Floating Density Ball

Floating Density BallFloating Density Ball: A hollow metal sphere that floats in cool water and sinks in warm water making the abstract concept of thermal density change immediately visible and memorable. The ball's density is precisely calibrated to sit at the boundary: cold water is dense enough to support it; warm water, less so. A simple, powerful demonstration requiring minimal setup. How to run the demonstration: Fill one 1000 ml beaker with cold water (ice water or

Floating Density Ball:

A hollow metal sphere that floats in cool water and sinks in warm water — making the abstract concept of thermal density change immediately visible and memorable. The ball's density is precisely calibrated to sit at the boundary: cold water is dense enough to support it; warm water, less so. A simple, powerful demonstration requiring minimal setup.

How to run the demonstration:

• Fill one 1000 ml beaker with cold water (ice water or refrigerated) and one with tap water at room temperature
• Record the temperature of each beaker using a thermometer before placing the ball
• Place the density ball in the cold water — observe it floating at the surface
• Transfer the ball directly to the warm water — observe it sinking
• Discuss how the same ball behaves differently due to the change in water density caused by temperature
• Extend the experiment by gradually warming the cold water and recording the temperature at which the ball transitions from floating to sinking

 The demonstration

Specifications

Suitable for primary and secondary science classrooms, this apparatus supports curriculum outcomes around density, buoyancy, the particle model of matter, and the thermal properties of water. The demonstration can also prompt discussion of real-world phenomena such as ocean thermal stratification, the water cycle, and why ice floats.

SKU: SE.MS0017-01

INSTRUCTIONS

Equipment Supplied

• Hollow metal density ball (⌀ 4 cm)
• Instruction sheet

Required — not included

• 1000 ml beaker
• Thermometer
• Cold water (ice water or refrigerated)
• Tap water at room temperature

Safety

⚠ Supervision required

Must be used under appropriate adult or teacher supervision. Not suitable for unsupervised student use, particularly when hot water is involved in extended investigations.

✕ Safety precautions advised

Take appropriate precautions when handling warm or hot water. Ensure beakers are stable on a flat surface. Follow your institution's standard laboratory safety procedures.