What are subatomic particles that are responsible for most of an atom's mass?

Question

pleassse help me!

Answer 1

"Protons and neutrons" is probably the correct answer.

As one answerer noted, the protons and neutrons are themselves composed of quarks. However, note that the mass of a proton or neutron is in excess of 900 MeV/c^2, whereas up and down quarks have masses which are almost certainly less than 10 MeV/c^2. Given that there are three quarks per proton/neutron, this is certainly confusing. You need some advanced physics (way above my head) to explain why this occurs. In any case, it is not actually correct for this reason to say that quarks make up most of the mass of an atom.

Edit: @ PhysicsDude: You are certainly correct in stating that I don't understand any of the physics necessary to give an explanation of quark masses and hadron masses (give me a break, I'm only 15), but it seems that our disagreement has a philosophical basis; it is not a question of the physics itself (for, I do acknowledge that you understand the subject far better than I do.)

Your argument seems to be based on the idea that the quarks are the only real elementary particles found within the atom's nucleus where >99.9% of the atom's mass is concentrated,  therefore, they are responsible for the mass of the nucleus.

My argument is that the masses of the protons and neutrons are a result of the complicated interactions of QCD (of which, again, I gladly admit to complete ignorance), and that if the numbers quoted as quark masses are not directly relevant, then it doesn't make sense to say that quarks are responsible for most of the mass of the nucleus.

I had no intention of implying that I understand the underlying physics better than you do. Rather, from the philosophical point of view, we disagreed on the meaning of the word "responsible". Still, I am sure that if this was a homework question from a high-school course, the answer is "protons and neutrons".

Best regards and a humble apology,

  --Brian

Answer 2

Protons and Neutrons.

Good luck.

Answer 3

just the protons and neutrons the electrons weigh barely anything

Answer 4

Actually, the answer is "Up" and "Down" quarks, since protons and neutrons are NOT true elementary particles like the electron. They are composites made of Quarks, which can not be broken down further into more fundamental units.

So the answer to your question is: quarks are responsible for most of an atom's mass.

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Listen Brian, it is clear that you don't know what you're talking about. Due to hadronization (i.e. confinement), quark masses cannot be measured directly and must be inferred from the effects they have on their parent hadron's (i.e. proton or neutron) properties. In addition, the mass of the proton or neutron is NOT just a simple sum of the 2 up quarks and 1 down quark masses. To understand how to calculate quark masses, one must use the quark model through chiral perturbation theory. The absolute values of the masses are currently determined from QCD sum rules (also called spectral function sum rules) and lattice QCD.

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Brian, I accept your apology, and I also apologize for my apparent rudeness in the terse way I replied to your answer.

However, I must emphasize that this is not a philosophical disagreement over the "responsible" party. There is NO such thing as a proton or a neutron. These are artifacts (or labels) created by humans due to the lack of ability to resolve objects at the sub-atomic scale. Quarks, like electrons, are real elementary particles that do not breakdown further into more fundamental components.

The answer to this question is quarks no matter how you slice it.