ii. prinsip kerja katrol.pdf

5/19/2018 II. Prinsip Kerja Katrol.pdf

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LAPORANPRAKTIKUM FISIKA DASAR I

JUDUL PERCOBAAN

PRINSIP KERJA KATROL

OLEH :

N A M A :

N I M :

JURUSAN :

HARI / TANGGAL :

KELOMPOK :

ASISTEN :

LABORATORIUM FISIKA DASAR

FAKULTAS MATEMATIKA DAN ILMU PENGETAHUAN ALAM

UNIVERSITAS SRIWIJAYA

2014 /2015


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Lembar Kerja Praktikum Fisika Dasar ITA. 2014/2015 I-1

II. PRINSIP KERJA KATROL

2.1. TUJUAN PERCOBAAN

1. Melakukan percobaan yang menunjukkan prinsip kerja katrol dapat memudahkan

mengangkat beban.

2. Mampu menunjukan melalui percobaan dan perhitungan perbedaan keuntungan

mekanik dengan menggunakan beberapa katrol.

2.2. ALAT DAN BAHAN

1. Katrol Tunggal dan Katrol Ganda

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2. Tali Nilon

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3. Neraca Pegas.

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4. Statif.

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5. Beban.

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2.3. DASAR TEORI

Pesawat sederhana digunakan untuk melipatgandakan gaya atau mengubah arah gaya.

Jika peswat sederhana melipatgandakan gaya, maka gaya yang dikeluarkan lebih kecil

dibandingkan dengan gaya yang diperlukan untuk melakukan suatu pekerjaan tanpa bantuan

pesawat sederhana. Besaran yang menyatakan pelipatgandaan hasil dari suaru peswat sederhana

terhadap gaya atau jarak perpindahan disebut keuntungan mekanis.

Salah satu bentuk pesawat sederhana adalah katrol. Katrol adalah alat berupa roda yang

dapat berputar pada porosnya. Untuk menggunakan katrol diperlukan tali atau mata rantai.

Secara umum katrol dikelompokkan menjadi dua yaitu: katrol tetap dan katrol bergerak. Dalam

pemakaian seringkali digabungkan beberapa katrol yang selanjutnya disebut sebagai sistem

katrol.

Gambar 1. Macam-macam katrol

Tinjau gambar 1a, untuk mengangkat beban seberat FB dengan cara menarik tali dengan

gaya sebesar FK. Pada kontrol tetap (Gambar 1a) hanya terdapat satu penggal tali yang

menahan berat beban, maka besar gaya Fk , untuk menarik beban sama dengan berat FB atau :

FB = Fk

Penggunaan satu katrol tetap hanya mengubah arah gaya kuasa, sehingga keuntungan

yang diperoleh saat menggunakan adalah memudahkan pengangkutan benda saja. Pada

pemakaian satu buah katrol bergerak, beban yang akan diangkat digantungkan pada katrol

seperti Gambar 1b. Gaya berat FB, ditahan oleh dua buah penggal tali, maka

FB = 2 Fk

Keuntungan mekanis dengan menggunakan katrol bergerak adalah perbandingan antara besar

gaya beban FB dan gaya kuasa Fk.

Keuntungan Mekanis = FB / Fk = 2


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Jelas bahwa untuk mengangkat suatu benda dengan satu katrol bergerak, cukup

mengerjakan gaya yang diperlukan untuk mengangkat benda tersebut jika tanpa

menggunakan bantuan katrol. Katrol bergerak (Gambar 1c) juga sering dipergunakan. Gaya

berat FB, di tahan oleh dua buah penggal tali, maka

FB = 2Fk

Keuntungan mekanis pada sistem katrol ini adalah perbandingan antara besar gaya beban dan

gaya kuasa.

Keuntungan Mekanik = FB / Fk = 2

Sehingga untuk mengangkat benda sistem katrol 4c cukup menggunakan gaya berat

benda. Perbedaan antara sistem katrol ini dengan satu katrol bergerak adalah arah tarik Fk.

Gaya tarik pada sistem katrol ini mengarah ke bawah sehingga akan lebih memudahkan

pekerjaan, bila dibandingkan dengan penggunaan satu katrol bergerak saja yang arah tariknya

ke arah atas.

Seringkali berat beban yang kita pindahkan mencapai beberapa ton. Untuk mengangkat

nya kita gunakan katrol ganda/katrol majemuk (Gambar 1d). Katrol majemuk merupakan

gabungan dari beberapa katrol diam dan katrol bergerak.

Seperti tampak pada gambar 1d kita akan menarik tali dengan gaya Fk agar beban berat

FB dapat terangkat. Gaya berat FB besarnya sama dengan gaya

gaya bekerja pada sejumlah

penggal tali yang menahan berat beban.

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2.4. PROSEDUR PERCOBAAN

1. Tentukan berat dari beberapa beban yang digunakan dengan menggunakan neraca pegas.

2. Gantungkan katrol tunggal ke peyangga (statif) (seperti Gambar 1.a)

3. Hubungkan seutas tali ke katrol dengan satu ujung tali diikatkan pada beban dan ujung

yang lainnya dipegang.

4. Tarik tali yang menghubungkan beban dan katrol tersebut hingga beban terangkat.

5. Catat berat beban sekarang.

6. Ulangi langkah 1 s/d 4 untuk katrol ganda. (seperti Gambar 1.c dan 1.d)

7. Lakukan juga untuk katrol digantungkan ke tali (seperti Gambar 1.b).

8. Lakukan dalam satu keadaan minimal 10 kali.


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2.5. TUGAS PENDAHULUAN

1. Apa yang dimaksud pesawat sederhana? Sebutkan?

2. Sebutkan kegunaan katrol pada kehidupan kita.

3. Mengapa dalam mengangkat beban yang berat orang sering menggunakan katrol.

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No.Massa Beban (kg)

I II III

1.

2.

3.

4.

5.

No.Massa Beban (kg)

I II III

1.

2.

3.

4.

5.

2.6. DATA HASIL PENGAMATAN

A. Massa Beban

Tabel 1. Tanpa Katrol Tabel 2. Katrol Tetap

No.Massa Beban (kg)

I II III

1.

2.

3.

4.

5.

Tabel 3. Katrol Bergerak Tabel 4. Katrol Ganda

No.Massa Beban (kg)

I II III

1.

2.

3.

4.

5.

Tabel 5. Katrol Majemuk

No.Massa Beban (kg)

I II III

1.

2.3.

4.

5.


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No.Gaya (N)

I II III

1.

2.

3.

4.

5.

No.Gaya (N)

I II III

1.

2.

3.

4.

5.

B. Gaya

Tabel 1. Tanpa Katrol Tabel 2. Katrol Tetap

No.Gaya (N)

I II III

1.

2.

3.

4.

5.

Tabel 3. Katrol Bergerak Tabel 4. Katrol Ganda

No.Gaya (N)

I II III

1.

2.

3.

4.

5.

Tabel 5. Katrol Majemuk

No.Gaya (N)

I II III

1.

2.

3.

4.

5.


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2.7 PENGOLAHAN DATA...............................................................................................................................................

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2.9. TUGAS AKHIR

1. Tentukan selisih berat beban setelah dengan sebelum menggunakan katrol dari

masing-masing beban.

2. Berapa persen selisih berat beban dengan menggunakan katrol tersebut.

3. Hitung Gaya yang kita berikan untuk menahan beban dengan menggunakan katrol

dari masing-masing percobaan secara teori.

4. Bandingkan hasil praktek dengan hasil perhitungan secara teori.

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2.10. KESIMPULAN

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