1. Pressure

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

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 10 3 kg/m 3 Water (liquid): 1.000 x 10 3 kg/m 3 Nitrogen (gas): 1.251 kg/m 3

4. Pressure  Liquids and gases are fluids.  Fluids exert a force in all directions. Same force in all directionsSame 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 vectorIt’s a scalar, not a vector

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

6. Fluids at Depth  Vertical pressures are not the same. Pressure below is higher Pressure above is less Include the weight FgFg FbFb FtFt

7. Deep Sea Force  The deepest point in the ocean is 11.3 km. Atmospheric pressure is 1.0 x 10 5 Pa, and water density is 1000. kg/m 3.  What is the pressure at that depth?  The pressure increases linearly with depth.  Solve for P = P 0 +  gh.  h is positive with depth.  Substitute values:   gh = (1.00 x 10 3 kg/m 3 ) (9.81 m/s 2 )(11.3 x 10 3 m) = 1.11 x 10 8 Pa.  This is much larger than P 0.  P = 1.11 x 10 8 Pa = 1100 atm!

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)Gas compared to air (tire gauge) Liquid compared to airLiquid compared to air Gauge pressure is defined as the pressure minus atmospheric pressure. next