What is a phrasal verb?
It's the combination of a verb + a particle (preposition or adverb) resulting in a new word.
BE CAREFUL: The new meaning of the word combination is different from the two separate words.
Phrasal verbs are very common in spoken and written English so we need them to understand and speak natural English.
Act up.- (child, car, computer, injury)
When somebody or something acts up, they behave badly, hurt or don't work properly.
This computer's acting up again.
The children were acting up because their mother wasn't there.