1. Section 2 – pg 424 Floating and Sinking
Chapter 11
Section 2 – pg 424
Floating and Sinking

2. Density Density: how compressed something is Pg 425
Density = Mass/Volume
This is more dense b/c there is more mass in the same area

3. Comparing Densities of Substances
Each substance has its own density
By comparing densities, you can predict whether an object will float or sink in a fluid
Less dense objects/ fluids float on top of more dense fluids
Pg 425

4. Pg 426
Changing Density
You can make an object sink or float in a fluid by changing its density

5. Pg 427
Buoyancy
Buoyancy: the ability to float

6. Gravity and the Buoyant Force
Pg 427
Gravity and the Buoyant Force
Buoyant Force: water and other fluids exert an upward force on submerged objects
The upwards pressure on the bottom of a submerged object is greater than the downward pressure on top due to the fact that pressure increases with depth
If an object’s weight is greater than the buoyant force the object sinks

7. Archimedes’ Principle
Pg 428
Archimedes’ Principle
All objects take up space
A submerged object displaces, or takes the place of, a volume of fluid equal to its own weight

8. Pg 428
Archimedes’ Principle states that the buoyant force acting on a submerged object is equal to the weight of the volume of fluid displaced by the object
Discovered by Archimedes: a Greek mathematician
If something displaces 50 liters of water then its buoyant force is equal to the weight of that water, which is 500N

9. Pg 428
Submarines
The size of the submarine is constant so the buoyant force acting on it would be constant
Changing the water level in the floatation tanks changes the weight of the submarine
If the weight of the submarine is greater than the buoyant force then the sub sinks
If the weight of the submarine
is less than the buoyant force
then the sub rises

10. Balloons Remember: air is a fluid
Pg 428
Balloons
Remember: air is a fluid
When air is in a balloon it is under pressure making it more dense than the air outside the balloon
This is why balloons filled with just air sink to the ground
Balloons filled with helium float because helium is much less dense than air
Air
Helium

11. Ships Pg 429 A large object displaces more fluid than a small object
A greater buoyant force acts on the larger object even if the large object has the same weight as the small object
Since a ship displaces more water than a block of steel, a greater buoyant force acts on the ship

12. Chapter 11 Section 2 Homework Pg 429

13. 1A. What is density?

14. 1B. How can you use the density of an object to predict whether it will float or sink in water?

15. 1C. Some canoes have compartments on either end of that are hollow and watertight. These canoes won’t sink, even when they are capsize. Explain why.

16. 2A. How does the buoyant force affect a submerged object?

17. 2B. How does Archimedes’ principle relate the buoyant force acting on an object to the fluid displaced by the object?

18. 2C. An object that weighs 340N floats on a lake
2C. An object that weighs 340N floats on a lake. What is the weight of the displaced water? What is the buoyant force?