Why is increasing entropy sometimes referred to as "the arrow of time"?

Here's my pick at this:
Entropy (or some form of disorder) will always increase in time.

Thus if you look at snapshots of a system and see that it's entropy is increasing you can tell the flow (or arrow) of time!

Search '2nd Law of thermodynamics' for more info! :)

Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other

Athermometer to measure the temperature of course