Static field on plastic slide only during day not night Can anyone fully explain why- A modern kids park play ground slide made of plastic has a static field of electrons gathered on it only during the day and never at night?
 A: Here's a possibility that might not normally be considered, but since other factors seem to be controlled for, it might be relevant:
Plastics are well known to slowly photodegrade in direct sunlight, because the UV radiation tends to break some of the weaker bonds in the plastic. This suggests that the UV radiation that reaches the ground might be energetic enough to serve as ionizing radiation for some of the weaker-held electrons in the plastic. Therefore, it might be the case that the surface of the plastic is being ionized by the UV radiation from the Sun. Humidity would affect the rate of accumulation of this charge, but doesn't actually explain where the charge comes from, if nobody is touching the slide.
A: Maybe for the humidity of air at the night. The wet air can "absorb" more electric charge than dry air.
A: As Probably_someone said, charge must come from the slide itself if nobody is sliding on it. The heat from the sun gives the electrons in the slide more energy, and they will be more likely to escape the bond they have with their respective atoms. The built up charge will be lost to the environment as well, and there will be some equilibrium point where the rate of dissipation equals the rate of electron emission. During the night there is less heat, so less charge is created. The charge built during the day will dissipate into the air and there will be no noticeable static charge.
I would add also that plastic is an insulator, so charge cannot flow from the surface of the slide to the ground, unlike metal slides, which do not suffer from this problem.
