"Ducks can float well on water."
Translation:오리는 물에 잘 떠요.
. Can't think of any good reason for "can" to be omitted in the translation apart from perhaps, it is to point out that there isn't a need to do so if the ability is an innate characteristic of the subject. (Same as in English, "Ducks float. Fish swim"...) ?
. What is the difference between 뜨다 and 떠다니다?
뜨다 has various meanings.
(1) When used as "to float", it describes either a sensation or the state of staying on the surface of a liquid (not going under). For this semi-stative meaning, the postposition 에 is applied to indicate position and location. Hence,
에 뜨다 = stay afloat in; float on.
흰 구름이 하늘에 떠 있다 = White clouds are staying afloat in the sky
(2) To describe the active/dynamic "to float", a motion verb is usually added (cf. Compound verb). The analogy here to English is the addition of preposition s.a. (float) in, (float) across, (float) away ...
공간에서 떠다가다 = float in space [떠 <-- 뜨다]
(3) with 에서 뜨다, 뜨다 is used as a dynamic verb. It stands for "to rise".
에서 뜨다 = rise from
해는 동쪽에서 뜨고 서쪽으로 진다 = The sun rises in (/from) the east and sets in the west.
~에 doesnt specifically imply that something is INSIDE something. It just means that one object is roughly in some place. 바나나는 냉장고에 있어 - a banana is in (inside) the refrigerator. 사진은 벽에 있어 - a picture is on (on the vertical surface of) the wall. 사람은 해수욕장에 있어 - a person is on (on the horizontal surface of) the beach