In science, matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energy or force-fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Matter constitutes much of the observable universe, although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined. It is normally defined as anything that has mass and takes up space.
<xml><o></o>
Matter can be in five different states: solids, gas, liquid, plasma, and the Bose-Einstein condensate.<o></o>
Definition:<o></o>
Anything which occupies space and has mass is known as matter. In physics, there is no broad consensus as to an exact definition of matter. Physicists generally do not use the saying when precision is needed, preferring instead to speak of the more clearly defined concepts of mass, energy, and particles.
<o></o>
A possible definition of matter which at least some physicists use is that it is everything that is constituted of elementary fermions. These are the leptons, including the electron, and the quarks, including the up and down quarks of which protons and neutrons are made. Since protons, neutrons and electrons combine to form atoms, molecules and the bulk substances which they make up with all matter. Matter also includes the various baryons and mesons. Things which are not matter include light (photons) and the other gauge bosons.<o></o>
However, this definition is not always satisfying when examined closely. In particular, under this definition, there are things may have mass without being matter, like:<o></o>
1.
W and Z bosons
have mass, but are not elementary fermions.
<o></o>
2.
Any two photons which are not moving parallel to each other, taken as a system, have an invariant mass.
<o></o>
3.
Glueballs have mass due to their binding energy, but contain no particle with mass, nor any elementary fermions.
<o></o>
And also there are matters without mass, like:<o></o>
1.
Most of the mass of protons and neutrons comes from the binding energy between the quarks, not the masses of the quarks themselves. <o></o>
2.
One of the three types of neutrinos may be mass less.<o></o>
Quarks combine to form hadrons. Because of the principle of color confinement which occurs in the strong interaction, quarks never exist unbound from other quarks. Among the hadrons are the proton and the neutron. Usually these nuclei are surrounded by a cloud of electrons. A nucleus with as many electrons as protons is thus electrically neutral and is called an atom, otherwise it is an ion.
<o></o>
Leptons do not feel the strong force and so can exist unbound from other particles. On Earth, electrons are generally bound in atoms, but it is easy to free them, a fact which is exploited in the cathode ray tube. Muons may briefly form bound states known as muonic atoms. Neutrinos feel neither the strong nor the electromagnetic interactions. They are never bound to other particles.<o></o>
_________________
"عزيزي العضو دعنا نأخذ بأيد بعضنا البعض لنخلق جوا من التفاعل،، بدل الإكتفاء بوضع مساهماتنا والتعليق عليها فقط،، دعنا نقرأ لبعضنا البعض ونحضر مساهمات بعضنا البعض ليزيد التفاعل ونخلق لأنفسنا حيزاً بعيداً عن الشكر والمجاملات لننتقد وننقد حتى تصبح أقلامنا شعلة من نور ينير ظلمة الملل والركود .......اي مشكله تواجهك عزيزي الزائر اضاف المدير العام علي الماسنجر
b_almehman@hotmail.com
**************
للشكوى أو الأستفسآر
b_almehman@hotmail.com
