Basic explanation: Hot air rises.

Basic explanation: Buoyancy.

Basic explanation: Buoyancy.

Archimedes’ PrincipleWhat makes it float or sink?

Prerequisites

Hydrostatic pressure varies with depth.There is greater pressure with greater

depth.

Archimedes’ Principle on Flotation

“Any floating object displaces its own weight of fluid.”

Archimedes’ Principle on Flotation

“Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.”

Which experiences greater buoyant force?

For a floating object (immersed or partially immersed):◦The buoyant force is equal to the weight of the

object.◦The buoyant force is equal to the weight of the

displaced fluid.

For a sinking or sunken object◦The buoyant force is equal to the weight of the

displaced fluid.◦The buoyant force is not equal to the weight of

the object.

Check up Quiz

A

B

Which object experiences greater magnitude of buoyant force; A or B. Why?

Which will float? Sink?

What is wrong in this picture?

Basic explanation: Hot air rises.- The buoyant force on it is greater than its weight.- The air inside has less density than the

surrounding air.

Basic explanation: Buoyancy.- The buoyant force on it is equal to its total weight.- This boat displaces a volume of fresh water equal

to its weight plus its entire load.

Basic explanation: Buoyancy.

Which experiences greater buoyant force?

oil water

A

B

A and B are of different materials but are of equal volumes

Practice

Find the acceleration of a 15.00 kg steel with density ρ=7.800 g/cm3 sinking in oil of density ρ=0.9300 g/cm3. Assume that the object starts from rest already immersed in the fluid.

Practice

It is said that iceberg floats in seawater (density is 1.03 g/cm3) with ¾ of its volume underwater. What should then be the density of this iceberg?

Practice

A cubical box 1.000 m on a side is made of steel with density ρ=7.800 g/cm3. If each face of the box is 0.01000 m thick of this steel, and one face is left open, what would be its weight?

Practice

A cubical box 1.000 m on a side is made of steel with density ρ=7.800 g/cm3. If each face of the box is 0.01000 m thick of this steel, and one face is left open, what would be its weight? ◦Will it float in water?◦If yes, until what part is submerged?

◦How many 100.0N objects can be loaded on this box before it sinks?

A slab of wood (3.00m, 1.00m, 5.00cm) of density 0.90 g/cm3 floats in water. What volume is submerged? How far from the surface is the bottom portion of the wood? What maximum weight can be loaded on this slab before it sinks?

A certain material floats in freshwater lake such that 4/5 of its volume is submerged.◦What must be the density of this object?◦Will it float in oil of density 0.75 g/cm3?

It is said that iceberg floats in seawater (1.03 g/cm3)with ¾ of its volume underwater.

What if a slab of this ice floats in freshwater lake. What minimum volume must the slab have for a 58kg woman to be able to stand on it without getting her feet wet?

What is the buoyant force on the cubic block (5.00 cm on each side) suspended in the interface of oil (0.80 g/cm3) and water (1.0 g/cm3) as shown below?

2.00 cm