Is it ok if I use gps traces data uploaded by other users to do some research about the mobility of human being?(not for profit or business!!!)
I don’t know whether this kind of behavior will violate some rules of OSM, like user privacy and so on.
First of all it is good to ask about using it 
when googling about “openstreetmap GPX traces liocence” I found the following topic that are helpful perhabs:
According to http://www.osmfoundation.org/wiki/License/We_Are_Changing_The_License the GPS data is now also under ODbL
If a user has uploaded his GPX traces, he agreed that this data can be published under the licence that is valid.
But you can do own internet serach about that topic
If you do not break ODbL you can do any research with that data you want.
Do you also know http://wiki.openstreetmap.org/wiki/Research ?