The direction of the force producing a pressure is perpendicular to the area of interestġ0 Measuring Pressure The spring is calibrated by a known force Force Pressure is a scalar and force is a vector Has a definite volume and shape Liquid Has a definite volume but not a definite shape Gas – unconfined Has neither a definite volume nor shapeģ States of Matter, cont All of the previous definitions are somewhat artificial More generally, the time it takes a particular substance to change its shape in response to an external force determines whether the substance is treated as a solid, liquid or gasĤ Fluids A fluid is a collection of molecules that are randomly arranged and held together by weak cohesive forces and by forces exerted by the walls of a container Both liquids and gases are fluidsįluid Statics Describes fluids at rest Fluid Dynamics Describes fluids in motion The same physical principles that have applied to statics and dynamics up to this point will also apply to fluidsĦ Forces in Fluids Fluids do not sustain shearing stresses or tensile stresses The only stress that can be exerted on an object submerged in a static fluid is one that tends to compress the object from all sides The force exerted by a static fluid on an object is always perpendicular to the surfaces of the objectħ Pressure The pressure P of the fluid at the level to which the device has been submerged is the ratio of the force to the areaĨ Pressure, cont Pressure is a scalar quantityīecause it is proportional to the magnitude of the force If the pressure varies over an area, evaluate dF on a surface of area dA as dF = P dA Unit of pressure is pascal (Pa)ĩ Pressure vs. 2 States of Matter Solid Liquid Gas – unconfined

Fluid mechanics ppt