2. Quick Quiz
A diver is submerged below the surface of the ocean.
If the diver experiences a total pressure of 202
kPa, how deep is the diver underwater?
If the diver has a face mask that is circular, with a
diameter of 15 cm, what is the force that the water
exerts on the glass?
3. What If?
Check out the apparatus you see before you. There is a
spring scale, reading the weight of the object and a
beaker of water. What will the scale read when the
object is submerged?
4. Archimedes first thought of
this…
ARCHIMEDES was asked to check the suspected
presence of silver alloy in the king’s gold crown. The
solution which occurred when he stepped into his
bath and caused it to overflow was to put a weight of
gold equal to the crown, and known to be pure, into
a bowl which was filled with water to the brim. Then
the gold would be removed and the king’s crown put
in, in its place. An alloy of lighter silver would
increase the bulk of the crown and cause the bowl to
overflow. So delighted was Archimedes with his
solution that he leaped from his bath and ran
through the streets of Syracuse crying “Eureka!”
Presumably you won’t be in your bath when you read
NBC’s new facts, but we would not be surprised to
hear you, too, shout “Eureka!” (This illustration and
text are from a magazine advertisement for
NBC, probably dating from the 1940’s. It was found
among the files of the Print and Picture Department
of the Free Library of Philadelphia. The word
“eureka!” is coming out of Archimedes’ mouth.)
5. Buoyant Force
Buyoant force on any object is equal to the weight of
the fluid displaced by the object (in whole or in part).
How do we calculate that?
Density = m/v so mass = (density*volume)
Fb = density of fluid * volume of water displaced * g
3 cases and free-body diagrams for eah
6. Example:
A raft is constructed of wood having a density of 300
kg/m3. Its surface area is 6.0 m3. When the raft is placed
in fresh water of density 1000 kg/m3, to what depth
does the raft sink in the water?
How many of your friends (average mass = 65 kg could
join you on the raft – also with mass of 65 kg) before it
sunk?
