Fluids, Buoyancy, and Archimedes' Principle

It's professor Dave, let's learn about fluids. In chemistry we learned about the phases of matter as being solid, liquid, and gas. In this course we have been focusing on the motion of solid objects but there is much to be discussed in the way of fluids as well. A fluid is defined as any substance that can flow and alter its shape by virtue of its particles being able to move around with respect to one another. In a solid, particles are fixed in a lattice which produces a definite shape, so solids are not fluids, but liquids and gases are fluids, because the particles move freely, and fluids have certain properties that are important in physics. Certainly any fluid will exhibit some density which is mass per unit volume, represented by the Greek letter rho, not to be confused with the letter P, but another important characteristic of a fluid is its buoyancy. This is the upward force that is exerted an object by the fluid it is submerged in. You will be familiar with the buoyant force if you have ever tried to push a beach ball underwater. It is difficult to do because of the buoyant force that counteracts your applied force, but exactly how strong is the buoyant force and why do some object sink while others float? It can't have to do with size because a tiny pebble will sink while a massive cruise ship will float. The answer is outlined in Archimedes' principle. This states that any object submerged in a fluid will experience an upward buoyant force equal in magnitude to the weight of the fluid that is displaced, in other words the buoyant force will support an object if it is less dense than the fluid because the weight of the object will then be less than the weight of an equal volume of the fluid. This is why a cruise ship floats in the ocean. Steel is very dense but the air in all the cabins is not, so overall the ship is less dense than water. If you crush the ship up into a ball of equal mass, thus eliminating all the air, it would definitely sink. In this way the buoyant force can be expressed as the gravitational force of the displaced fluid which is equal to the mass of the displaced fluid times acceleration due to gravity. A floating object displaces fluid based on its mass and a sinking object displaces fluid based on its volume, so apart from the buoyant force Archimedes was also the first to understand that when an object like a person is submerged in water the volume of the water displaced must equal the volume of the object submerged, regardless of its shape. Any object with a volume of five milliliters when fully submerged will cause the water level to rise in this graduated cylinder to a reading of five milliliters more than before. This is an impressive insight for someone from ancient Greece, which is why Archimedes famously jumped out of the bathtub shouting Eureka, meaning i have found it. This is an explanation that will forever be associated with scientific discovery. Hopefully you will have some Eureka moment of your own during this course but for now, let's check comprehension. Thanks for watching, guys. Subscribe to my channel for more tutorials, support me on patreon so I can keep making content, and as always feel free to email me:

Channel: Professor Dave Explains

Views: 524,072

Keywords: classical physics, newton, force, dynamics, applied force, buoyancy, buoy, fluids, liquid, gas, density, archimedes, archimedes' principle, displacement, displaced water, weight, gravity, phases of matter, mass, volume, eureka

Id: 16HDJNoXQII

Length: 4min 16sec (256 seconds)

Published: Wed Mar 22 2017