Mass and energy are equivalent, as described by Einstein's famous equation E = mc². This principle underlies nuclear energy, particle physics, and cosmology.

Key Formulas:

• E = mc² - Energy from mass
• m = E / c² - Mass from energy

Units:

• Mass: kg, g, MeV/c²
• Energy: J, kJ, MJ, eV
• c: m/s (speed of light)

Applications:

• Nuclear reactions and fission/fusion
• Particle physics and accelerators
• Astrophysics and cosmology
• Radioactive decay