Can someone explain the concept of relative velocity in physics?

[Bashyboy]

At the present moment, I am reading a section in my physics textbook concerning relative velocity. In an example the author provides, he states that two trains are traveling in opposite directions at a speed of 80 km/h; and relative two each other they are traveling at a speed of 160 km/h. Somehow, I cannot see why this is true, perhaps I have an underdeveloped physical intuition. Could someone help me with this concept?

Thank you

 

[jtbell]

Imagine yourself driving one train. As you look out the front window, you watch the other train approach. Doesn't it come towards you twice as fast as an object sitting on the ground next to the track would?

(Substitute "car" for "train" if that brings the situation more within the realm of your experience.)

 

[Bashyboy]

Yes, it makes perfect sense, now. I feel like a bloody idiot.