In-group/out-group bias is the tendency to include members of other groups into one's own group.
see all members of an out-group as the same.
show negative feelings toward members in other groups.
show sympathy toward members of other groups.

You are traveling in a car going at a constant speed of 100km/h down a long, straight highway. you pass another car going in the same direction which is traveling at a constant speed of 80km/h. as measured from your car's reference frame this other car is traveling at −20km/h. what is the acceleration of your car as measured from the other car's reference frame? what is the acceleration of the other car as measured from your car's reference frame?