Actual asnwer is: US (us also means we)
iT CAN BE WRITTEN AS " vi "..WEN HEARD ....IT WILL BE we.............
Either you spell "we" or only "V" it turns out to be same when heard.
Us is a synonym for we.
"VI" spells like we
"US" is a synonym of we
The two of us keep a low profile
Without us you would not be mobile
Seldom looked at but frequently used
We're often depressed but not abused
Side by side with functions opposite
Managing the go and stop of it
What are we?