Objectivism/A car cannot run on the fuel of belief

After TAing in US for 2 years i am getting acquainted with fairly sizable number of young undergrads. Teaching Physics is fun...both scientifically and philosophically.

Some might argue that the two things are uncorrelated. i.e. A person may have different philosophical approach and different scientific approach. A priest can be a scientist...ha ha :D Why not? Many teachers preach their beliefs, teachings etc. But wait a minute, I can talk about this later....right now let me tell you something interesting..

Some of my students answer the physics question with a "belief" that the answer could be wrong because they "believe" that they are not good enough at experiments. Or sometimes they say that they "believe" that the results should be so but are getting otherwise. For well proved theories let us say the second answer is fairly acceptable. But not all the theories are full proof. Questioning with a fair amount of objectivism is necessary...which is what a scientist would do. But how does one teach/preach such an attitude?