Applying Archimedes’ Principle

Previous Lesson1. Pressure

What is Pressure?? • Pressure is defined as force per unit area• P = F A

2. Pressure in liquids• P = hρg

Learning Outcomes:

At the end of this lesson, you should be able to:

• Explain Buoyant Force• Relate buoyant force to the weight

of the fluid displaced• State Archimedes’ Principle

Today’s Activities:

1. Class activity – to investigate the relationship between the buoyant force and weight of fluid displaced.

2. Group discussion on Archimedes Principle’s application.

LETS THINK ABOUT THIS SITUATION!

SITUATION 1 SITUATION 2

Lift a rock in water Lift a rock in air

Which situation is easier ?? Why??

LETS TRY THIS!!

• This is due to a force that we call as BUOYANT FORCE.

• What is actually BUOYANT FORCE??

What is Buoyant Force??

An upward force resulting from an object being wholly or partially

immersed in a fluid.

Buoyant Force is….

What is the relationship between the buoyant force and the weight of fluid displaced??

Buoyant force

Liquid displaced

ACTIVITY !!!

To investigate the relationship between the buoyant force and the weight of fluid displaced

BUOYANT FORCE

OBSERVATION AND DATAWEIGHT IN AIR

WEIGHT IN WATER

WEIGHT OF EMPTY BEAKER

WEIGHT OF BEAKER PLUS DISPLACED WATER

The story behind the principle

• king had new gold crown and suspicious that the jeweler hadn’t cheated him by adding another material.

• The king asked Archimedes to solve his problem by not changing the shape of the gold crown.

• Still concentrating on the problem,Archimedes immersed himself in the water.

• The water spilled over the sides of the tub and onto the floor.

• Arhimedes reasoned : there must be a relationship between volume and volume of water that his body displaced.

• This observation brought Archimedes back to the problem of the gold crown.

• Archimedes find gold and silver that had the same mass.

• He dropped both metal in water and observe the water that spilled out.

• Athough they had the same mass, the silver spilled out more water because the silver less dense than the gold.

• Archimedes check the crown.• He placed gold crown n pure gold

that had the same mass in water.• The crown displaced more water.• The density was less than the pure

gold.• The king had been cheated!!

ARCHIMEDES’ PRINCIPLE…

State that, when an object is wholly or partially immersed in a fluid, it experiences a buoyant force equal to the weight of fluid displaced.

ACTIVITY !!!

Applications of Archimedes Principle…

• HYDROMETER• PLIMSOL LINE• SUBMARINE

• HOT AIR BALLOON

In group, find..- The working principle- How Archimedes Principle was applied?

Shipa) The ship may sink too deeply into

water due to overloading or changes in water density when sails from one ocean to another ocean.

b) Plimsoll Line is mark on the hull of all ships to show the depths which are safe for them to navigate.

c) Normal density = BFreshwater = F or TF

Cool ocean = W

Submarine (Kapal selam)

• Submarine has ballast tank to control its position and depth below sea level.

• To float halve, water in ballast tank is driven out until the buoyant force is equal to weight of submarine.

• To fully float, water in ballast tank is driven out until the buoyant force is bigger than the weight of submarine

• To submerged, water is pumped into ballast tank until weight of submarine is bigger than buoyant force.

Hot-air Balloonsa) The weight of balloon is decrease when

its envelope is filled with gas of lower density than air (such as hydrogen or helium)

b) Total weight = weight of fabric + weight of gas in envelope

c) When buoyant force = total weight of the balloon, it remains stationary or move upward with constant velocity.

d) When buoyant force > total weight of the balloon, it accelerates upward.

HYDROMETER• Is used to compare /

determine the density of liquids.

• Lead shots is placed at the bottom to makes the hydrometer upright (tegak) in the liquid.

• In denser liquid, hydrometer will float more because volume / weight of liquid displaced is smaller than in less dense liquid.

Learning Outcomes…

1. Explain Buoyant Force

2. Relate buoyant force to the weight of the liquid displaced

3. State Archimedes Principle

The upward force resulting from an object being wholly or partially immersed in a fluid.

BUOYANT FORCE = WEIGHT OF THE LIQUID DISPLACED(for an object which immersed wholly or partially in fluid)

State that when object is wholly or partially immersed in a fluid,it experiences a buoyant force equal to the weight of the fluid displaced.

Homework!!

1. Page 100 in text bookQuestion 1 and 2

That’s all for today

Thank you for your attention!!