PRESSURE
Basic Competency • To describe pressure on solids, liquid and gases and also its application in daily life
Science word • Tekanan • Gaya • Luas • Zat alir • Hukum archimedes • Mengapung • Melayang • Tenggelam • Pressure • Force • Area • Fluids • Archimedes principle • Floating • Flying • Sinking
Diagram concept
After this you are able to : • Describe relation between pressure and area • Describe relation between pressure and force • Write down formula of pressure
Pressure is defined as force acting on unit area If pressure (p), force (F), and area (A), we can write the formula below Pressure in solid
The SI Unit of pressure is N/m2 or Pascal (Pa) The another unit such as Cm Hg, atmosfera (atm), Bar, dyne/cm2 Pressure in solid
Self assessment 17.1 page 103 (science book) • Mandiri hal 49 no. 1,2,8,9,12,13 • Mandiri hal 62 no 5 essay
Fluids • How can a fluid produce pressure? • Pressure in fluid is produced by collisions between particles and the container.
After this you are able to • Describe the quantities that have effect to pressure in liquid • Describe the characteristics of liquid pressure • Write down formula of hydrostatics pressure
The characteristics of liquid pressure • Pressure in liquid increase with depth • Pressure at one depth equally in all direction • Pressure depend on the density of liquid.
Formula of liquid pressure • For the information above, pressure of liquid just depend on 2 variable : • Depth (h), that have relation pressure ~ depth • Density () that have relations pressure ~ density
Formula of liquid pressure • We can write formula : p ~ .h or p = .g.h which pressure (p), depth (h), density ( ), and gravitation (g)
example • A body floats in water at a depth of 20cm. If the density of water is 1,000 kg/m3 and the acceleration due to gravity is 10 m/s2, then what is the hydrostatics pressure at the place where object floats?
Connected Vessels • Vessels filled with the same fluid have the same height levels • Vessels filled with two different kinds of fluid have different height level
Pascal’s principle • After this the student is able to • state Pascal’s Principle • applied Pascal’s Principle in daily life
Pascal’s principle • Pressure applied to an enclosed liquid is transmitted to every part of liquid, whatever the shape of liquid.
Aplication pascal’s principle • Pascal’s principle is applied in the operation of machines that use fluids to multiply force as in hydraulic lift
Hydraulic system • In a hydraulic system fluid is confined in two connecting chambers. • Each chambers has a piston that is free to move.
Example • A 50 newton force is exerted on the small piston a hydraulic system. The cross-sectional area of small piston is 0,05 m2. What is the magnitude of the weight that can be lifted by the large piston, which has a surface area of 0,2 m2?
Archimedes’ principle “an object partially or fully immersed into a fluid will undergo an bouyant force equals to the weight of the fluid displaced by the object”
Mathematically, Archimedes’ principles can be written as: Fa = ρ . Vf . g Fa = bouyant force (N) ρ = density of fluid (kg/m3) Vf = volume of a fluid that is displaced(m3) g = the earth gravitational acceleration
Example • An object which density is 1,500 kg/m3, volume is 8,000 m3 is immersed entirely into water. If ρwater = 1,000 kg/m3 what is : • Fa…..? • W in water …..?
Boyle’s Law • Robert Boyle concluded that “ the multiplication between pressure and volume of gas in an enclosed space is constant” • P .V = constant or • P1 .V1 = P2 .V2
Height place and Air Pressure • Every increase of 10 m from the sea level, the air pressure decrease 1mmHg. • h = the height of place from the sea level(m) • x = the pressure of place from the sea level(cmHg)
Example • The atmospheric pressure in of a mountain is 49 cmHg. It’s height is….. Above sea level • The height of town is 600 m above sea level. The atmospheric pressure in this town is……
