Angin Siklon dan Anti Siklon

a.

Angin siklon Tahukah Anda apa yang dimaksud dengan angin siklon? Angin siklon adalah angin yang gerakannya berputar ke dalam, mengelilingi daerah tekanan minimum. Tentu Anda masih ingat dengan Hukum Buys Ballot bahwa antara lain di belahan bumi selatan angin berbias ke kiri. Gerakan angin siklun mengikuti hukum ini, yaitu: • Di belahan bumi utara perputarannya berlawanan dengan arah perputaran jarum jam. • Di belahan bumi selatan sesuai dengan arah putaran jarum jam. Perhatikan gambar 15 berikut. Gambar 1: Arah Angin Siklon di Belahan Bumi Berdasarkan bergeraknya, siklon dibedakan atas siklon tropik, siklon ekstra tropik, dan tornado. Siklon-siklon tersebut dapat terjadi: 1) Siklon tropik Siklon tropik terjadi di daerah tropis, yaitu antara 10( - 20( LU dan 10( - 20( LS. Sering terjadi di wilayah lautan daripada di daratan, misalnya di Indonesia pernah terjadi di sekitar Pulau Timor (11(LS). Mengenai wilayah pergerakan siklon tropik, dapat Anda lihat pada gambar 15. Diameter angin siklon tropik ± 100.500 km, kecepatannya antara 100 - 500 km/jam. Gradien barometernya antara 50 - 100 mb. Gambar 2: Wilayah Pergerakan Siklon Tropik Di beberapa negara badai siklon diberi nama-nama khusus sesuai dengan bahasa negara masing-masing, dan umumnya menggunakan nama wanita, antara lain: • Di Samudera Atlantik dan Pasifik Timur dinamai Hurricanes artinya Dewa Kehancuran. • Di Samudera Atlantik Barat , masyarakat Jepang menyebutnya Typhoon. • Di Filipina disebut Begieros (nama satu kota). • Di Australia disebut Willy-Willies. • Di Samudera Hindia disebut Siklon Tropik Lena (nama wanita). • Di beberapa tempat lain diberi nama Siklon Anna, Dora, Corrie, Diana, Elly dan sebagainya. 2) Siklon Ekstra Tropik Siklon ekstra tropik terjadi di daerah sedang pada lintang 35° - 65° LU dan 35° - 65° LS, yaitu di sekitar wilayah front. Tempat bertemunya massa angin barat yang panas dan angin timur yang dingin. Misalnya, Amerika Serikat dan Eropa. Tekanan udara ± 15 mb dan kecepatannya ± 30 km/jam. 3) Tornado Angin siklon tornado merupakan jenis angin yang paling cepat dan paling merusak. Tornado sering terjadi di Amerika Serikat. Diameter angin siklon tornado antara 100-500 km, panjang lintasannya mencapai 100 km. Kecepatannya mencapai 700 km/jam. Bentuk arah tornado dapat Anda perhatikan pada gambar di bawah ini. Gambar 3: Bentuk Arah Tornado

b.

Angin Anti Siklon Angin anti siklon adalah angin yang gerakannya berputar ke luar, dengan tekanan maksimum di pusatnya. Arah pergerakannya adalah sebagai berikut: • Di belahan bumi utara, putarannya searah dengan jarum jam. • Di belahan bumi selatan, putarannya berlawanan dengan arah jarum jam. Perhatikan gambar 18. Gambar 4: Arah Angin Anti Siklon di Belahan Bumi

ANGKA PENTING

The Second Law of Motion

The Second Law of Motion

When an object at rest begins to move, it has an acceleration since the velocity changes. In the same way, when an object changes its state of motion, it has an acceleration because the  velocity changes.

Whenever an unbalanced force acts on an object, it produces an acceleration on the object.

The second law of motion states that :

The unbalanced force acting on a particle is proportional to the acceleration it produces on the particle.

Fnet µ a

Fnet  = m a

m is a constant and is called the mass of the object.

Unit of Force

The second law of motion helps us to measure force using the relation :

Fnet = m a

m is the mass of the particle and it is measured in kilogram (kg).

Acceleration is measured in m/s².

There, force is measured in kg.m/s².

Kg.m/s² is called a Newton (N).

Unit of force is the Newton (N).

The amount of force that produces an acceleration of 1 m/s² on particle of mass 1 kg is called one newton.

English Conversation about Units of Measurement

Topic of  Discussion :   Units of Measurement

Satria     : Hi guys

Fuji dan Rizal  : Hi

Satria     : What are you doing here ?

Fuji        : We are discussing about our assignment about units of measurement. Have you finished it ?

Satria     : Oh no, I am forget if we have assignment. Can I join with you?

Rizal      : Of course. So, lets to discuss it.

Fuji        : Who’s know what is a measurement?

Satria     : I know that. A measurement is a comparison between an unknown quantity and a standard,right?

Fuji    : Yeah, you are right. And A physical quantity is identified by its unit of measurement. In a measurement we will use the….. the….

Rizal      : SI system..

Fuji        : Yes, good.

Satria     : Next, who can mention the units of measurement?

Fuji        : I can. The unit of length is the meter (m), the unit of mass is the kilogram (kg), the unit of time is the second (s), the unit of temperature is the kelvin (K), the unit of amount of a substance is the mole (mol), the unit of electric current is the ampere (A), the unit of luminous intensity is the candela (cd). And  units of length, mass, and time are called the fundamental units of measurements.

Satria     : That’s good…. And Units of such quantities are called derived units. Area, volume, speed are examples of physical quantities that have units that are derived from the fundamental units.

Rizal      : As an example, The unit of area is m². what else?

Fuji        : Speed = distance / time and the unit of speed is m/s.

Satria     : Yes, that’s good.

Fuji        : Okay, because our assignment was done and I’m hungry now. Let’s go to launch.

Rizal      : Let’s go..

English Conversation about Physics

Topic of  Discussion : Dimensions

Rizal      : Okay, welcome to educational discussion with me, Risaldi Putra. In this time we will discuss about dimensions of a physical quantity. Before we start our discussion, I will introduce our resource person for this time. They are Fuji Prasetyo and Bavitra. Good morning Fuji. How are you today?

Fuji        : I’m fine, thanks.

Rizal      : And how are you Bavitra? I hope you are fine too.

Bavitra   : Thank you, I’m fine.

Rizal      : Well, let’s we begin our discussion with the first question. Can you tell us what is the meaning of dimensions?

Fuji        : Okay. In physics, the dimension of quantity indicates the nature of the quantity.

Rizal      : How about you, Bavit?

Bavitra   : I think Fuji’s statement is true. In dimension, it has seven dimensions of basic quantity.

Rizal      : Can you mention it, Bavit?

Bavitra   : Okay. First, the dimension of length is L, the dimension of mass is M, the dimension of time is T, the dimension of temperature is θ, The dimension of electric current is I, the dimension of  luminous intensity is J and the  last… The dimension of amount of a substance is N.

Fuji        : And in dimensions, it has many dimension of derived quantity. An example, the dimension of acceleration. We know that the unit of acceleration is m/s². m is the unit of  length, and the dimension of length is L.  And s is the unit of time, and the dimension of time is T.  So, we get the dimension of acceleration is L/T² or LT  ̄².

Rizal      : That’s good explanation. But, has a constant dimension?

Bavitra   : A constant in physics. It has no dimension.

Rizal      : Okay. Thank you for Fuji and Bavitra. Well, we will continue our discussion after these commercial break. So, don’t go anywhere!