In fission, the products have less mass than the starting materials do. Why does this happen?

Explanation

### Step-by-Step Solution:

1. **Understanding Fission**: Fission is a nuclear reaction where the nucleus of an atom splits into two or more smaller nuclei, along with the release of energy. This process typically occurs in heavy elements like uranium or plutonium.

2. **Mass of Reactants vs. Products**: In a fission reaction, the total mass of the products (the smaller nuclei formed after the split) is found to be less than the mass of the original reactants (the heavy nucleus before fission).

3. **Mass-Energy Conversion**: The reason for this mass difference lies in the conversion of mass into energy. According to Einstein's mass-energy equivalence principle, expressed in the equation \(E = mc^2\), mass can be converted into energy.

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