
aufpassen
to pay attention
To direct one's attention to something or someone so as not to miss anything or in order to learn something; to be focused.
Pass gut auf, ich erkläre es nur einmal.
Pay close attention; I will explain it only once.
to pay attention / watch out
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to pay attention
To direct one's attention to something or someone so as not to miss anything or in order to learn something; to be focused.
Pass gut auf, ich erkläre es nur einmal.
Pay close attention; I will explain it only once.

to look after
To take care of someone or something and make sure there is no danger or that nothing bad happens; to supervise someone.
Kannst du heute Abend auf die Kinder aufpassen?
Can you look after the children this evening?

to watch out
To be careful and attentive in order to avoid an accident or a mistake.
Pass auf, der Boden ist frisch gewischt und sehr rutschig!
Watch out, the floor has just been mopped and is very slippery!
'Aufpassen' is a separable verb. In a main clause, the prefix 'auf' goes at the end. In subordinate clauses and in the infinitive with 'zu' (to), the verb stays together.
Ich passe im Unterricht immer gut auf.
I always pay close attention in class.
The imperative 'Pass auf!' can mean two things: 'Pay attention!' or 'Watch out!'. The situation and tone of voice make clear which meaning is intended.
Pass auf, diese Aufgabe ist schwierig.
Pay attention; this exercise is difficult.
When 'aufpassen' means to take care of someone or something, it is always used with the preposition 'auf' and the accusative.
Meine Nachbarin passt oft auf meine Katze auf.
My neighbor often looks after my cat.
To say what someone should watch out for, a subordinate clause with 'dass' (that) is often used. This specifies the danger or possible mistake.
Pass auf, dass du nicht auf dem nassen Boden ausrutschst.
Watch out that you don't slip on the wet floor.
to pay attention / to respect
Achten auf and aufpassen can both mean being attentive and careful. “Achten auf” directs attention specifically to a particular person or thing, while “aufpassen” places more emphasis on current concentration or caution in a situation. “Achten auf” often fits a specific warning, while “aufpassen” fits concentrated listening or general caution.

Bitte passen Sie im starken Verkehr besonders gut auf.
Please be especially careful in the heavy traffic.
Bitte achten Sie auf den Verkehr, wenn Sie die Straße überqueren.
Please watch out for traffic when crossing the street.