Orange Buoyancy Experiment
You’ll need: a tall glass vase or a large bowl, an orange and water
Instructions: fill the container with water, and ask your kids whether they think the orange will float or sink. Why? Are they surprised when it floats? Next, peel the orange, and ask them what might happen when it’s placed back in the water. It sinks! Chances are your kids will be confused by the results.
The orange is being acted upon by two forces: gravity pulls it down and buoyancy pushes it up. Archimedes’ Principle determines the strength of the buoyant force of an object, saying that any object in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object. The orange’s peel adds much more volume (so more fluid is displaced) but adds only a small amount of mass to be acted upon by gravity. When the peel is removed, the orange’s volume decreases, so the buoyant force decreases, while the orange’s mass, and thus gravity’s strength, remains the same. This allows gravity to overcome the buoyant force and causes the orange to sink!
Experiment and Photo via Playdough Plato