buoyancy

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Illustration showing Archimedes' principle: a 5 kg weight is weighed in air, then submerged in water, where it appears to weigh 2 kg; a separate container shows 2 kg of displaced water, demonstrating buoyant force.

Why do objects float or sink in water?

Diagram showing how a ship stays upright, with arrows indicating the downward force of gravity at the center of gravity (G) and the upward force of buoyancy at the center of buoyancy (B), both in level and tilted positions.

Diagram showing a teleost fish, specifically a perch, with a side view and a labeled cross section. The cross section identifies internal structures including muscle, vertebra, neural spine, nerve cord, dorsal aorta, dorsal and ventral ribs, swim bladder, coelom, and stomach. The side view shows the location of the swim bladder and stomach inside the fish.

A bright yellow submersible explores an underwater cave, surrounded by rocks, aquatic plants, and schools of fish illuminated by blue light from above.

Hot-air balloon

Diagram showing three orientations of a uniform square prism floating in liquid of twice its density, with the stable position labeled C. Each prism is half submerged, and points B and C are marked to indicate centers of buoyancy and gravity.

How Did the Montgolfier Brothers' Hot-Air Balloon Contribute to Aviation?

Know how some spiders walk on the surface of the water

How phytoplankton function and survive in the ocean

buoyancy: Media

physics

Videos

Why do objects float or sink in water?

Why do objects float or sink in water?

Learn what determines whether an object in water will float or sink.

Video: Encyclopædia Britannica, Inc.

How Did the Montgolfier Brothers' Hot-Air Balloon Contribute to Aviation?

How Did the Montgolfier Brothers' Hot-Air Balloon Contribute to Aviation?

Hot-air ballooning from the Montgolfier brothers to the present.

Video: Encyclopædia Britannica, Inc.

Know how some spiders walk on the surface of the water

Know how some spiders walk on the surface of the water

Learn how some spiders move across the surface of water.

Video: © Open University (A Britannica Publishing Partner)

How phytoplankton function and survive in the ocean

How phytoplankton function and survive in the ocean

Learn about phytoplankton, plantlike types of microscopic algae that live suspended...

Video: Encyclopædia Britannica, Inc.

Images

Illustration showing Archimedes' principle: a 5 kg weight is weighed in air, then submerged in water, where it appears to weigh 2 kg; a separate container shows 2 kg of displaced water, demonstrating buoyant force.

Archimedes' principle of buoyancy

Here, a 5-kg object immersed in water is shown being acted upon by a buoyant (upward)...

Encyclopædia Britannica, Inc.

Diagram showing how a ship stays upright, with arrows indicating the downward force of gravity at the center of gravity (G) and the upward force of buoyancy at the center of buoyancy (B), both in level and tilted positions.

Buoyancy in ships

The weight of a ship acts through the ship's center of gravity (G). It is counteracted...

Encyclopædia Britannica, Inc.

Diagram showing a teleost fish, specifically a perch, with a side view and a labeled cross section. The cross section identifies internal structures including muscle, vertebra, neural spine, nerve cord, dorsal aorta, dorsal and ventral ribs, swim bladder, coelom, and stomach. The side view shows the location of the swim bladder and stomach inside the fish.

Fish swim bladder

The swim bladder expands and contracts so that a fish may achieve buoyancy.

Encyclopædia Britannica, Inc.

A bright yellow submersible explores an underwater cave, surrounded by rocks, aquatic plants, and schools of fish illuminated by blue light from above.

A submarine

Submarines use ballast tank technology to increase and decrease their density.

© MATJAZ SLANIC—E+/Getty Images

Hot-air balloon

Hot-air balloon

A hot-air balloon is prepared by heating the air inside the balloon.

© docksnflipflops—iStock/Getty Images

Diagram showing three orientations of a uniform square prism floating in liquid of twice its density, with the stable position labeled C. Each prism is half submerged, and points B and C are marked to indicate centers of buoyancy and gravity.

possible orientations of a square prism in liquid

Figure 2: Three possible orientations of a uniform square prism floating in liquid...

Encyclopædia Britannica, Inc.

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