# Physical Science Chapter 3

Physical Science Chapter 3 Forces in Fluids Pressure = Force / Area Pressure: a force pushing on a surface Pressure = Force / area Unit of measure for Pressure is the Pascal: 1Pa = 1N/m2 Remember 1 N = 1kg m/ sec2

Fluid Pressure Fluid is a substance that can flow easily. Scientifically liquids & gases are considered fluids In fluids, molecules are constantly moving in all directions As a molecule moves and collides w/ a surface, it exerts a force on that surface All of the forces exerted by the individual molecules are added together to make up the pressure exerted by the Pascal's Vase fluid.

demonstrating that depth, not Pressure = Force / Area shape, determines fluid pressure... Air Pressure Air pressure is the result of the weight of a column of air pushing down on an area.

14.7 lbs/inch2 ( 10.13 N/cm2) 1013.25 millibars 1013.25 hPa (hecto Pascals) 29.92 inches of Hg Air exerts a balanced force when fluid is NOT moving: the pressure pushing down on your

hand is balanced by the pressure pushing up on your hand 1 in x 1 in square column of air weighs 14.7 lbs at sea level Variations in Fluid Pressure

Elevation the distance above sea level. As altitude increases Air pressure decreases As air pressure decreases, so does density. As water depth increases water pressure increases Water 800x more dense than air, so pressure

increases dramatically w/ depth every 33 ft in depth adds 1 atmosphere of pressure Pascals Principle When force is applied to a CONFINED FLUID, an increase in pressure is transmitted equally to ALL

parts of the fluid. Archimedes Principle The buoyant force on an object is equal to the weight of the fluid displaced by the object. The buoyant force is opposite (pushes up) to the force of gravity (pulls down) Bernoullis Principle The pressure exerted by a moving stream of a fluid is less than the pressure of the surrounding fluid.

The faster the fluid moves, the less pressure it exerts on the surface of the object No more lets stop time to watch American Idol !! TTFN

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