Pressure and Buoyant Force Fluids Pressure Pressure is the amount of force exerted on a given area of surface. Fluids exert pressure evenly in all directions. Pressure To calculate pressure you divide force over area

~Common Units for Force

-Newtons (N)

-Weight (lb)

~Common Units for Area

-Square Inches (in2)

-Square Meters (m2)

~Common Unit for Pressure

-Pascal (One pascal (1 Pa) isA the force of one newton exerted over an area of one square meter (1 N/m2). The newton is the SI unit of force) Buoyant Force ~All fluids exert an upward buoyant force on matter.

~Buoyant force results from the fact that pressure increases with depth. The forces pushing up on an object in a fluid are greater than the forces pushing it down. Thus, there is a net upward force: the buoyant force. Calculating Pressure How much pressure is exerted on a science lab desk which measures 24 inches deep and 30 inches long by the air column above it pushing down with a weight of 10,584 lb. Where have you heard the word Pressure before? Pressure (P) = Force (F)

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Area (A) Calculate the pressure exerted on the heel of a boy’s foot if the boy weighs 80 N and he lands on one heel which has an area of 16 cm2. Buoyancy Archimedes’ Principle ~ is used to find Buoyant Force

~States that:

-The buoyant force on an object in a fluid is an upward force equal to the weight of the fluid that the object displaces. Buoyancy and Density Buoyancy and Density ~Steel is almost eight times denser than water but huge steel

ships cruise the oceans with ease.

-The shape of the ship allows the ship to float, the hollow shape decreases the ship’s density. For example, imagine that you put a brick in a container of water, as depicted on the right. The total volume of water that collects in the smaller container is the displaced volume of water from the larger container. The weight of the displaced fluid is equal to the buoyant force acting on the brick. You can determine whether an object will float or sink by comparing the buoyant force on the object with the object’s weight, as the Figure above shows. Note that the seagull is only partly underwater. The seagull’s feet, legs, and stomach displace a weight of water that is equal to the seagull’s total weight. So, the seagull is buoyed up and floats on the water’s surface. ~An object will float or sink based on its density

~Examples:

-the density of a brick is about 2 g/cm3, and the density of water is 1.00 g/cm3. The brick will sink in water because it is denser than the water.

-Helium has about one-seventh the density of air. A given volume of helium in a balloon displaces a volume of air that is much heavier than helium, so the balloon floats.

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# Fluids

Pressure, Archimedes’ Principle, and Buoyancy

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