Why do objects float on the surface of water?

Objects float on the surface of water primarily due to a principle discovered by Archimedes, which involves two main forces: buoyancy and gravity (weight), and the concept of density.

1. Gravity (Weight): Every object has weight, which is the force of gravity pulling it downwards towards the center of the Earth.

2. Buoyancy (Upthrust): When an object is placed in a fluid (like water), the fluid exerts an upward force on the object. This upward force is called buoyancy or upthrust.

• Archimedes' Principle states that the buoyant force on an object submerged in a fluid is equal to the weight of the fluid that the object displaces.

Why an object floats:

An object floats if the upward buoyant force exerted by the water is greater than or equal to the downward force of its own weight.

The role of Density:

Density is a key factor in determining whether an object floats or sinks. Density is defined as mass per unit volume (Density = Mass / Volume).

If an object's average density is LESS than the density of water:

• The object displaces a volume of water that weighs more than the object itself.
• Since the buoyant force equals the weight of the displaced water, the buoyant force will be greater than the object's weight.
• The object will float. (e.g., wood, ice, a hollow boat)

If an object's average density is GREATER than the density of water:

• The object cannot displace enough water to create a buoyant force equal to its own weight.
• The buoyant force will be less than the object's weight.
• The object will sink. (e.g., a rock, a solid piece of steel)