The needle on a compass always points in the direction of magnetic north because of the magnetic poles of earth. the compass is essentially a magnet itself, so the southern pole of the compass is attracted to the northern pole of earth.
You use energy from your body and press the pedals on the bike that has chains and the chains are connected to a circular ish shape and is also connected to the wheel and it spins
First we need to convert the angular speed from rpm to rad/s. Keeping in mind that


the angular speed is

And so now we can calculate the tangential speed of the child, which is the angular speed times the distance of the child from the center of the motion:
Mechanical or Electromagnetic