In this analogue demonstration of Rutherford’s alpha particle scattering experiment, an aluminum pinnacle represents the atomic nucleus. Ball bearings, representing alpha particles, are rolled toward the pinnacle and are deflected in patterns that match Rutherford’s scattering theory, enabling students to visualize the discovery of the nucleus.

1. Construct a raised aluminum obstacle (the pinnacle) shaped so that its cross-section represents the potential energy curve of a repulsive electrostatic interaction. Alternatively, use the base of a wine glass.
2. Place the pinnacle on a smooth horizontal surface such as a tray or table.
3. Roll ball bearings (representing alpha particles) toward the pinnacle from different approach directions and with varying impact parameters.
4. Observe how the ball bearings are deflected by the shape of the obstacle.
5. Record scattering angles and compare them to predictions from Rutherford’s scattering theory.

Beyond the Atom: Rutherford Scattering with Marbles - Perimeter Institute for Theoretical Physics:

📄 A Rutherford alpha particle scattering analogue - IOP Science: https://iopscience.iop.org/article/10.1088/0031-9120/3/4/002

• Use different sizes or masses of ball bearings to test if scattering patterns change.
• Try changing the slope or curvature of the obstacle to model stronger or weaker nuclear repulsion.
• Set up multiple obstacles to explore the effect of multiple scattering events.

• Ensure the rolling surface is stable and level to prevent ball bearings from falling to the floor.
• Keep ball bearings away from small children to avoid choking hazards.
• Take care when constructing the aluminum obstacle to avoid sharp edges.

• How does this model demonstrate the concept of the nucleus being a small, dense region within the atom? (The ball bearings are deflected sharply only when they come very close to the pinnacle, just as alpha particles are deflected when they pass near the nucleus.)
• Why are most ball bearings not deflected strongly? (Most alpha particles pass through the atom without approaching the nucleus closely, as most of the atom is empty space.)
• How does the angle of deflection depend on the distance of closest approach? (Closer approaches produce larger deflections, consistent with Coulomb’s law.)
• What limitations does this mechanical analogue have compared to real atomic scattering? (It cannot model quantum effects, attraction, or the three-dimensional nature of real scattering.)