Notes

Science

Lesson 1
Changes on Earth's Surface

Weathering

Rocks on Earth's surface undergo weathering. Weathering is the process of rocks and minerals break down into smaller pieces over time. This can happen through physical or chemical means, such as wind, water, or acids. The result of weathering is that the once solid rock becomes weaker and more easily eroded.

Rocks on Earth's surface are broken down by two types of weathering, mechanical weathering, and chemical weathering. The breakdown of rocks may result from the actions of gravity, water, wind, ice, plants, animals, people, and chemical reactions.


Mechanical Weathering

Mechanical weathering is a physical process that breaks down rocks into smaller pieces. Gravity, water, people, wind, plants, and animals are agents of mechanical weathering. Other examples of mechanical weathering include plants growing in cracks and exerting pressure, and rocks rubbing against each other due to wind or water movement. Over time, mechanical weathering can contribute to the formation of soil. This can also happen by frost wedging which happens when water freezes and expands in a crack in the rock, causing it to break apart.

Windblown sand mechanically weather rocks by abrasion. Abrasion is the wearing away of rocks by solid particles carried by wind, water, or other forces. This process usually happens when two surfaces come in contact with each other and rub off some material from one or both surfaces. For example, when rocks scrape against one another and wear away their surfaces, this is an abrasion. Due to abrasion, the size and shape of the objects can change as their surface layers are removed.

Animals dig and break rocks in the process of burrowing. Burrowing animals, such as earthworms, can dig holes into rocks or make existing cracks bigger. Other examples of burrowing animals are rats, rabbits, and moles.

Plants, too, can cause weathering. You will see roots of trees break sidewalks. pavements, or even plant boxes. When seeds that fell through cracks in rocks germinate and grow, they eventually break the rock into pieces.


Chemical Weathering

Chemical weathering is the process by which rocks and minerals break down as a result of chemical reactions. The primary agents of chemical weathering are water, oxygen, and acid. Over time, these agents can dissolve or change the composition of rocks and minerals, making them more vulnerable to physical weathering. Chemical weathering plays an important role in soil formation and contributes to the Earth's carbon cycle.

Oxygen combines with minerals and metals to form oxides in a process called Oxidation. For example, iron in rocks combines with oxygen to form rust, which is an oxide of iron. The reddish color that can be seen on some rocks is an indication that oxidation has occurred. This is similar to the oxidation or rusting that occurs in metals.

Acids are the most reactive chemical weathering agents. They easily react with and decompose the minerals in rocks. Sulfuric and hydrofluoric acids from volcanic and hot spring activities can also weather rocks.

Carbon dioxide dissolves in water to form a weak acid called carbonic acid. Carbonic acid is the most abundant natural acid and is also capable of dissolving minerals in rocks. Rainwater usually contains dissolved carbon dioxide and is slightly acidic.

Gas emissions from factories also contain sulfur oxides, which, when dissolved in rainwater, form strong acids such as sulfuric acid. Rain containing sulfuric acid becomes acid rain, the major cause of weathering in cities. It slowly wears away buildings and statues. It also damages roads and bridges.

There are several factors that influence the speed of A statue that has weathered due chemical weathering. to acid rain

1 Mineral content - Some minerals, such as calcite found in limestone, weather more rapidly. Other minerals, such as quartz, do not weather at all.

2. Climate - A warm and moist climate promotes chemical weathering and speeds up the reaction between the acid and the mineral. Gentle slopes and abundant vegetation, which retain rainwater longer, hasten the process of chemical weathering too.

3. Exposed surface area - The greater the area exposed, the more chemical weathering takes place. When rocks break apart, new surfaces become exposed to the chemical agents.


Erosion
Soil is transported from one place to another in a process called erosion.
Wind, running water, waves, and gravity cause erosion. These are called agents of erosion. An agent of erosion is a material or force that moves sediments from one place to another.



Lesson 2
Weather

Weather is the condition of the atmosphere. It can be cold or hot, wet or dry, and clear or cloudy. Meteorology is the branch of science that studies weather. People who study weather are called meteorologists.


Weather Disturbances

Weather Disturbances Thunderstorm

Most thunderstorms occur in the afternoon and in the evening. It may last from 30 minutes to an hour. Thunderstorms are accompanied by thunder and lightning. Since light travels faster than sound, you see the flash of lightning first before you hear the sound of thunder.

Thunderstorms occur when masses of warm, moist air along Earth's surface are rapidly forced upward into cold, dry layers. As warm air is forced upward, it cools and condenses, forming cumulonimbus clouds. Thunderstorms are characterized by gusty winds, heavy rain, and lightning.

During a thunderstorm, areas of positive and negative electrical charges build up in the storm clouds. Lightning is produced when a spark of electricity jumps between these clouds and the ground. The lightning causes the air to expand explosively. A lightning is always accompanied by thunder, a loud sound caused by the rapid expansion of air.

Unlike other weather disturbances, thunderstorms last for just a few minutes or hours. A flash flood sometimes occurs after a strong rain.



Tornado

A tornado is a whirling, funnel-shaped column of air that develops from low, heavy cumulonimbus clouds, which are associated with extreme weather such as thunderstorms. The area at the bottom of this funnel of swirling air has an extremely low air pressure. When this low-pressure point touches the ground, it acts like a giant vacuum cleaner. Tornadoes generally last only a few minutes, but they can be as devastating as violent storms. Tornadoes have very strong winds that can reach speeds of more than 500 kilometers per hour (kph).


Tropical Cyclone

Tropical cyclones are characterized by heavy rains and winds and are formed over warm ocean water. They are also called hurricanes or typhoons, depending on where they occur.


Air near the center is forced upward and flows outward, forming clouds. As it moves up, the clouds grow higher and larger, causing pressure to drop and winds to spin faster. Winds in tropical cyclones can go up to over 250 kph, which can cause extreme damage. The air is calm at the center of the tropical cyclone. This calm center is called the eye of a storm.

In the North Atlantic Ocean and Northeast Pacific Ocean, tropical cyclones are called hurricanes.
In the South Pacific Ocean and in the Indian Ocean, a tropical cyclone is simply called a cyclone. Cyclones affect Africa, parts of Australia, and the Middle East.

The area of the Northwest Pacific Ocean, a tropical cyclone is called a typhoon. Typhoons begin near the equator and move eastward, gathering intensity and size. Typhoons are given names to make communication easy between the weather forecaster and the general public. The Philippines experiences an average of 20 typhoons per year.

The Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) classifies them into five categories. The fifth category, super typhoon (STY) was added in 2015

a. tropical depression (TD), with wind speed of up to 61 kph;

b. tropical storm (TS), with wind speed of 62 to 88 kph;

c. severe tropical storm (STS), with wind speed ranging from 89 to 117 kph;

d. typhoon (TY), with wind speed of 118 kph to 220 kph; and

e. super typhoon (ST), with wind speed of more than 220 kph.


PAGASA releases Public Storm Warning Signals (PSWS) to warn the people. These signals are raised when a tropical cyclone is expected to enter the Philippine Area of Responsibility (PAR).



Public Storm Warning Signals



PSWS #1

Tropical cyclone winds of 30-60 kph are expected within the next 36 hours. (Note: If a tropical cyclone forms very close to the area, then a shorter lead time is seen on the warning bulletin.)

PSWS #2

Tropical cyclone winds of 61-120 kph are expected within the next 24 hours.

PSWS #3

Tropical cyclone winds of 121-170 kph are expected within the next 18 hours.

PSWS #4

Tropical cyclone winds of 171-220 kph are expected within 12 hours.

PSWS #5

Tropical cyclone winds of more than 220 kph are expected within 12 hours.

Safety measures before, during, and after a typhoon must be practiced. These measures include listening to weather reports, preparing food and light sources, and reinforcing house structures.