# Basic explanation: Hot air rises. Basic explanation: Buoyancy.

## Presentation on theme: "Basic explanation: Hot air rises. Basic explanation: Buoyancy."— Presentation transcript:

Basic explanation: Hot air rises.

Basic explanation: Buoyancy.

Archimedes’ Principle What 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 A B B

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 A B 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/cm 3 sinking in oil of density ρ=0.9300 g/cm 3. 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/cm 3 ) 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/cm 3. 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 ◦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/cm 3 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/cm 3 ?

It is said that iceberg floats in seawater (1.03 g/cm 3 )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/cm 3 ) and water (1.0 g/cm 3 ) as shown below? 2.00 cm