Grade 8 2nd Quarter Reviewer
Fundamentals of Earthquakes and Faulting
An earthquake is defined as the sudden shaking or movement of the Earth's crust. This geological phenomenon is primarily caused by the rapid release of energy in the Earth's interior, often triggered by the movement of molten rock. The specific point within the Earth where the earthquake starts or where the slip is initiated is known as the focus (also referred to as the hypocenter). Directly above the focus, on the surface of the Earth, is the epicenter. Shaking is most intense and likely to be greater at the epicenter or in areas near it, and the intensity generally decreases as one moves away from the epicenter.
A fault is a break or crack in the Earth's crust along which significant movement has taken place. The flat surface along which there is a slip during an earthquake is called the fault plane, and the trace of the fault on the surface is the fault line. Faults are characterized by the types of stress that form them. For instance, when rocks are compressed or pushed together, they form reverse faults or thrust faults. The process of earthquake generation is often described by scientists as a "stick and slip" process. Initially, the rocks are stuck together due to friction; however, as stress builds up, the rocks eventually slip suddenly, releasing energy in the form of seismic waves. These waves are the energies that travel through the different layers of the Earth. A fault that has displayed seismic activity in the past is classified as an active fault.
Earthquake Measurement and Government Monitoring
There are two primary ways to measure an earthquake: intensity and magnitude. The Modified Mercalli Scale is used to measure an earthquake's intensity based on the observed effects on people, structures, and the natural environment. In contrast, scales like the Richter Scale or the Moment Magnitude Scale measure the energy released. In the Philippines, the government agency tasked with identifying the intensity of earthquakes and monitoring the movement of the Earth's crust is the Philippine Institute of Volcanology and Seismology, commonly known as PHIVOLCS. Other relevant agencies included in disaster management are PAGASA (for weather and astronomical phenomena), NDRRMC (for disaster risk reduction), and the DENR (for environment and natural resources).
The Philippines is particularly prone to earthquakes because of its geographical location along the Pacific Ring of Fire, a region characterized by frequent seismic and volcanic activity. When sudden displacements occur on the sea floor due to earthquakes, landslides, or volcanic activity, a series of ocean waves known as a tsunami can be generated. Regarding safety during an earthquake, it is generally considered safer to be outside in an open area rather than remaining inside buildings, under trees, or inside vehicles. In terms of scientific advancement, while scientists can characterize the seismic risk of specific areas, they cannot yet accurately predict the exact time and location of most earthquakes.
Physics of Light and the Visible Spectrum
Light behaves in specific ways when interacting with different media. Refraction is the bending of light as it travels from one medium to another of different optical densities. When light strikes a surface like a mirror, it undergoes reflection. White light is actually composed of different colors; when it enters a prism, it undergoes dispersion, which is the separation of white light into its constituent colors (the visible spectrum). Light is classified as an electromagnetic wave situated between the infrared and ultraviolet regions of the spectrum. The constant speed of light in a vacuum is approximately .
The visible spectrum consists of various colors with distinct physical properties. Red light has the greatest wavelength and the least energy, and it is the color that is least bent (refracted) when passing through a prism. Conversely, colors like blue or violet have higher energy and shorter wavelengths. The energy of light is inversely proportional to its wavelength.
Meteorology and Tropical Cyclone Formation
Tropical cyclones require specific environmental conditions to form. They usually originate over warm ocean waters where the temperature is at least or higher. The warm ocean water heats the air above it, causing the air to rise. As the warm air rises, it creates a Low Pressure Area (LPA). Surrounding air then moves toward this area to fill the void. The rising warm air contains significant amounts of water vapor, which eventually condenses. During condensation, heat is released (latent heat), which makes the air rise even further. This continuous cycle causes more air from the surroundings to move in and start spinning, eventually leading to the birth of a tropical cyclone.
Astronomy: Comets, Asteroids, and Meteors
Comets and asteroids are small celestial bodies with distinct characteristics. Comets are icy bodies, often described as "dirty snowballs," while asteroids are rocky fragments. Most asteroids are found in the Asteroid Belt located between the orbits of Mars and Jupiter. Comets typically have highly elliptical orbits and originate from regions beyond the planets, such as the Kuiper Belt (for short-period comets) or the Oort Cloud (for long-period comets). The most famous short-period comet of the 20th century is Halley's Comet, which appeared in 1910 and 1986, and is expected to return to the night sky around the years 2061 to 2062. A notable asteroid, 2012 DA14, gained attention when it passed close to Earth on February 16, 2012.
The terminology for space rocks changes based on their location. A meteoroid is a space rock fragment before it enters the Earth's atmosphere. When a meteoroid enters the atmosphere and burns up due to friction, it creates a light phenomenon popularly known as a "shooting star" or a meteor. Friction with the atmosphere produces enough heat and light to cause the meteor to glow. If a part of the space rock survives the journey through the atmosphere and lands on the Earth's crust, it is called a meteorite. Meteor showers occur when the Earth, in its orbit around the Sun, passes through the debris-filled orbit of a comet. In a comet, the gas tail always points away from the sun due to solar winds.