# Rotation of rigid body

zhangyang
In the framework of Classical Mechanics,there is no problem in the rotation of rigid body.But I want to make the concept about rotation more clear.

About rigid body ,there is no vibration;it would only rotate and translate.We can easily distinguish translation from rotation in rigid body.Certainly we should only pay attention to rotation.

The most complicated motion is the rotation with a fixed point.so let us discuss the rotation with a fixed aixs first.Because the point fixed rotation has its axis every time.Because the shape of rigid body can’t be changed.

My question is :could the rotation be a inertial motion?

Let us consider the spin of the Earth.What does the original energy of spin come from,why would the spin continue forever?We know that every point of Earth except the centre is in a circular motion ,so they are not in a inertial motion.Someone will say that it is same as the rotion of Earth round the Sun.But it isn’t the same.Because there is only gravity between Earth and Sun,but gravity and electromagnetism between the point of Earth and the center of the Earth.The unique explanation is that :the largest density of Earth is in the center.So,we can consider the spin as a inertial motion.

But if I am going to the spin of electron,what is the answer?And could we say that everything in the world is rotating with its own axis?Since every particle has its spin ,we can confess that opinion.

All above,we haven’t consider the thermodynamical effect of rotation.If we now consider ,we will find that rotation must meet friction and generate heat.So we shouldn’t confess the eternal rotation of a particular body.Maybe the energy lost from it will make the other rotation accelerate.Since the thermodynamical process is universal ,the spin of elementary particle is also governed by the law of thermodynamics.

andrien
elementary particles do not rotate.The spin is their intrinsic property,it can not be changed.Electron is spin 1/2,it will always be spin 1/2.The most you can do is to flip the spin of electron by applying a radio frequency when there is already a constant magnetic field,which will separate energy levels by h(bar)w.where w is written in terms of constant magnetic field.

zhangyang
elementary particles do not rotate.The spin is their intrinsic property,it can not be changed.Electron is spin 1/2,it will always be spin 1/2.The most you can do is to flip the spin of electron by applying a radio frequency when there is already a constant magnetic field,which will separate energy levels by h(bar)w.where w is written in terms of constant magnetic field.

What is the origin of spin of elementary particles?If it can't be changed,how could it be generated?

andrien
spin of elementary particles must be treated according to quantum mechanics.There is no reason for it's generation,it is already there just like charge of any elementary particle.

Ryoko
Angular momentum is a form of inertia.