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Lecture16_Pushkar

# Lecture16_Pushkar - PHYSICS 220 Lecture 16 Fluids Lecture...

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Lecture 16 Purdue University, Physics 220 1 Lecture 16 Fluids PHYSICS 220

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Lecture 16 Purdue University, Physics 220 2 States of Matter Solid Hold Volume Hold Shape Liquid Hold Volume Adapt Shape Gas Adapt Volume Adapt Shape Fluids
Lecture 16 Purdue University, Physics 220 3 Pressure Pressure = F normal / A Scalar Units: Pascal (Pa) = N/m 2 Atmosphere: 1 atm = 101.3 kPa 1 atm ~ 10 N/cm 2 ~ 15 lb/in 2 Force due to molecules of fluid colliding with container. Change in Impulse = p

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Lecture 16 Purdue University, Physics 220 4 y average vertical force = f y = p y t = mv y t Illustration
Lecture 16 Purdue University, Physics 220 5 Atmospheric Pressure Basically weight of atmosphere! Air molecules are colliding with you right now! Pressure = 1 × 10 5 N/m 2 = 14.7 lbs/in 2 Example 1: Plate r = 2.4 in A = π r 2 = 18.1 in 2 F = P A = (14.7 lbs/in 2 )(18.1 in 2 ) = 266 lbs Example 2: Sphere r = 0.1 m A = 4 π r 2 = 0.125 m 2 F = 12,000 N (over 2,500 lbs)!

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Lecture 16 Purdue University, Physics 220 6 Atmospheric Pressure You buy a bag of potato chips in Lafayette and forget them (un-opened) under the seat of your car. You drive out to Denver Colorado to visit a friend for Thanksgiving, and when you get there you discover the lost bag of chips. The odd thing you notice right away is that the bag seems to have inflated like a balloon (i.e. it seems much more round and bouncy than when you bought it). How can you explain this ? Due to the change in height, the air is much thinner in Denver. Thus, there is less pressure on the outside of the bag of chips in Denver, so the bag seems to inflate because the air pressure on the inside is greater than on the outside.
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