Yes- they can physically move things and harm people.
They can throw thigs around, play havoc with electricity abd harm people
a person who studies paranormal thing or unusual things including ghosts, poltergiests, and ufo's
that depends on the frequency of the rays of light.
It depends what kind of ghost. Demons are evil, they do nasty things to people, like in paronormal activity. Spirits are usually ancestors who are simply watching over you. They do not wish to harm you. Poltergiests do not hurt you, but they damage your belongings. There are many other types that do not fall into these catergories, but they are not as common as the above. These are the most common varieties. :)
They eat you...
If demon means something evil, they can harm us.
intend to do us harm
they get into our blood stream
they have claws to pinch us and the stinger at the back can sting us :)
they become harmful to us at night when they exhale carbondioxide
Contamination of water sources with pollutants or toxic chemicals can harm human health. Flooding and tsunamis can cause destruction of property and loss of life. Climate change impacting the water cycle can lead to more frequent and severe droughts or floods, affecting access to clean water and food security.
The UV radiation can harm us by causing eye cataract. You can protect yourself by planting more tress to avoid UV's.