## Archimedes' Principle

 2.5 Archimedes' Principle

 Archimedes' principle An object when partially or completely submerged in a fluid is acted on by a buoyant force equal to the weight of fluid displaced.

• Volume of water displaced = Volume of submerged objects
• Weight of water displaced = Buoyant force

 Buoyant force, $$F$$ $$F=\rho v g$$, where F = buoyant force, $$\rho$$ = density of the liquid, v = volume of liquid displaced, g = gravitational acceleration

Archimedes' principle application

1. Submarine
• Dives (move downwards)
• Ballast tank is filled with water
• Weight greater than buoyant force (W > F)
• Submarine dives downwards
• Rises (move upwards)
• Water is removed from tank
• Weight less than buoyant force (W
• Submarine moves upwards
• Constant depth @ floats
• W=F

2. Hot air balloon
• Downwards
• Temperature decrease, volume of balloon decrease
• Volume of air displaced decrease
• Buoyant force decreases
• W>F
• Upwards
• Temperature increase, volume increase
• Volume of air displaced increase
• Buoyant force increases
• W
• Constant depth
• W=F

3. Plimsoll line
• In cooler or denser water, ship floats more.
• In warmer or less dense water, ship sinks more.
• Goal: to ensure the ship is loaded within safety limit

4. Hydrometer
• In low-density liquid
• hydrometer sinks deeper
• In high-density liquid
• hydrometer floats higher

## Archimedes' Principle

 2.5 Archimedes' Principle

 Archimedes' principle An object when partially or completely submerged in a fluid is acted on by a buoyant force equal to the weight of fluid displaced.

• Volume of water displaced = Volume of submerged objects
• Weight of water displaced = Buoyant force

 Buoyant force, $$F$$ $$F=\rho v g$$, where F = buoyant force, $$\rho$$ = density of the liquid, v = volume of liquid displaced, g = gravitational acceleration

Archimedes' principle application

1. Submarine
• Dives (move downwards)
• Ballast tank is filled with water
• Weight greater than buoyant force (W > F)
• Submarine dives downwards
• Rises (move upwards)
• Water is removed from tank
• Weight less than buoyant force (W
• Submarine moves upwards
• Constant depth @ floats
• W=F

2. Hot air balloon
• Downwards
• Temperature decrease, volume of balloon decrease
• Volume of air displaced decrease
• Buoyant force decreases
• W>F
• Upwards
• Temperature increase, volume increase
• Volume of air displaced increase
• Buoyant force increases
• W
• Constant depth
• W=F

3. Plimsoll line
• In cooler or denser water, ship floats more.
• In warmer or less dense water, ship sinks more.
• Goal: to ensure the ship is loaded within safety limit

4. Hydrometer
• In low-density liquid
• hydrometer sinks deeper