Why do spinning tops and proton spins precess?

Question

Please can you explain the concept of precession. Why do protons in a magnetic field that are 'off balance' start to precess?

Are the protons in my body precessing right now?

Answer 1

Let's look at the top first since the proton is fairly similar.

Suppose you have a rapidly spinning top that is not perfectly oriented up and down. Then gravity will produce a torque on this top. It turns out that when you look at the equations of rotational motion, this torque causes the axis of spin to move in a circle which is parallel to the ground.

Essentially the same thing happens with a proton in amagnetic field. The field produces the torque, which causes the orientation of the spin of the proton to change. In both cases, that change in oritentation is called precession.

Another situation that arises is that of the earth. The gravity from the sun causes a slight torque on the earth, so the spin axis changes over time. In the case of the earth, this change is slow: it takes alost 20,000 years for the axis to go around in a circle once. This is called precession of the equinox.

Answer 2

Yes . The reason is that the top is lossing mass due to friction. The electrons a protons in an atom continously change mass. The precession of the atomic components is very rapid. and changes as a function of the atom's temperature.