In physics, a physical body (sometimes called simply a body or even an object) is a collection of masses, taken to be one. For example, a cricket ball can be considered an object but the ball also consists of many particles (pieces of matter).

In classical physics, mechanics, quantum physics, and cosmology

A physical body is an object which can be described by the theories of classical mechanics, or quantum mechanics, and experimented upon with physical instruments. This includes the determination of position, and in some cases the orientation in space, as well as means to change these, by exerting forces.

In classical physics, a physical body is a body with mass, not only energy, is three dimensional (extended in 3-dimensions of space), has a location or position in space, and is lasting for some length of time. It is the subject of study in an experiment and is the object referred to in a law of physics, or physical theory. It can be considered as a whole, but may be composed of a collection of smaller physical bodies, e.g. a weight, ball, proton, or planet. As such, a physical body always has extension in physical space.

For instance, the force of gravity will accelerate a body if it is not supported, thus causing a change of its position (that is, it falls freely). However, it should be noted that it is not necessary for there to be forces present for an object position to change - only the rate of change of the object's position, that is, its velocity, will change under the influence of forces.

But in Quantum physics and Cosmology, there is a debate as to whether some elementary particles are not bodies, but are mere points without extension in physical space within space-time, or are always extended in at least one dimesnion of space as in String theory or M theory.

In biology

A human's, animal's or vegetable's physical body is made up of organs and tissues and is a part of the total living being which in the human being may also include a psychological or spiritual component. However, whether or not a human being includes a spiritual component is entirely up to philosophical debate and faith.

In psychology

In some branches of psychology, depending on school of thought, a physical body is a physical object with physical properties, as compared to mental objects. In behaviorism, a phsyical body and its properties are the only meaningful objects of study. In cognitive psychology, physical bodies as they occur in biology are studied in order to understand the mind, which may not be a physical body, as in functionalist schools of thought.

In philosophy

A physical body is a thing that is a concrete physical object, which exists in and is extended in the physical world of physical space, e.g. as studied by physics. Examples are a cloud, a human body, a weight, a billard ball, a table, or a proton. In most philosophies, a physical body is not a mental object in the mental world, not an abstract object as in a the world of Platonic ideals, and not a mathematical object; e.g., not a sense datum, idea, concept, or set. More concrete specific contrasting examples that are not physical bodies are emotions, an object in the visual field, the concept of "justice", a feeling of hatred, or the number "3". In some philosophies, like the Idealism of Berkeley, a physical body is a mental object, but still has extension in the space of a visual field.

In new age philosophy, mysticism and religion

In some systems of mysticism, such as Theosophy, the physical body is understood as the last of several progressively denser "vehicles of consciousness". In Blavatskyian Theosophy it is called by the Vedantic name sthula sarira - "gross body" - and distinguished from the linga sarira, the "subtle body" or astral double. In C. W. Leadbeater and Alice Bailey, the physical body is distinguished from the etheric body, which serves as its "blueprint", and structures of the etheric body, such as chakras, are mirrored in the main glands and nerve ganglia of the physical body.

In some religions, and in some new age philosophies, a physical body is contrasted with the self, mind, spirit, soul, or astral projection, and sometimes with an heavenly body. It is ephemeral in time, not eternal. It may be what houses the spirit or soul, and it is what is left behind in an astral projection, or ascention into heaven. A physical body exists on earth, not in heaven, not in the astral world, nor in the aether.

• Annie Besant, "Theosophy" online
• H.P. Blavatsky, The Key to Theosophy

See also

• Deformable body
• Rigid body
• Human body

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