Understand upthrust (buoyancy) and how it competes with gravity to determine if an object floats or sinks.
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Diagram of an object in water with upward and downward force arrows.
A closed plastic bottle partially submerged in a bucket of water. A downward red arrow labeled 'Gravitational Force (Wei…
Introduce upthrust / buoyant force.
The Earth's gravity pulls everything down towards its center. So why do some things, like a plastic bottle or a wooden boat, float on water instead of falling to the bottom?
When you place an object in a liquid, the liquid actually fights back against gravity. It applies an upward push on the object.
Explain the rules of floating/sinking and Archimedes Principle.
Whether an object floats or sinks is simply a tug-of-war between two forces.
When an object enters a liquid, if its downward gravitational force (weight) is greater than the upward buoyant force, the object sinks. However, if the two forces are equal, the object happily floats.
MCQ on weight vs upthrust.
A metal coin is dropped into a glass of water and sinks straight to the bottom. What must be true about the forces acting on the coin?