Floating and Sinking
n How is it possible that huge ships made of _____________________ can float easily in water?
n Yet in a few hours the same ship can become a sunken __________________ like the Titanic.
n Why does most of an iceberg lie hidden _______________________ the surface of the water?
n To answer these questions, you need to find out what makes an object ______________ and what make an object ______________________.
Comparing Densities
n One reason objects float or sink is their ________________________.
n An object that is _________________________________________ than the fluid in which it is immersed ______________________.
n An object that is _______________________________________ than the fluid in which it is immersed ____________________________ to the surface.
n If the density of an object is ____________________ to the density of the fluid in which it is immersed, the object neither rises nor sinks in the fluid; it ______________________________
____________________________________________.
Floating and Sinking
n Now you know why __________________ sinks: it is several times ________________ than water.
n __________________________, which is less dense than water, _____________________.
n Is an ice cube more or less dense than water?
Iceberg straight ahead!
n An ice cube _________________ in water because the density of ice is ___________________ than the density of water.
n But it’s just a ________________________________!
n So most of a floating ice cube is __________________________________________________.
n Since an iceberg is really a very large ice cube, the part that you see above water is only a _________________________________________________of the entire iceberg.
n This is one reason why icebergs are so dangerous to ships.
Buoyant Force
n If you have ever picked up an object under water, you know that it seems _________________ in water than in air.
n Water exerts a force called ____________________________ that acts on a submerged object.
n Buoyant force acts in the __________________________ direction, against the force of gravity, so it makes an object feel ______________________________.
Weight vs. Buoyant Force
n There is always a _______________________________ force on a submerged object.
n That force is the _______________________ of the object.
n If the weight of the object is __________________________ than the buoyant force, the object will ___________________.
n If the weight of the object is _________________ than the buoyant force, the object will begin to ________________
n What can you infer about the weight and buoyant force from the last picture?
Archimedes’ Principle
n You know that Archimedes discovered that a submerged object displaces, ________________
_________________________________________, a volume of fluid equal to its own volume.
n Using this idea, Archimedes came up with a principle that relates _______________________
___________________________a submerged object ______________________to the __________________________________________________on the object.
n It states that the buoyant force on an object is _____________________________ the weight of the fluid displaced by the object.
n Therefore, the ________________________________ an object ________________________, the ________________________________________________________________ it will have.
n The more ______________________________ an object occupies, the more water is displaces.
n This is why it is easier to float in water when you are __________________________________ on your back – you take up __________________ surface area, displacing ____________ water, therefore creating a ________________________ buoyant force.
Floating by changing mass
n Changing the density of an object can make it _______________________________ in a given fluid.
n Even though you cannot change the density of an individual substance, you can change the overall density of things that are made of ____________________________________.
n Submarines can change their overall _____________________, and therefore their density to allow them to float and sink.
n They do this by filling or releasing water from their ________________________________.
n When water is pumped _______________ of its flotation tanks, the overall mass of the submarine __________________________.
n Since the volume remains the same, its density __________________________________ when its mass ______________________________.
n So the submarine will _____________________ to the surface.
n What do you think a submarine does in order to sink?
n To dive, the submarine _______________________________________________.
n In this way, it _______________________________________ (and thus its density) and sinks!
n Most ships are also designed to alter their overall density.
n The _________________ (bottom part) of a ship contains a large volume of _____________.
n This air reduces the ship’s overall __________________________, and therefore its density, and helps it to float.
Floating by changing volume
n Another way of changing density is to change __________________.
n If the mass is kept the same, ________________________________ the volume of a substance, will ________________________________ its density.
n Increasing the ___________________________________ of a substance, will also increase its _________________________________________.
n This is because the ___________________________________ of water displaced, the ___________________________________________________ (Archimedes Principle).
n The ____________________________ of a ship causes it to displace a greater volume of water than a solid piece of steel of the same mass because it has a greater surface area.
n The ______________________water it displaces, the easier it will float!
n A ship stays afloat as long as the buoyant force is _________________________ its weight.