Physics 5B L Lecture 11 JJanuary 9 9 2012 Chapter 13 Fl Fluids Ch t 13 id Syllabus Course web site http scipp ucsc edu johnson physics 5b htm htt sci csc ed j hns n h sics 5b htm and eCommons The official document is online online which I will update as necessary Don t relyy too much on the ppaper p copy py i clicker registration Register using your eCommons ID CruzID not your UCSC numeric student ID For example my ID would be rjohnson since my UCSC email is rjohnson ucsc edu j 2 Laboratory laboratoryy attendance is mandatoryy for this week for registration purposes Students who do not show up p without prior arrangements will be dropped from the labs 3 Density Mass p per unit volume What is the mass of a cubic meter of water 1 gram g B 1 kilogram C 10 kilograms C D 1 metric ton 1000 kg A 4 Density of Air What is the approximate mass of a cubic meter of air 1 gram B 1 kilogram g C 10 kilograms D 1 metric ton 1000 kg D A Dry air at STP has a density of about 1 3 1 3 kg m3 5 Pressure Molecules bouncing off of a surface apply an impulsive force to the surface perpendicular to the surface http phet colorado edu simulations sims php sim Gas Properties 6 Pressure acts in all directions on any surface in the fluid always applying force perpendicular to the surface Important pressure is a scalar quantity while h l fforce is a vector 1 atmosphere pressure sea level average is 100 000 Pa 1 bar 7 With atmospheric pressure 100 100 000 N m2 the side of a can like this must have a force on it of nearly 10 10 000 N 11 ton ton Why doesn t it get instantly crushed flat 8 We can remove most of the air by boiling the water in the Now why bottom of the can can The steam pushes the air out out Now doesn t the can get instantly crushed 9 Magdeburg Hemispheres Otto von Guericke in 1650 10 Magdeburg Hemispheres 11