- #1
reiternick
- 2
- 0
I don't know if you guys have heard that, when a railroad car is about to start moving, railroad operators sometimes have the train go backwards a little bit at first, that way when they move forward the force of the engine car only has to overcome the Static friction of one cart at a time, as opposed to starting from rest and having to overcome the static friction of all carts at the same time (which would be harder than using the trick mentioned above, since coefficient of static friction is always greater than the coefficient of kinetic friction for any 2 surfaces).
Yet, when I was thinking about this technique, I wondered why it would make any difference at all. Is kinetic friction coming into play at all? The wheels are not being dragged along the rails, they are rolling. With respect to the metal surface of the rail, the wheel is not moving. So why would this make a difference if the railroad operators do their nice trick as mentioned above?
In other words, when anything round is rolling, is kinetic friction at work or is it solely static friction since the rolling object isn't sliding.
Thanks for your help.
-Nick
Yet, when I was thinking about this technique, I wondered why it would make any difference at all. Is kinetic friction coming into play at all? The wheels are not being dragged along the rails, they are rolling. With respect to the metal surface of the rail, the wheel is not moving. So why would this make a difference if the railroad operators do their nice trick as mentioned above?
In other words, when anything round is rolling, is kinetic friction at work or is it solely static friction since the rolling object isn't sliding.
Thanks for your help.
-Nick