1. Physics 101: Lecture 24, Pg 1 Exam 2 : The average increased from 62 to 66 % !

2. Physics 101: Lecture 24, Pg 2 Physics 101: Lecture 24 Fluids: Pascal and Archimedes l Today’s lecture will cover Textbook Sections 11.5-11.6 è Archimedes Principle & Buoyancy è Pascal’s Principle Note: Everything we do assumes fluid is non-viscous and incompressible.

3. Physics 101: Lecture 24, Pg 3 Pascal’s Principle l Any change in pressure applied to a completely enclosed fluid is transmitted undiminished to all parts of the fluid and the enclosed walls. Example: hydraulic lift Consider two pistons with area A 1 and A 2 at the same height at different ends of an enclosed fluid. Am external Force F 1 is applied to piston 1. Consequently the fluid exerts a force on piston 2 which is related to F 1 as follows F 2 = F 1 (A 2 / A 1 )

4. Physics 101: Lecture 24, Pg 4 Archimedes Principle l An object fully or partially immersed in water experiences an upward force due to the difference in fluid pressure at different depths. This net force exerted on the object by the fluid is called the buoyant force : F B = P 2 A – P 1 A = (P 2 -P 1 ) A =  g h A Using that h A=V is the volume of the fluid and that  V=m is the mass of the fluid one finds that F B = weight of fluid displaced by the object

5. Physics 101: Lecture 24, Pg 5 Archimedes Principle cont. l When does an object float ? An object floats when the upward acting buoyant force is balanced by the downward acting weight of the object: F B = weight of object Also F B = weight of displaced water => For a floating object: W object = W displaced fluid

6. Physics 101: Lecture 24, Pg 6 Archimedes Principle (summary) l Buoyant Force (F B ) è Buoyant force = weight of fluid displaced è F B =  fluid x V displ g è W = Mg =  object V object g l If object floats…. è F B =W è Therefore  fluid g V displ. =  object g V object è Therefore V displ. /V object =  object /  fluid

7. Physics 101: Lecture 24, Pg 7 Concept Question Which weighs more: 1. A large bathtub filled to the brim with water. 2. A large bathtub filled to the brim with water with a battle-ship floating in it. 3. They will weigh the same. Tub of water Tub of water + ship Overflowed water CORRECT Weight of ship = Buoyant force = Weight of displaced water