When we want to speed up an object we give it energy. As special relativity tells us energy and mass are equivalent(E=mc2).Then some of this energy is transferred into mass, increasing the rest mass.
The Earth has its own magnetic field , it acts like there is huge bar magnet buried inside,but this bar magnet is not on the earth rotational axis it is shifted by some angle.The south of the bar magnet is on the magnetic north and the south polarity is on the magnetic north(image).As opposite polarities attract the magnetic needle (north) is attracted to the south polarity in the magnetic north.That’s why the needle always points north.If you want to know “why earth has magnetic field?”go to letter E.