3. Snail Ball

Official Problem Statement

A hollow sphere contains a heavy ball and some viscous fluid. The rolling motion of such a sphere down an inclined plane is uneven and surprisingly slow. Explain and investigate this effect.

Suggested Experimental Procedure

Building the Lab Snail Ball

Practical approach — ping-pong ball:

1. Cut a ping-pong ball in half with a fine saw or sharp knife.
2. Place a heavy metal ball bearing (8–12 mm diameter) inside one hemisphere.
3. Bond the two halves with two-part epoxy; seal the seam completely.
4. Inject viscous fluid through a small hole using a syringe, then seal the hole.

Sample Variations for Systematic Comparison

Build several balls with identical total size and mass but different fluid viscosities:

• Pure water (~1 mPa·s)
• 50% glycerol–water mix (~6 mPa·s)
• 85% glycerol (~100 mPa·s)
• Pure glycerol (~1500 mPa·s)
• One air-only ball (reference — no fluid, no ball bearing)

Experimental Setup

1. Build an adjustable inclined plane (5°–40°) from a board and a hinge.
2. Release the ball from the top of the ramp and time it over a fixed 1 m distance.
3. Film from the side to capture the irregular rolling motion for later analysis.
4. Repeat with an ordinary ping-pong ball as a reference.
5. Plot velocity versus ramp angle for each viscosity.