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Pressure

Pressure. Solid Incompressible Subject to shear force. Gas Compressible Not subject to shear force. Solids, Liquids, and Gases. Normal matter is made of atoms. Atoms can interact to form three types of matter. Liquid Incompressible Not subject to shear force. Density.

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Pressure

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  1. Pressure

  2. Solid Incompressible Subject to shear force Gas Compressible Not subject to shear force Solids, Liquids, and Gases • Normal matter is made of atoms. • Atoms can interact to form three types of matter. • Liquid • Incompressible • Not subject to shear force

  3. Density • Matter has mass and takes up volume. • The ratio of the mass to the volume is the density. • Incompressible materials maintain their density. Salt (solid): 2.165 x 103 kg/m3 Water (liquid): 1.000 x 103 kg/m3 Nitrogen (gas): 1.251 kg/m3

  4. Pressure • Liquids and gases are fluids. • Fluids exert a force in all directions. • Same force in all directions • The ratio of the force exerted by a fluid to the area is the pressure. • It’s a scalar, not a vector

  5. Any area in the fluid experiences equal forces from each direction. This is just the law of inertia. All forces are balanced Forces are still vectors Any arbitrary volume in the has balanced forces. Surface Force

  6. Fluids at Depth • Vertical pressures are not the same. • Pressure below is higher • Pressure above is less • Include the weight Ft Fg Fb

  7. The deepest point in the ocean is 11.3 km. Atmospheric pressure is 1.0 x 105 Pa, and water density is 1000. kg/m3. What is the pressure at that depth? The pressure increases linearly with depth. Solve for P = P0 + rgh. h is positive with depth. Substitute values: rgh = (1.00 x 103 kg/m3) (9.81 m/s2)(11.3 x 103 m) = 1.11 x 108 Pa. This is much larger than P0. P = 1.11 x 108 Pa = 1100 atm! Deep Sea Force

  8. Pascal’s Law • A change in pressure in a fluid is transmitted to all parts of the fluid equally. Equal pressures, different forces

  9. Barometer • Atmospheric pressure can be measured by balancing weight pressure against air pressure. • A device that uses this is a barometer. This barometer uses the weight of a column of liquid mercury. The meter measures the height in inches.

  10. Manometer • A manometer compares two different pressures. • Gas compared to air (tire gauge) • Liquid compared to air Gauge pressure is defined as the pressure minus atmospheric pressure. next

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