Magnets attract iron. Why does gravity attract everything?

Electromagnetic force and gravity are two different forces, which are destined to act on different objects.

Physically, everything Force? Can be classified into four major contacts, all of which are real in our lives? Force? Except gravity, it is essentially electromagnetic interaction, such as friction, tension, elasticity, pressure and so on.

electromagnetic force

Magnetic force is essentially electromagnetic interaction, which can be described by Maxwell equations. Magnets can attract metals such as iron, cobalt and nickel because these substances belong to ferromagnetic substances.

Principle:

(1) We know that almost all common substances are composed of atoms;

(2) The electrons outside the nucleus move around the nucleus, so the moving charge generates a magnetic field, and some substances may have the situation that the net magnetic moment of a single atom is not zero;

(3) In general, the arrangement of magnetic moments in a substance is irregular, resulting in zero magnetic moment of the whole substance;

(4) But for ferromagnetic substances, there will be interaction between adjacent atoms, and then many adjacent atoms will be formed? Magnetic domains Each magnetic domain varies from a few microns to a few millimeters, just like a small magnetic needle;

(5) The directions of these large and small magnetic domains are random, and they are not magnetic as a whole without external force; Once there is an external magnetic field, these magnetic domains seem to be commanded, and the magnetic moments are biased in the same direction, and then the whole becomes magnetic and attracted by magnets;

(6) When the external magnetic field is removed, the magnetic moment direction of some magnetic domains may not decrease, so the whole magnetic field is weak, so we say that iron is magnetized;

(7) When ferromagnetic substances are heated, the thermal motion of molecules becomes intense. When the kinetic energy of thermal motion is greater than the interaction energy between adjacent atoms, ferromagnetic substances will be transformed into paramagnetic material. At this time, the response to the external magnetic field is weak, indicating that it is no longer attracted by the magnet. This critical temperature is called. Curie point? ;

For example, there is a ferromagnetic substance at the bottom of the rice cooker at home, and its Curie point is generally 103℃. When the water in the pot is boiled dry, the temperature in the pot rises to 103℃, and the substance is no longer attracted by the electromagnet to produce action, thus disconnecting the heating power supply.

universal gravitation

In classical mechanics, the magnitude of gravity depends on the distance and mass of matter, which is the famous law of universal gravitation, and it also shows that all matter with mass will produce gravity.