The buoyant force (Fb) of the water pushing up on the object.This is the weight of the object - its mass time the acceleration due to gravity (9.8 ms -2 on Earth). The force of gravity (Fg) pulling down on an object.Three-quarters of an object with a density of 0.75 g/cm 3 will be submerged.Īnother way to look at the buoyancy of an object is as an interaction between two forces. An object with a density of 0.5 g/cm 3 will sit half in and half out of the water. The closer its density is to 1 g/cm3, the more of it will sit below the water level. In the case of water, an object with a density less than 1 g/cm3 will float. P>Whether an object will float or sink is dependent on its density, and on the density of the liquid it is placed in. If its volume is less than 25.2 cm 3, it will not stop before its entire volume sinks below the surface. If the object has a volume greater than 25.2 cm 3, it will stop sinking before it is completely submerged. The 2 g object will displace 2 cm 3 of water.Īn object with a mass of 25.2 g will displace 25.2 cm 3 of water. Therefore, the 1 g object will displace 1 cm 3 of water. This behavior is independent of each object's size and shape. A 2 g object will sink until it displaces 2 g of water. A 1 g object will sink until it displaces 1 g of water. The more mass an object has, the further it sinks. Specifically, when placed in water, an object sinks into the water until it displaces an amount of water equal to its own mass. All objects, even those that float, displace some water. Observing an object placed in water helps illustrate now an object's density influences its buoyancy. P>The standard metric unit for density is grams per cubic centimeter (g/cm 3). Density is the mass of an object per unit volume: The relationship between an object's volume and mass is called its density *. To determine an object's buoyancy, both its mass and volume * must be known.
An object that sinks is negatively buoyant. An object that floats in water is said to be positively buoyant. The buoyancy of an object is its tendency to float on or rise in a liquid. The ability of an object to float depends on its buoyancy. If it were, we could not explain how a giant ocean liner floats while a small pebble sinks. While weight *, or more properly, mass * does play a role, it is not the only factor. When asked why do some things float and others sink, the first thing that comes to many people's minds is the weight * of each item.