Meaning trap
act up
not work properly
to stop working correctly or cause problems, especially for machines, devices, or body parts.
Don't mix these meanings
Same phrase, different job.
to stop working correctly or cause problems, especially for machines, devices, or body parts.
Another meaning of 'act up' is 'misbehave'; compare the examples to keep the meanings separate.
Hear it in context
Notice where the phrase sounds natural.
My laptop started acting up right before my online meeting.
Sometimes, my internet connection acts up during important video calls, which can be very frustrating.
Fix the pattern
One small grammar move makes it sound right.
Not: My back has been acting out lately.
Say: My back has been acting up lately.
It's 'act UP' (playing up); 'act out' means express feelings through bad behaviour — a different thing.
Which sounds natural?
Tap the one a native speaker would say.
'Act up' is the casual way to say a device or body part is playing up; 'malfunctioning intermittently' is technical.
Build natural chunks
Words that usually travel with it.
act up (device/body part)
- my knee
- the engine
- the wifi
- again
Don't confuse it
Related
Other meanings and phrases to compare.
- act up (misbehave) — Another meaning of 'act up' is 'misbehave'; compare the examples to keep the meanings separate.