Stability of Objects

Stability can be defined as the ability of objects to return to its original state if disturbed. If an object is more stable, it can be able to resist larger forces. Objects that are stable will not topple over because they have their weight concentrated low down. This point is called the centre of gravity and the lower it is, the more stable is the object.

       An object is stable when its centre of gravity is located over its base. The lower an object’s centre og gravity is, complete to the height, the less likely it is to fall. The higher the object, the less stable it is. It means, the taller a structure is, the more it moves when forces like wind acts on it. The other factor that affects stability is based area. The wider the base area, the more stable the object is. The wider the bass of support, the easier it is to maintain balance.

Here are some examples of everyday life situations used to explain how base area and height affect the stability of a structure.

Based area	Height
* A heavy weight lifter spreads his legs to add stability.	* Big animals such as elephant and rhinoceros have short legs to lower the centre of gravity for stability.
* The wide distance between the wheels of a racing car is to increase the base area of the car in order to maintain its stability when it is moving fast.	* Racing cars are designed with low bodies to lower the centre of gravity.
* Laboratory apparatus such as a conical flask and tripod stand has a wide base for the purpose of stability.	* Boat passengers are advised to sit when the boats for stability.
The cross sectional * A raft is more stable than a kayak because a kayak has less base area

The shapes of objects in structure

• Many objects around us are made up of basic shapes.
• The following diagrams are some of the basic shapes that can be found around us.

1. Sphere

2. Hemisphere

3. Cylinder

4. Cone

5. Cube

6. Pyramid

7. Cuboid

Chapter 12-Strength and Stability

The two most important things that engineers or architects need to look at when building something is its strength and stability. The bigger the objegt that they want to build, the more important it is for the object to be stranger and more stable. For example, stronger materials such as steel and concrete are need when building a big bridge that allows thousands of vehicles to travel on it at the same time. However, less stronger materials such as wood can be used to build smaller bridges that are used by people or fewer vehicles. Apart from the materials used, the shape of the object is important as it provides stability for the object. This is especially important in the construction of tall buildings such as the Petronas Twin Towers ( KLCC ) and the Kuala Lumpur Tower.

Moon Phase

The Phases of the Moon

The Phases of the Moon

The revolution of the Moon around the Earth makes the Moon seems to change its shape in the night sky. This is caused by the different angles we see from the bright part of the Moon’s surface. This is called “phases” of the Moon. Of course, the Moon does not generate any light itself; it just reflects the light of the Sun. The Moon goes through four major shapes during a cycle that repeats itself every 28 days. These phases follow the sequence of their occurrence,

      

Moon Phase Views...

For practical purposes, phases of the Moon and the percent of the Moon illuminated are independent of the location on the Earth from where the Moon is observed. That is, all the phases occur at the same time regardless of the observer's position. New Moon, First Quarter, Full Moon, and Last Quarter phases are considered to be primary phases and their dates and times are published in almanacs and on calendars. The two crescent and two gibbous phases are intermediate phases, each of which lasts for about a week between the primary phases, during which time the exact fraction of the Moon's disk that is illuminated gradually changes.

New Moon - The Moon's unilluminated side is facing the Earth. The Moon is not visible (except during a solar eclipse).The lighted side of the Moon faces away from the Earth.  This means that the Sun, Earth, and Moon are almost in a straight line, with the Moon in between the Sun and the Earth.  The Moon that we see looks very dark. Waxing Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. This Moon can be seen after the New Moon, but before the First Quarter Moon.  The crescent will grow larger and larger every day, until the Moon looks like the First Quarter Moon. First Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. The right half of the Moon appears lighted and the left side of the Moon appears dark.  During the time between the New Moon and the First Quarter Moon, the part of the Moon that appears lighted gets larger and larger every day, and will continue to grow until the Full Moon. Waxing Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is increasing. This Moon can be seen after the First Quarter Moon, but before the Full Moon.  The amount of the Moon that we can see will grow larger and larger every day.  ("Waxing" means increasing, or growing larger.) Full Moon - The Moon's illuminated side is facing the Earth. The Moon appears to be completely illuminated by direct sunlight. The lighted side of the Moon faces the Earth.  This means that the Earth, Sun, and Moon are nearly in a straight line, with the Earth in the middle.  The Moon that we see is very bright from the sunlight reflecting off it. Waning Gibbous - The Moon appears to be more than one-half but not fully illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. This Moon can be seen after the Full Moon, but before the Last Quarter Moon.  The amount of the Moon that we can see will grow smaller and smaller every day. ("Waning" means decreasing, or growing smaller.) Last Quarter - One-half of the Moon appears to be illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. Sometimes called Third Quarter.  The left half of the Moon appears lighted, and the right side of the Moon appears dark.  During the time between the Full Moon and the Last Quarter Moon, the part of the Moon that appears lighted gets smaller and smaller every day. It will continue to shrink until the New Moon. Waning Crescent - The Moon appears to be partly but less than one-half illuminated by direct sunlight. The fraction of the Moon's disk that is illuminated is decreasing. This Moon can be seen after the Last Quarter Moon and before the New Moon.  The crescent will grow smaller and smaller every day, until the Moon looks like the New Moon.

Days and Night

The Discovery of Day and Night

Astronomy was first studied by ancient Egyptians in their exploration of the Moon, stars and other objects in space. The ancient Egyptians were the first explorers to find out what causes day and night. They studied how the Sun and the Moon travelled across the sky by observing their different movements. The early astronomers discovered that the Earth contains an imaginary line, called an axis, that passes through the centre of the Earth. This axis also passed between the North and South Poles.

Occurrence of Day and Night

The Earth rotates on its axis. This rotation causes day and night. When the Earth faces the Sun, the part of the Earth experiences daytime. On the other hand, when the Earth faces away from the Sun, the part of the Earth experiences night-time. Thus, day being on one side of the Earth and night is on the other side of the Earth. Each rotation on the Earth’s axis takes about 24 hours to complete. This 24 hour cycle includes both day and night, and makes one day.

The Solar System