Monday, August 20, 2012

A little puzzle

I set my cell phone display-up on a flat surface (a table) and I turn on Google Maps.  I rotate the phone so that it "points north" (that is, the phone is on its back, the display is facing up, the top edge of the display is facing north, the left and right edges are parallel to rotation of the earth).

On Google Maps there is a little arrow-shaped icon that represents the position and orientation of the phone.  Naturally, it points at the top of the map, which is at the top of the display, and therefore the little arrow points north as well.

If I now rotate my phone slightly clockwise, what does the arrow do?

a) move in the same direction as the phone (clockwise)
b) move in the opposite direction as the phone (counter-clockwise)
c) not rotate

and how fast?

a) twice the speed as the phone rotates
b) exactly the same speed as the phone
c) half the speed as the phone rotates
d) it doesn't rotate

Try to solve this in your head, then check with your phone.