Experiments you can run yourself.
Why does a nucleus emit an alpha particle even though its energy is many times smaller than the Coulomb barrier? See quantum tunnelling and the Geiger–Nuttall law — an academic extension of the topic of radioactivity.
Why do both fusion of light nuclei and fission of heavy ones release energy? See the B/A curve with its peak at iron — an academic extension of E=mc² and nuclear reactions.
How does the neutron multiplication factor k decide between dying out, a stable reactor, and avalanche growth? See N = N₀·kⁿ and the meaning of critical mass.
How does a long-lived parent "feed" a short-lived daughter, and why does the daughter's amount level off despite its constant decay? Bateman equations and secular equilibrium.
Muons live 2.2 μs, yet reach Earth from a dozen-odd kilometres up. See how time dilation (or length contraction) makes it possible — a tangible proof of special relativity.
How do you read the velocity of a receding galaxy from the redshift of its spectrum? The relativistic Doppler effect, redshift z, and the evidence that the Universe is expanding.
Gravity bends light — and 2× more strongly than Newton would allow. See the angle α = 4GM/c²b, the Einstein ring and Eddington's famous 1919 measurement.
A beam of atoms in an inhomogeneous field splits into TWO discrete beams, not a continuous spread. See spin quantisation and how measurements along different axes fail to commute.