The Cosmic Classroom - Fusion, Fission, and Why Not Iron?

What is the difference between nuclear fusion and fission? Why can't stars fuse iron?

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  Education

[Jun Y]

Hi thanks for your great video！ I have little question, I did not get the idea about in the end of the video, you said "so you can get release by fusing elements that are ligthter ? than Fe and building blocks that are bigger. or you can star from elements that are much heavier than iron" lighter&heavier, you mean atomic weight not atomic mass right? thanks a lot.

[Vera Margoniner]

I am speaking of general trends in atomic behavior so it doesn't matter here. But I suppose if you have a sample with all kinds of isotopes for an atom the atomic weight would be more precise.

[Jun Y]

thanks!

[Jun Y]

C=12 that's the atomic weight, due to isotope.

atomic mass: by definition, the mass of one proton is the mass of the nucleus of Carbon divided by 12. so the atomic mass of the Carbon is 1.

just for He, atomic mass almost equal to atomic weigh =4.

[jakubciazela]

Probably the given carbon mass is wrong. I think it should be 12.0000. Then we have 12.0078 > 12.0000

[Reza Nouri]

hello there.

first of all i wanted to thank you for your video. i'm not a student but i found it interesting. during the fussion section i noticed that you said "3 He atoms make a carbon and mass will change in to energy" when i looked at the 3 He mass i found that it is less than a Carbon mass. who is it possible? or is my calculation wrong?

mass of 3 He =3*4.0026=12.0078

mass of 1 C = 12.0110

this calculation according to your video shows that something is wrong

[ExNihiloJimmy]

great video

thankyou