cause of this is usually not fully understanding how a PLC scans and executes programs. So really concentrate on grasping these core concepts.
The other very important comment I would have about the use of forces is try not to leave forces installed on a machine. If I walk up to a PLC and I see a force light on, it is a red flag that there could be an unsafe condition.
Practice understanding the difference between input and output forces. Also the video below will be very helpful in understanding how each affects the PLC program.