Slide 1
Floating is a force balance
Water exerts an upward buoyant force on an immersed object. A freely floating object settles where that force balances its weight.
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At equilibrium the object is not accelerating vertically. If it is pushed downward and displaces extra water, the buoyant force can exceed its weight and drive it back upward.
Slide 2
Count the displaced water
The buoyant force equals the weight of fluid displaced by the object. It depends on immersed volume and fluid density.
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A fully submerged litre of volume displaces a litre of water regardless of whether the object is wood or metal. Its own weight determines whether the resulting upward force is enough to support it.
Slide 3
Average density matters
A hollow vessel can float even when its shell material is denser than water. The vessel’s overall mass is spread across a larger volume.
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Water entering the hollow space adds mass without preserving the same excluded volume. This can destroy the favourable average-density balance, which is why watertight compartments matter to a vessel’s buoyancy.
Slide 4
Different fluids change the balance
A denser fluid provides more buoyant force for the same displaced volume. A floating object then needs to immerse less volume.
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A hydrometer uses this principle: its depth of immersion varies with liquid density. The scale converts that change into a reading, and temperature matters because liquid density can change as it warms.
Slide 5
Floating also needs stability
Balancing weight and buoyancy prevents vertical acceleration, but does not by itself prevent tipping. Their lines of action determine the turning effect.
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When a vessel tilts, the shape of displaced water changes and its buoyant force can shift sideways. Whether that shift restores the vessel or overturns it depends on geometry and mass distribution.