Unit 6 Pressure PDF

Unit 6 : Pressure Contents: States of Matter Basic concepts of Pressure Example Pressure and Fluids Absolute pressure Questions Dr. Khaled Ilaiwi 1 states of matter Matter is normally classified as being in one of...

Unit 6 : Pressure Contents: States of Matter Basic concepts of Pressure Example Pressure and Fluids Absolute pressure Questions Dr. Khaled Ilaiwi 1 states of matter Matter is normally classified as being in one of three states: solid, liquid, or gas. solid has a definite volume and shape liquid has a definite volume but no definite shape gas has neither a definite volume nor a definite shape Dr. Khaled Ilaiwi 2 Pressure and states of matter Water in the three states of matter Pressure types due to liquid Random motion of gas molecules and pressure on container walls Basic concepts of Pressure or Pressure gauge Pressure and area Pressure and area: Example The mattress of a water bed is 2 m long by 2 m wide and 30 cm deep. (A) Find the weight of the water in the mattress. (B) Find the pressure exerted by the water bed on the floor when the bed rests in its normal position. (A) (B) Pressure and Fluid A fluid is a collection of molecules that are randomly arranged and held together by weak cohesive forces. Both liquids and gases are fluids. When an object is submerged into a non-moving (static) fluid → F exerted on the object perpendicular to the surfaces of the object All points at the same depth must be at the same pressure. Pressure at the same elevation is the same regardless the shape of the container Fluid Pressure Hydrostatic pressure: pressure of static fluid at a given point into the fluid due to gravity force on fluid at that point. Fluid exert equal pressure in all directions at the same depth Hydrostatic pressure increases is proportional to the depth measured from the surface of the fluid because of the increasing weight of fluid exerting downward force from above Fluid Pressure Static Fluid pressure is given by: Where ρ = m/V is the fluid density, V=Ah is the fluid volume, h is the height of fluid above measured point, and g = 10 m/s2 is the gravity acceleration This pressure is called Static fluid pressure or Hydrostatic pressure or Gauge pressure  Absolute pressure Absolute Pressure 0.5 atm Absolute pressure or total pressure is the pressure 1 atm relative to a full vacuum (zero pressure) 2 atm If a fluid in a container that is open to atmosphere, then the absolute pressure of the fluid is the sum of 3 atm atmospheric pressure gauge pressure: Where P0 is the atmospheric pressure (Pa) , and ρgh is the gauge (fluid) pressure Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere Fluid Pressure: Example Find the force exerted on your eardrum due to the water when you are swimming at the bottom of a pool that is 5 m deep. Assume eardrum area is about 0.53 cm2. Normally eardrum is at atmospheric pressure P0. The change in pressure on ear drum Pwater = ρgh F = PA = 4.9×104 (0.53×10-4) = 2.6 N (This may damage the ear drum)  Questions : Q1) A diver is 10 meters underwater in a lake. If the density of water is 1000 kg/m3 1000 and g=9.8 m/s2 , calculate the pressure exerted by the water at that depth. Ignore atmospheric pressure. Q2) Two points in a liquid are at depths of 5 m and 15 m. If the fluid density is 1200 kg/m3 , calculate the difference in pressure between the two points. Q3) A tank contains water, and the pressure at the bottom is 29,400 Pa. If g=9.8 m/s2 and the density of water is 1000 kg/m31000kg/m3, find the depth of the water. Dr. Khaled Ilaiwi 12