Chapter 11 section 2
Floating and Sinking
Density
•
Density=mass
volume
Calculating Density
1. A sample of liquid has a mass of 24g and
a volume of 16mL. What is its density?
2. A piece of metal has a mass of 43.5g
and a volume of 15cm3. What is its
density?
• Comparing Densities of substances, to
compare the densities of different
substances, you can place them in the
same container, the densest will sink at
the bottom and the least dense will be on
the top
• Changing densities Since
Density=mass/volume changing the mass
and/or the volume will change the density
of the substance
Buoyancy
• Buoyancy is the ability of objects to float.
• The buoyant force is an upward force that fluids
exert on all matter. Buoyant force acts in the
direction opposite to the force of gravity, so it
makes an object feel lighter.
• Fluid exert pressure on all directions of
submerged object.
• If the weight of submerged object is greater than
buoyant force the object will sink, If the weight of
submerged object is equal to buoyant force, the
object will not sink. (Remember we also use
density to explain why objects sink or float).
Archimedes’ Principle
• 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.
• Submarines sink when its weight is greater than
the buoyant force. It rises when its weight is
less than the buoyant force.
• Ships; a solid block of steel sinks in water. A
steel ship with the same weight floats on the
surface since the ship displaces more water than
block of steel, a greater buoyant force acts on
the ship.