Why does the magnet have a magnetic force, that is, the earth's magnetic field and current will be strongly combined due to the rotation of the earth, and finally the whole earth becomes a large magnetic field. Minerals such as nickel, cobalt, and iron on Earth rotate as the Earth rotates, turning it into a natural magnet. Everyone knows that there is a gravitational field between the substances. Similar to a magnetic field, it is a field that fills the space around the pole. The size of the magnetic field can be represented by the number of imaginary magnetic lines of force. The denser the magnetic field lines are the stronger the magnetic field, and the weaker the magnetic field is.