F08_lec16

# F08_lec16 - P1112 Lecture 16 Oct 3rd 2008 Last unit about...

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P1112 Lecture 16 Oct 3rd, 2008

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Last unit about forces: Forces in Fluids Pressure and Buoyancy • Pressure in incompressible ﬂuids • Archimedes Principle
Pressure Object in ﬂuid: atoms bounce off Each surface feels a force proportional to its area Units: Pascals = Newtons/meters 2 Pressure acts in all directions

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area A Normal atmospheric pressure is: p atm = 1.0 ! 10 5 N/m 2 = 14.7 pounds/inch 2 . The total force acting down on a 1 m ! 2 m table top due to this air pressure equals the combined weight of about how many people? (1) < 1 (2) 3 (3) 30 (4) 300 (5) 3000
Fixed sealed volume • Increase density – More particles bouncing • More pressure • Increase temperature – Increase average speed of particles • Increase momentum transfer in bounce • Increase pressure

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Pressure varies with depth Break ﬂuid into small bits A B C δ y Height y
Pressure varies with depth A B C δ y Take δ y to 0

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Incompressible ﬂuid Water: density roughly constant -- incompressible Air: density varies with height -- compressible Density constant: Corollary: Pascal’s principle If pressure is applied to an enclosed ﬂuid the pressure at any depth increases by exactly the same amount
Hydraulic Lift Small force here

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## This note was uploaded on 10/04/2008 for the course PHYS 1112 taught by Professor Leclair,a during the Fall '07 term at Cornell.

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F08_lec16 - P1112 Lecture 16 Oct 3rd 2008 Last unit about...

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