Archimedes’ and Pascal’s

Principles

ARCHIMEDES’ PRINCIPLE

ARCHIMEDES’ PRINCIPLE

Archimedes' principle states that the apparent loss in weight of a body that is totally or partially immersed in a liquid is equal to the weight of the liquid displaced.

Archimedes supposedly formulated this principle after stepping into a bath and watching it overflow. According to legend, he became so excited that he ran out into the street naked shouting "Eureka! Eureka" ("I've found it! I've found it!")

ARCHIMEDES PRINCIPLE

Volume: space taken up by an objectThe volume of fluid displaced (pushed out of the way) by an object equals the volume of object. Buoyant Force – upward force exerted by fluidThe buoyant force on an object equals the weight of the fluid displaced by the object.http://www.youtube.com/watch?v=QvZR7eUvLZA&safety_mode=true&persist_safety_mode=1

http://www.youtube.com/watch?v=vJ36urazDu4

http://www.youtube.com/watch?v=eQsmq3Hu9HA

DENSITY

Density: ratio of mass to volume

If two objects have same volume, which one has greater density: one with more mass OR one with less mass?

If two objects have same mass, which one has greater density: one with more volume OR one with less volume?

ARCHIMEDES PRINCIPLE

The buoyant force on an object equals the weight of the fluid displaced by the object. Buoyancy is the upward force exerted by fluids.

•http://www.youtube.com/watch?v=vJ36urazDu4

•http://www.youtube.com/watch?v=eQsmq3Hu9HA

FLOAT OR SINK OR???

If the buoyant force > weight, object will float at surface of fluid.

If the buoyant force = weight, object remains suspended in fluid.

If the buoyant force < weight, object sinks.

WHERE IS THE BUOYANT FORCE GREATER?

Freshwater or Saltwater?

Air or water?

Oil or water?Reading in the Great Salt Lake, Utahhttp://www.youtube.com/watch?v=TDEzBWjQpQI&safety_mode=true&persist_safety_mode=1http://www.youtube.com/watch?v=wZrWlzHFC4k&feature=fvwp&NR=1&safety_mode=true&persist_safety_mode=1

ARCHIMEDES’ PRINCIPLE

The weight of the

displaced fluid is

directly proportional

to the volume of the

displaced fluid.

HOW CAN SHIPS MADE OF STEEL FLOAT?

A piece of solid steel sinks in water, but the shape of a ship’s hull allows it to displace a large volume of water.

This creates a large buoyant force, which counteracts the ships huge weight.

The effective density of the ship is less than water.

BALLAST WATER - SUBMARINES

APPLICATIONS OF ARCHIMEDES’ PRINCIPLE

Submarines

A submarine has a large ballast tank, which is used

to control its position and depth from  the surface

of the sea.

A submarine submerges by letting water into the ballast

tank so that its weight becomes greater than the buoyant

force (and vice versa). It floats by reducing water in the

ballast tank - thus its weight is less than the buoyant force.

BALLAST WATER - SHIPS

HOT AIR BALLOONS

A hot air balloon rises and floats due to the buoyant force (when the surrounding air is greater than the balloon’s weight). It descends when the balloon’s weight is more than the buoyant force. It becomes stationary when the weight equals the buoyant force.

The weight of the hot-air balloon can be controlled by varying the quantity of hot air in the balloon.

SWIM BLADDERS IN FISH

WHERE IS THE BUOYANT FORCE GREATER?

Freshwater or saltwater?

Air or water?

Oil or water?

HYDROMETERA hydrometer is an instrument to

measure the relative density of liquids.

It consists of a tube with a bulb at one

end. Lead shots are placed in the bulb

to weigh it down and enable the

hydrometer to float vertically in the liquid.

In a liquid of lesser density, a greater volume of liquid

must be displaced for the buoyant force to equal to the

weight of the hydrometer so it sinks lower.

A hydrometer’s small floats higher in a liquid of higher density.

PASCAL’S PRINCIPLE

PASCAL’S PRINCIPLE

A CHANGE IN PRESSURE at any point in an enclosed fluid is transmitted EQUALLY and

unchanged in all directions THROUGHOUT the fluid and to the walls of the container

HYDRAULICSWhen a small force or load is placed

on the small piston (F1), it acts

through the liquid to the large piston

to produce a

very large force

on F2 that causes the

load to rise a

Shorter distance.

PASCAL’S PRINCIPLE DIAGRAM

Left cylinder Right cylinderCross section = 1 in2 Cross section = 10 in2

Force = 1 pound Force = 10 poundPiston lowered = 10” Piston raised: 1”

The 1 pound load on the 1 square inch area causes an increase in pressure on the fluid in the system.As a result, the larger piston lifts upa 10 pound weight. The larger the cross-section area of the second piston, the larger the mechanical advantage, and the more weight it can lift.

APPLYING PASCAL’S PRINCIPLE

A hydraulic jack operates on Pascal’s PrincipleCan you see why it’s much easier to use a hydraulic jack to lift a car than by hand?http://www.edumedia-sciences.com/en/a260-hydraulic-lift

HYDRAULIC PRESS

The hydraulic press is applied in our daily life:

Hydraulic car jack. Hydraulic brakes.