Rotation of Rigid Body: Analyzing Classical Mechanics

In summary, In the framework of Classical Mechanics, we can distinguish translation from rotation in a rigid body and should only pay attention to rotation. The most complicated motion is rotation with a fixed point, and the rotation of the Earth can be considered an inertial motion due to the largest density being in the center. However, when considering the spin of elementary particles, it must be treated according to quantum mechanics and is an intrinsic property that cannot be changed. The origin of spin is unknown and it is already present, similar to the charge of any elementary particle. Rotation also has thermodynamic effects, such as friction and heat generation, and can impact the rotation of other bodies.
  • #1
zhangyang
58
0
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.
 
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  • #2
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.
 
  • #3
andrien said:
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?
 
  • #4
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.
 
  • #5
Angular momentum is a form of inertia.
 

1. What is a rigid body?

A rigid body is an object that maintains its shape and size even when subjected to external forces. This means that the distances between different points on the object remain constant.

2. What is rotation of a rigid body?

Rotation of a rigid body refers to the motion of the body around a fixed point called the axis of rotation. This motion can be described by its angular displacement, velocity, and acceleration.

3. What is the difference between rotational and translational motion?

Rotational motion involves movement around a fixed point, while translational motion involves movement from one point to another in a straight line. In rotational motion, all points on the body move in circular paths, while in translational motion, all points move in parallel paths.

4. How is the rotational motion of a rigid body analyzed in classical mechanics?

In classical mechanics, the rotational motion of a rigid body is analyzed using principles such as Newton's laws of motion, torque, and angular momentum. These principles help determine the motion of the body and the forces acting on it.

5. What is the importance of understanding the rotation of a rigid body in scientific research?

The rotation of a rigid body is important in many areas of scientific research, such as mechanics, engineering, and astronomy. It allows us to understand the motion of objects in our world and the forces that act on them, leading to advancements in technology and exploration of the universe.

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