falling versus falling down
Der Himmel fällt. This site ONLY translates this as the sky is falling down. My answer "The sky is falling" is incorrect, according to the admins. Die Blumen fällt: the flowers are falling (or fall), Die Bäume fällt: the trees are falling (or fall), and Der Apfel fällt: the apple is falling (or falls) are all the correct answers, but only when referring to the sky falling is down used. I tested a theory just now and got "the trees are falling down" wrong for Die Bäume fällt. So the sky is falling down, but the trees are not falling down. The issue I have is the sky can only falling in one direction, down. When something falls, it falls downward; so the direction is implied and does not have to be noted. HOWEVER COMMA if you admins persist in the correct answer for Der Himmel fällt to be "the sky is falling down", then down should be uniform for anything falling.
Rant complete. Continue about your day!
I'm trying to figure out whether or not English has a pattern for falling and falling down. I think falling down is generally, but not exclusively, used for people having accidents, as in "she fell down the stairs." In this case "down" is required because "she fell the stairs" would not make sense. But you can also fall through things, as in "he fell through the ice." In these cases, the direction is necessary to complete the statement. Otherwise it seems optional. "She fell" and "she fell down" are both acceptable as complete statements.
It's possibly that "the sky is falling" doesn't use down because it's only a metaphoric fall and nothing actually hits the ground. This explanation is purely speculative.
These are strange examples. Anyhow, I'll try to give some sort of explanation.
1) "Der Himmel fällt."
While grammatically correct, I'm pretty sure nobody would ever say that in German. The only application that I am aware of is in a (dated) idiom: "Der Himmel fällt mir auf den Kopf." (Expressing being overwhelmed by events or circumstances.)
2) Indication of direction
In most cases, adding a direction to the verb is required when the direction is NOT down. However, leaving the direction away often is close to the english continuous form. Examples:
Der Baum fällt um. (The tree falls over / toppled)
Sie fällt hin. (She falls down, but indicating the end result of lying on the ground)
Sie fällt. Now this is a contextual thing. If context provides that she was standing or walking, etc., on the ground, it really implies the end result. However, suppose she falls from a cliff, this would be close to the english continuous form: She is falling.
Das Glas fällt runter. The glass falls down, again indicating the end result of it ending up on the ground or floor.
Er ist die Karriereleiter hinaufgefallen. Metaphorical use, indicating someone rose in a company's hierarchy not due to his work, but other circumstances like influential friends / family.
3) Beware of another german verb that is very close to "fallen": "fällen".
The difference is that "fällen" is something active. Einen Baum fällen: To fell a tree. Actually, I can't think of another use for physical things, but "fällen" is also used metaphorical: "Eine Entscheidung fällen" To make a decision. "Sein Faustschlag fällte seinen Gegner." His punch dropped (fell?) his adversary.
Hope that helps a bit.