Idea 2of 7Builds onSame element, different nucleusThe total never changes
Mass is the fuel
A nucleus pays out energy. With what?
Today you'll discover
- what a nucleus spends when it gives off energy
- why the pieces afterward weigh a sliver less
- the equation that prices the sliver
Think firstA nucleus rearranges itself and throws out energy
A nucleus rearranges itself and throws out energy. What paid for it?
Decide first, then press Next. Compare the mass before with the mass after.
A single nucleus drawn as a cluster of warm and cool balls. After a prediction, rays leave it, then the cluster afterward is shown a sliver lighter, then a ledger of bars compares the mass before, the mass after and the energy out. The last step asks whether the Sun gets lighter as it shines.
See the whole ideathe big idea and the key word, in one place
The big idea
A sliver of mass becomes a flood of energy.
Why it happensThe ledger still balances: the energy out equals the mass lost times c squared. Mass was always a form of energy; the nucleus is where enough of it changes to notice.
Key word
- mass–energy equivalence
- mass and energy are interchangeable: a mass m is equivalent to an energy E = m c², where c is the speed of light
About this modelNuclei are drawn a million times too large relative to the atom, and the energy rays are a symbol, not a picture of light.
Nuclei are drawn a million times too large relative to the atom, and the energy rays are a symbol, not a picture of light.
Ready to use it?
- Explain where the energy of a nuclear change comes from, and find it from the mass lost.