The air inside changes the apple’s average density
An apple is not a solid block of fruit. Its cells are packed with watery tissue, but small spaces between cells hold air. That air adds volume without adding much weight, lowering the density of the apple considered as a whole. The key is the average: the apple’s flesh can be mostly water and still be less dense overall than the water around it.
Floating is a balance of forces
When an apple enters water, it pushes water out of the way. The water pushes back upward; this buoyant force grows as more of the apple goes under. The apple settles when the upward push from the displaced water matches the apple’s weight. Because its average density is lower than water’s, that balance is reached while part of the fruit remains above the surface.
The same principle explains why an object with hollow spaces can float even when its solid material would sink. In an apple, the air is distributed through the fruit’s structure rather than collected in one large cavity. Those tiny spaces help the whole fruit displace enough water to support its weight—one reason apples can bob at the surface instead of dropping to the bottom.
