It floats if it is less dense than water. When you drop a marshmallow in water, it floats like a balloon. A marshmallow is full of air bubbles, which puff it out. The sugar in the marshmallow gets spread out over a large area, making the marshmallow less dense than water.

Objects like apples, wood, and sponges are less dense than water. They will float. Many hollow things like empty bottles, balls, and balloons will also float. That’s because air is less dense than water.

An object floats when the weight force on the object is balanced by the upward push of the water on the object. If the weight force down is larger than the upward push of the water on the object then the object will sink. If the reverse is true then the object will rise – rising is the opposite of sinking.

The wood ball floats because wood’s lower density makes the wood ball lighter than the same volume of displaced water.

Obviously heavy woods do not float on water. The heaviest woods with specific gravity higher than 1 are usually hardwoods from either desert or tropical places. Rosewoods and ebonies are often heavy enough to sink. Lignum vitae, desert ironwood, African blackwood, ipe and other woods like these are heavy woods.

Wood, cork, and ice float in water because they are less dense than water. It floats because it weighs less than amount of water it would have to push out of the glass if it sank. Wood, cork, and ice are all less dense than water, and they float; rocks are more dense, so they sink.

Teak does not rot. Most hardwoods rot after being saturated with moisture for long periods of time. Because of its density, teak will float on the surface of water.