The most common physical effects are probably those connected to the weather, such as wind, snow, rain and fog.
A common observation on film shoots by members of the general public is, “Why are you creating rain when it’s already raining?” But the truth is that a filming schedule can’t be left at the mercy of the British weather, and that by using effects a degree of control and repeatability can be achieved. This approach can be applied to something as simple as a fire burning in a grate. Filming a scene takes time, and to avoid the continuity issues of having a fire burning down, and then having to be replenished with new fuel, almost all fires seen in television productions are created using ceramic or plaster logs and a controllable gas flame.
Reuben (Colin Douglas) and the Doctor (Tom Baker) peer through the fog in Part One of Horror of Fang Rock (1977).