1. Pressure and Pascal's principle
1.1. Density
1.1.1. Density is the amount of matter per unit volume, the amount of atoms or molecules in a definite space.
1.1.2. p= m/v
1.1.2.1. p: density
1.1.2.2. m: mass
1.1.2.3. v: volume
1.2. Pressure
1.2.1. Pressure is the force applied on a surface.
1.2.2. Fluids exert pressure on objects immersed in them, a fluid also applies pressure on the walls of a container.
1.2.3. P= F/A
1.2.3.1. P: pressure
1.2.3.2. F: force
1.2.3.3. A: area
1.2.4. The SI unit of pressure is Pascal (Pa)
1.2.4.1. 1Pascal= 1Pa = 1 N/m2
1.3. Pressure and height
1.3.1. The amount of pressure an incompressible fluid exerts on a body also depends on its density and depth.
1.3.2. Pressure in terms of density and depth
1.3.2.1. P= pgh
1.3.2.1.1. p: pressure
1.3.2.1.2. g: gravity (9.81 m/s2)
1.3.2.1.3. h: height
1.3.3. Specific weight (D) or weight per unit volume of the fluid
1.3.3.1. D= pg
1.3.4. Pressure formula in terms of specific weight
1.3.4.1. P= Dh
1.4. Atmospheric pressure
1.4.1. The air mass of the atmosphere applies pressure that changes with depth. It changes with the altitude, time and weather conditions.
1.4.2. 1atm = 1.1013x10^5Pa
1.5. Pascal’s Principle
1.5.1. "Pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid, as well as to the walls of the container”
1.5.2. P= F1/A1 = F2/A2
1.5.2.1. F1: Force applied on the smaller piston
1.5.2.2. A1: Area of the smaller piston
1.5.2.3. F2: Force applied by the fluid on the second piston
1.5.2.4. A2: Area of the second piston
2. Flotation and Archimedes principle
2.1. When a body immersed in a fluid is less dense than the fluid, it will float.
2.2. Flotation is caused by an upward force called buoyant force.
2.3. “The buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object.”
2.4. B = mg = pVg
2.4.1. B: flotation force
2.4.2. m: mass of the displaced fluid
2.4.3. g: gravity (9.81 m/s2)
2.4.4. p: fluid density
3. Superficial tension and capillarity
3.1. Surface tension is when a liquid’s surface acts as a membrane in tension.
3.2. It is caused because all the molecules of a liquid attract each other in all directions. However, the molecules on the surface attract just sideways and downward, this makes the attraction force to be bigger on the surface
3.3. This phenomenon is responsible for the formation of droplets on the leaves of a plant.
3.4. The superficial tension makes hard for water to pass through small cracks or very tight conduits.
3.5. Capillarity is the fluid’s capacity to go up through a capillary tube (of a very small diameter). Thanks to the surface tension.
3.6. On a liquid, if its molecules have more adhesion than cohesion, the liquid adheres to the container walls.
3.7. But if cohesion is greater, it will originate a capillarity decrease.
3.8. “Ascents or descents of liquids by capillary tubes, are inversely proportional to the radio of the tubes”
3.9. h= 2σ/prg
3.9.1. h= height reached by the liquid (m)
3.9.2. σ= surface tension of the liquid in contact with air (N/m)
3.9.3. ρ= density of the liquid (kg/m3)
3.9.4. r= radius of the tube (m)
3.9.5. g= acceleration by gravity (9.81 m/s2)