Understanding Fire and Water in Firefighting
Fire Classification and the Fire Tetrahedron
Fire Classifications in Chile (NCh 934)
Class A: Ordinary Combustibles
These fires involve materials like wood, paper, cloth, rubber, and resins. The symbol is the letter A on a green triangle.
Class B: Flammable Liquids and Gases
These fires involve flammable or combustible liquids, flammable gases, greases, and paints. The symbol is the letter B on a red square.
Class C: Electrical Fires
These fires involve energized electrical equipment. Safety requires using
Read MoreThe History and Evolution of Cement: From Natural Cements to Modern Portland Cement
History of Cement
Early Developments
Apparently unaware of Smeaton’s work, the same principle was identified by Frenchman Louis Vicat in the first decade of the nineteenth century. Vicat went on to devise a method of combining chalk and clay into an intimate mixture, and, burning this, produced an “artificial cement” in 1817[14] considered the “principal forerunner”[3] of Portland cement and “…Edgar Dobbs of Southwark patented a cement of this kind in 1811.”[3]
In Russia, Egor Cheliev created a new
Read MoreGravitational Force and Potential Energy: A Comprehensive Guide with Examples
4. The gravitational force between you and the moon at its initial position (directly opposite of Earth from you) is
where
is the mass of the moon,
is the distance between the moon and the Earth, and
is the radius of the Earth. At its final position (directly above you), the gravitational force between you and the moon is
.
(a) The ratio of the moon’s gravitational pulls at the two different positions is
Therefore, the increase is 0.06898, or approximately, 6.9%.
(b) The change of the gravitational
Read MoreGravitational Force and Potential Energy: A Comprehensive Guide with Examples
4. The gravitational force between you and the moon at its initial position (directly opposite of Earth from you) is
where
is the mass of the moon,
is the distance between the moon and the Earth, and
is the radius of the Earth. At its final position (directly above you), the gravitational force between you and the moon is
.
(a) The ratio of the moon’s gravitational pulls at the two different positions is
Therefore, the increase is 0.06898, or approximately, 6.9%.
(b) The change of the gravitational
Read MoreFluid Mechanics: Buoyancy, Pressure, and Fluid Flow
5. Let the volume of the expanded air sacs be Va and that of the fish with its air sacs collapsed be V. Then
where ρw is the density of the water. This implies
ρfishV = ρw(V + Va) or (V + Va)/V = 1.08/1.00,
which gives Va/(V + Va) = 0.074 = 7.4%.
7. (a) The pressure difference results in forces applied as shown in the figure. We consider a team of horses pulling to the right. To pull the sphere apart, the team must exert a force at least as great as the horizontal component of the total force determined
Read MoreUnderstanding Electrical Circuits, Resistance, and Ohm’s Law
Electric Circuits: Concepts and Applications
An electrical circuit is a group of elements connected to each other in which a transference and transformation energy process is created by the motion of electric charges.
An electrical circuit is formed by the following elements:
Elements of an Electrical Circuit
- Loops: Closed trajectory in a circuit.
- Net: Closed trajectory that does not have another closed trajectory inside.
- Nodes: Connection between 2 or more electrical elements.
- Branch: Any electrical element