Fluida dan Hukum Archimedes

BAB I

PENDAHULUAN

A.        Latar Belakang

Benda padat mempertahankan bentuk dan ukuran yang tetap; bahkan jika sebuah gaya yang besar diberikan pada sebuah benda padat, benda tersebut tidak langsung berubah bentuk atau volumenya. Benda cair tidak memperthankan bentuk yang tetap melainkan mengambil bentuk tempat yang ditempatinya, tetapi seperti benda padat benda cair tidak langsung dapat ditekan, dan perubahan volume yang signifikan terjadi jika gaya diberikan gaya yang besar.

Gas tidak memiliki bentuk maupun volume yang tetap, gas akan menyebar untuk memenuhi tempatnya. Sebagai contoh, ketika udara dipompa ke dalam ban mobil, udara tersebut tidak seluruhnya mengalir ke bagian bawah ban seperti zat cair; melainkan menyebar untuk memenuhi seluruh volume ban karena zat cair dan gas tidak mempertahankan bentuk tetap, keduanya memiliki kemampuan untuk mengalir; dengan demikian kedua-duanya sering disebut sebagai fluida.

B.        Tujuan Penulisan

Dari penyusunan makalah ini, penyusun mengharapkan dapat memberikan sumbangsi dalam peningkatan pengetahuan pembaca mengenai Fluida khususnya. Berikut tujuan-tujuan lain penyusun dalam penyusunan makalah ini.

a.         Untuk mengetahui proses Tekanan yang dilakukan Fluida.

b.         Untuk mengetahui Bagaimana pemanfaatan hal tersebut.

c.          Memberikan informasi kepada pembaca mengenai Fluida.

C.        Metode Pengumpulan Data

Metode yang digunakan penyusun untuk mendapatkan data yaitu dengan cara mengidentifikasi dari beberapa sumber-sumber yang terpercaya. Dengan terlebih dahulu mengadakan klasifikasi terhadap bahan-bahan yang didapatkan demi mendapatkan hasil yang diinginkan.

BAB II

PEMBAHASAN

A.        Massa Jenis dan Gravitasi Khusus

Massa jenis (density), ρ, sebuah benda (ρ adalah huruf kecil dari abjad Yunani “rho” didefinisikan sebagai massa per satuan volume:

ρ = m/V ,

dimana m adalah massa benda dan V  merupakan volumenya.

Kerapatan alias massa jenis fluida homogen (sama) pada dasarnya berbeda dengan kerapatan zat padat homogen. Besi atau es batu misalnya, memiliki kerapatan yang sama pada setiap bagiannya. Berbeda dengan fluida, misalnya atmosfer atau air. Pada atmosfer bumi, makin tinggi atmosfir dari permukaan bumi, kerapatannya semakin kecil sedangkan untuk air laut, misalnya, makin dalam kerapatannya semakin besar. Massa jenis alias kerapatan dari suatu fluida homogen dapat bergantung pada factor lingkungan seperti temperature (suhu) dan tekanan.

Satuan Sistem Internasional untuk massa jenis adalah kilogram per meter kubik (kg/m³). Untuk satuan CGS alias centimeter, gram dan sekon, satuan Massa jenis dinyatakan dalam gram per centimeter kubik (gr/cm³).

Berikut ini data massa jenis dari beberapa zat.

Zat	Kerapatan (kg/m3)
Zat Cair
Air (4o C)	1,00 x 103
Air Laut	1,03 x 103
Darah	1,06 x 103
Bensin	0,68 x 103
Air raksa	13,6 x 103
Zat Padat
Es	0,92 x 103
Aluminium	2,70 x 103
Besi & Baja	7,8 x 103
Emas	19,3 x 103
Gelas	2,4 – 2,8 x 103
Kayu	0,3 – 0,9 x 103
Tembaga	8,9 x 103
Timah	11,3 x 103
Tulang	1,7 – 2.0 x 103
Zat Gas
Udara	1,293
Helium	0,1786
Hidrogen	0,08994
Uap air  (100 oC)	0,6

Kerapatan zat yang dinyatakan dalam tabel di atas merupakan kerapatan zat pada suhu 0^o C dan tekanan 1atm (atmosfir alias atm = satuan tekanan.

Gravitasi khusus suatu zat dapat diperoleh dengan membagi kerapatannya dengan 10³ kg/m³ (kerapatan air pada suhu 4^o C). Gravitasi khusus tidak memiliki satuan dan dimensi.

Apabila kerapatan suatu benda lebih kecil dari kerapatan air, maka benda akan terapung. Gravitasi khusus benda yang terapung lebih kecil dari 1. Sebaliknya jika kerapatan suatu benda lebih besar dari kerapatan air, maka gravitasi khususnya lebih besar dari 1. Untuk kasus ini benda tersebut akan tenggelam.

Berat jenis suatu zat merupakan perbandingan berat zat tersebut terhadap volumenya. Satuan sistem internasional untuk berat jenis adalah N/m³.

B.        Tekanan pada Fluida

Tekanan didefinikan sebagai gaya per satuan luas, dimana gaya F dipahami bekerja tegak lurus terhadap permukaan A:

Tekanan = P =   F/A

Dengan demikian gaya yang bekerja pada luas daerah tersebut adalah F = mg = ρAhg, di mana Ah adalah volume  kolom, ρ adalah massa jenis zat cair (dianggap konstan), dan g adalah percepatan gravitasi. Tekanan P, dengan demikian adalah:

P = ρgh

Dengan demikian, tekanan berbanding lurus dengan massa jenis zat cair, dan dengan kedalaman di dalam zat cair. Pada umumnya, tekanan pada kedalaman yang sama dalam zat cair yang serba sama adalah sama.

C.        Prinsip Pascal

Prinsip Pascal menyatakan bahwa tekanan yang diberikan pada cairan dalam suatu tempat tertutup akan diteruskan sama besar ke setiap bagian fluida dan dinding wadah.

Fluida ( zat alir ) adalah zat yang dapat mengalir, misalnya zat cair dan gas. Prinsip Pascal menyatakan bahwa tekanan yang diberikan pada fluida dalam sutu tempat akan menambah tekanan keseluruh dengan besar yang sama.

Tekanan yang dilakukan pada zat cair akan diteruskan ke semua arah sama.

P₁ = P₂                F₁/A₁ = F₂/A₂

D.        Hukum Archimedes

Benda di dalam zat cair akan mengalami pengurangan berat sebesar berat zat cair yang dipindahkan.

Tiga keadaan benda di dalam zat cair:

a.    tenggelam: W>Fa Þ rb > rz

b.    melayang: W = Fa Þ rb = rz

c.    terapung: W=Fa Þ rb.V=rz.V' ; rb<rz

Dimana :

W = berat benda
Fa = gaya ke atas = rz . V' . g
rb = massa jenis benda
rz = massa jenis fluida
V = volume benda
V' = volume benda yang berada dalam fluida

Akibat adanya gaya ke atas ( Fa ), berat benda di dalam zat cair (Wz) akan berkurang menjadi:

Wz = W - Fa

Wz = berat benda di dalam zat cair

Tegangan Permukaan

Tegangan permukaan ( g) adalah besar gaya ( F ) yang dialami pada permukaan zat cair persatuan panjang(l)

g = F / 2l

Kapilaritas

Kapilaritas ialah gejala naik atau turunnya zat cair ( y ) dalam tabung kapiler yang dimasukkan sebagian ke dalam zat cair karena pengarah adhesi dan kohesi.

y = 2 g cos q / r g r

y = kenaikan/penurunan zat cair pada pipa (m)

g = tegangan permukaan (N/m)

q = sudut kontak (derajat)

p = massa jenis zat cair (kg / m³)

g = percepatan gravitas (m / det²)

r = jari-jari tabung kapiler (m)

DAFTAR PUSTAKA

Giancoli, C. Douglas. 1998. Fisika. Jakarta: Erlangga

Nulhakim, Lukman. 2007. Belajar Efektif Fisika. Jakarta: PT. Intimedia Cipta Nusantara

Definition, Types, and Function of Verbs

A.      Definition of Verbs

What’s a verb? Verbs are words that usually express an action.

B.      Types of Verbs

Classified by Complement of Verb

The types of verbs describe here differ according to the kind of complete the may have. Because these types may cut across each other, a verb may belong to more than one type.

1.       Predicating or Linking Verbs

Predicating verb is the chief word I the predicate that says something about the subject. The predicating word (or predicator) has traditionally been called a verb of “action” (babies cry; She wrote a letter), but has actually been interpreted to include most non-action verbs that are not linking verbs (for example, I remember him; She needs more money). The term event is probably a more exact way to refer to what is denoted by a predicating verb, and is the term that will be favored in this book.

A linking verb is a verb of incomplete predicating; it merely announces that real predicate follows. The important word in the complement is usually an adjective (The girl is pretty) or a noun (She is a pretty girl). The –ly adverbs of manner  (quickly, angrily) are not used with linking verbs. The more common linking verbs are appear, be, become, get (in the sense of become), look, remain, seem.

Also functioning as linking verbs are the verbs of perception –feel, taste, smell, sound.

        The milk tastes sour.

        The rose smells sweet.

Included among the linking verbs are certain verb-adjective combinations that express a state. Some of these combinations are actually little more than idioms. Many of these verbs have the force of become-blow (open), blush (red), break (loose), grow (worse), fall (ill), prove (wrong), stand (quiet), turn (pale), wax (eloquent).

The linking verbs are often subdivided by modern grammarians into be and all others. One of the most important differences is that, whereas the other linking verbs are followed mostly by predicate adjectives, be may be followed by many types of complement:

Adjective Noun Adverb Prepositional Phrase Noun Clause Infinitive Phrase Gerund Phrase

He is handsome. He is a handsome boy. The man is here. (usually place) Mary is in the house. (Some of the prepositional phrase after be are idiomatic: We are of the same opinion; that is out of the question.) We are what we eat. The problem is to find the right house. The problem is finding the right house.

In addition to differing from other linking verbs in the type of complements it takes, be also differs from all other verbs with respect to the position of adverb used with it, and with respect to its manner of forming questions and negatives. For this reason some grammarians separate be still further from other verbs and place it in a special category all by itself.

2.       Transitive or Intransitive Verbs

A transitive verb takes a direct object (He is reading a book); an intransitive verb does not require an object (He is walking in the park). Only transitive verbs may be used in the passive voice (The book was returned by him quickly). All linking verbs are intransitive.

Transitive verbs may take more than one object:

Indirect object and direct object Direct object and objective complement

He gave his wife a present They elected Mr. Smith president

Many verbs may be used either transitively (He was writing a letter) or intransitively (He was writing at the library). Other verbs are transitive only and must be followed by an object –have, like, need, owe, remember.

Some intransitive verbs have developed transitive uses, especially in a causative sense:

        He always walks his dog at night (=causes his dog to walk)

        The railroad runs additional trains during holiday (=causes additional trains to be run)

A few intransitive verbs are used transitively with cognate objects –run a race, dream a strange, live a good life.

Other intransitive verbs have different forms for transitive use.

Intransitive	Transitive
Lie Rise Sit	Lay Raise Set	The book is lying on the table. He laid the book on the table. The sun rises in the east. The student raised his hand Please sit down She set the chair in the corner

Some transitive verbs may be used intransitively to express a passive idea. Their subjects usually denote things rather than person.

        The book sold out (=were sold out) in a week.

        The bread baked (=was baked) too long

        Such houses rent (=are rented) easily.

Many verb-preposition combinations may be regarded as transitive, since they can be used in the passive.

Active Passive

He looked up all the new words. All new words were looked up by him.

A small class verbs, called middle verbs, are transitive in that they take a formal object, but intransitive in that they cannot be used in the passive voice –among them are cost, have, last, resemble, weigh.

        Bob resembles his father

        This book costs $8.00

The expressions after verbs like cost and weigh may also be consider as adverbial expressions of quantity rather than as direst objects. (They are sometimes called adverbial objects).

3.       Reflexive Verbs

A reflexive verb requires one of the compounds with –self (reflexive pronoun) as its object –express oneself, wash oneself, pride oneself, avail oneself. Some verbs may be used with or without the reflexive pronoun object –He washed (himself) and dressed (himself) quickly. Reflexive verbs often have a non-reflexive use also, and can take objects that do not refer back to the subject –She washed the child and then dressed him quickly.

  

Classified by Form of Verb

4.       Auxiliary or Lexical Verbs

Two or more words may be joined together into a single verb phrase that functions as the full verb of the predicate. The first part of the verb phrase is the auxiliary (or auxiliaries), and the second part is the lexical verb (will be, arriving). The lexical verb carries the chief burden of semantic content. The auxiliary verb acts as a “helping” verb to the lexical verb by adding either (1) a structural element that marks differences in tense, voice, mood, and aspect, or that signals questions and negatives; or (2) a semantic coloring such as ability, possibility or necessity (modal auxiliary).

Some verbs used as auxiliaries may also occur independently –be, have, do. Other verbs function chiefly as auxiliaries and must be used with lexical verb –shall, will, can, must, may, should, would, could, might.

Auxiliaries combine with lexical verbs that are in simple (unchanged) form (will open), in –ing form (is opening), or in –ed  form (was opened). The number of auxiliaries used with a lexical verb varies. A lexical verb may have no auxiliaries (he opens, he opened), one auxiliary (he will open), two auxiliaries (he has been opening), or three auxiliaries (he may have been opening). Agreement with the subject occurs in the first auxiliary only. Only be, have, do, the verbs that may be used independently, can indicate person and number.

5.       Finite of Non-Finite Verbs

The form for these verbs is determined by the function which the verb has in a sentence. A finite verb is a lexical verb with or without auxiliaries that acts as the full verb in the predicate. It is limited by all the grammatical properties a verb may have-person, number, tense, voice, etc.

Non-finite (or infinite) verbs are incomplete verb forms that function as other parts of speech than verbs. The consist of the infinitive forms (to + the simple form of the verb) and the participial –ing or –ed forms. Thus, in The boy talking to the teacher is my brother, talking is a participle used as an adjective to modify boy. In He likes talking to the teacher, talking is a noun (a gerund) used as the object of likes. He non-finite forms, which are also called verbals, are not limited by person or number, but they have voice and some tense.

Another kind of classification of verbs by form may be made in terms of compound semantic units. Such compounds may consist of two words joined together into one, or of two separate parts.

C.      Function of Verbs

The verb functions as the grammatical center for the predication about the subject. As we have seen, it may be a grammatical center expressing mere linkage, or it may be the strongest predicating word in the central core of the sentences. The verb is so basic that other functions (subject, object, complement) are determined in relation to it.