How could you predict the sinking/floating behavior of a spherical object?

To predict the sinking/floating behavior of a spherical object, you could determine its density.

Step 1. Determine its mass on a suitable balance.

Step 2. Determine its volume

Either

Measure its circumference. C = 2πr, so you can calculate r

or

Measure its diameter. d = 2r, so you can calculate r

Then

V = ⁴/₃πr³ , so you can calculate its volume.

Step 3. Calculate its density (D).

Density = mass/volume

If D < 1 g/cm³, the object will float in water. If D > 1 g/cm³, the object will sink.