What do 'idealised body' and 'internal structure' mean for particles?

[manimaran1605]

A red a book in classical mechanics , the author says A particle is an idealised body that occupies only a single point of space and has no internal structure clarify me these terms Idealised body and Internal structure

 

[Khashishi]

I disagree with that definition. Idealised body doesn't mean anything special. Internal structure means what it is made of or what is inside. An atom has internal structure because it is made of electrons and a nucleus. The internal structure of a nucleus is protons and neutrons.
Protons are made of quarks. But it's silly to say a proton is not a particle. Of course it is. So that definition is wrong.

A particle is something that you can count. Quantized lumps of energy. I don't know of a better definition.

 

[Nugatory]

I disagree with that definition.

OP was asking in the context of classical mechanics, and in that context the definition is just fine.

Loosely speaking, an idealized body with no internal structure is one with no spatial extension (we can say that it is at a single point in space, as opposed to something like a bacterium, which occupies a volume of space a few microns wide), and "no internal structure" means that we cannot divide the body into smaller components that we can analyze separately.

 

[Khashishi]

A fundamental particle cannot be divided further. A composite particle is something that is composed of smaller parts, but can be treated as a single object. By single object, I mean the parts are all bound together, so the group can move around as a unit.