Published on: **Mar 4, 2016**

- 1. Teacher N TBS2011 PRESSUREDefinition : Force per unit area on the surface.Formula : F P :………………, F :…………, A :……....…. P= AUnit S.I of Pressure : ……………… or ………………….Example 1 : Which shoe will exert a greater pressure on the when it is worn by the samewomen?Answer :……. A BApplications of Pressure :(1) Tools like knives, scissors, axes and saws have sharp cutting edges. Thesurface area of contact is …………… When a force is applied on the tools, thesmall area of contact will produce a …………… pressure to cut the material.(2) Walking over deep snow is difficult and tiring because your feet sink at everysteps. Skies or snowshoes make it much easier because they stop you fromsinking in. The skies causes the pressure becomes …………….Exercise 1: A table of mass 50kg has 4 legs is placed on a floor. Each legs has across sectional area of 25cm2. Find the pressure exerting on the floor (g=10ms-2).Solution : 1
- 2. Teacher N TBS2011 PRESSURE IN LIQUIDDensity ( ρ ) is defined as: mass per unit volume. S.I Unit is kg m -3 . Oil Density ( ρ ) = mass , ρ = m volume V WaterLiquids have pressure because of their ……………... HoneyPressure in liquids acts in ……….directions..The pressure in a liquid is the product of depth (h), density ( ρ ) and gravitational acceleration(g).The above formula can be derived from the following steps: Mass of a cylinder of water, m = ρV = ……………… Weight of the cylinder of water, W = ………..= …………….. A cylinder of water A Volume h The pressure of water at the base of the cylinder of water is, V = Ah F W m g ρ Ah g Water pressure, P = = = = = ρ g h A A A AFrom the final expression , we can say that the pressure at any point in a liquid at rest is………………………… to the density of liquid and the depth.The pressure in the liquid is not dependent on the surface area and the…………. of acontainer. 2
- 3. Teacher N TBS2011Example 1 : A balloon is situated at 10 m below sea level, what is the total pressure experienceby the balloon ? [ The density of sea water is 1100 kg m-3 ] Total Pressure, P = Atmospheric pressure + Liquid pressureAtmospheric pressure at sea level : = 100,000 N m-2 + ρ g h = 100,000 + …………………….. Patm = 1.0 x105 Pa = 100,000 + …………………….. = ………………N m-2 = ……………. PaExercise 1: Given that the density of mercury is 13600kgm-3. Calculate the pressure of mercuryat a point 25 cm from the mercury surface (g =10ms-2).Solution:Applications of Pressure in Liquids.(1) Water Tank : Normally a water tank is placed at higher level so as to supply water at greaterpressure.(2) Dam : The wall of a dam is much thicker at the bottom than at the top because it mustwithstand the increased lateral pressure in depths of the water.(3) Submarine : Submarine is built with thick wall so as to withstand enormous pressure atgreater depth.(4) Hydraulic System 3