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

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

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

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

Pg 427 Buoyancy Buoyancy: the ability to float

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

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

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

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

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

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

Chapter 11 Section 2 Homework Pg 429

1A. What is density?

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

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.

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

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

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?