Turntable Paradox

A solid ball placed on a rotating turntable does not simply slide or fly off. Instead, it rolls and follows a spiral orbit around the axis of the turntable at a specific angular speed relative to the turntable’s motion.

1. Place a rotating turntable on a stable base with its axis vertical.
2. Gently place a solid spherical ball near the center of the turntable surface.
3. Rotate the turntable at a steady speed.
4. Observe the motion of the ball as it rolls across the surface.
5. Note how the ball follows a spiral path instead of sliding straight off.
6. Compare the ball’s angular speed with that of the turntable.

The Turntable Paradox - Steve Mould:

📄 The Turntable Paradox - C_R 3442: https://www.mapleprimes.com/posts/224435-The-Turntable-Paradox

• Try different sizes of balls.
• Use balls with different masses but similar radii.
• Vary the rotation speed of the turntable.
• Compare the behavior of a hollow sphere versus a solid sphere.
• Change the friction of the surface (rough vs smooth).

• Ensure the turntable is stable and securely mounted.
• Keep hands and loose objects away from the spinning edge.
• Avoid high rotation speeds that may launch the ball dangerously.

• Why doesn’t the ball immediately slide off the turntable? (Because rolling friction and rotational inertia redirect its motion into a spiral path.)
• What is the relationship between the ball’s orbital angular speed and the turntable’s angular speed? (For a solid sphere, the ball’s orbital angular speed is 2/7 that of the turntable.)
• How do mass and radius affect the motion? (They change the ball’s moment of inertia, influencing how easily it spins.)
• How does surface friction alter the path?
• Will the ball eventually leave the turntable? (Yes, over time frictional effects and imperfect rolling may cause it to drift outward.)