4. modul praktikum fisika dasar i

Penuntun Praktikum Fisika Dasar I 1
CARA PENGGUNAAN ALAT UKUR
PRAKTIKUM FISIKA DASAR I
JANGKA SORONG
Jangka sorong adalah alat pengukur tebal suatu benda yang sangat kecil sekali,
kepekaannya mencapai 0,1 mm. Alat pengukur ini dapat pula digunakan untuk mengukur
jari-jari atau dalam dari sebuah tabung.
Sebelum menggunakan alat pengukur ini sebaiknya diteliti terlebih dahulu apakah
alat tersebut mempunyai kesalahan titik nol. Gambar alat jangka sorong ini dapat dilihat
seperti Gambar 1.
Gambar 1. Alat ukur Jangka Sorong
Kesalahan titik nol ini dapat dibaca bila A dan B diimpitkan ternyata titik nol
yang terdapat pada skala tambahan (nonius) tidak tepat berimpit dengan titik nol yang
terdapat pada skala dasar F, sedangkan untuk kesalahan pada titik nol bila keadaan
sebaliknya. Misalkan dalam pengukuran suatu benda skala dasar menunjukkan 1,49 cm,
sedangkan kesalahan titik nolnya –0,07 cm, maka jarak antara paruh A dan B adalah (
1,49 + 0,07 = 1,56 ) cm.
CARA PENGGUNAAN JANGKA SORONG
Bila mengukur garis tengah suatu tabung, letakkanlah tabung A dan B sehingga
tebal tabung tepat diantara paruh A dan B, dengan demikian dapat dibaca pembagian
skala beberapa jarak antara paruh A dan B ini.

Jika jarak tidak tepat barulah bilangan bulat dalam nilai meter dibaca dalam skala
dasar, dengan nonius dapat dibaca pembagian skala telih teliti. Panjang skala pada nonius
9 mm dibagi menjadi 10 skala yang sama, jadi jarak dua garis kecil yang ada pada nonius
sebesar 0,09 cm.
Dalam suatu pengukuran (lihat Gambar 2) pada waktu paruh A dan B berimpit,
skala nol nonius terletak berimpit dengan skala nol, jadi berarti pada keadaan ini tidak
mempunyai kesalahan titik nol (Gambar 2a). Setelah benda yang hendak diukur
diletakkan diantara paruh A dan B ternyata titik nol nonius terletak diantara 8 dan 9 pada
skala dasar F (Gambar 2b).
Gambar 2. Keadaan titik nol Alat Jangka Sorong
Kemudian lihat garis manakah pada nonius yang berimpit dengan garis skala
dasar. Pada gambar diatas terlihat bahwa pada garis ke-6 nonius berimpit pada salah satu
pada skala dasar (disisi pada skala 14), jadi tebal benda tersebut adalah 8 mm + 0,6 mm
atau 8,6 mm, atau dapat juga dihitung demikian, garis ke-6 pada nonius berimpit pada
garis nol 14 pada skala dasar. Jadi jarak AB adalah 14-6x0,9 = 8,6 mm atau 8+0,6 = 8,6
mm.
PERHATIAN … !!!
Pada waktu pengukuran suatu benda agar jarak AB tidak berubah, sekrup R diatas
nonius diputar keras, bila terdapat kesalahan titik nol, pengukuran diatas harus dikurangi
atau ditambah dengan kesalahan titik nolnya. Untuk mengukur garis tegak tabung dapat
dipakai paruh CD yang terletak diatas paruh AB (lihat Gambar 1), sedang batang E
digunakan untuk mengukur dalamnya tabung.

Pada waktu mengadakan pengukuran terhadap suatu benda, maka supaya jarak
AB tidak berubah hendaknya sekrup R diatas nonius diputar hingga keras. Jika terdapat
kesalahan titik nolnya, untuk mengukur garis tengah dari tabung dalam dapat dipakai
paruh CD yang berada diatas paruh A dan B (lihat Gambar 1), sedangkan batang E
digunakan untuk mengukur dalam tabung.
MIKROMETER SEKRUP
Alat lain untuk mengukur jarak yang sangat kecil dengan teliti adalah Mikrometer
Sekrup. Gambar alat mikrometer sekrup ini dapat dilihat seperti Gambar 3.
Gambar 3. Alat ukur Mikrometer Sekrup
Kalau sekrup D diputar, maka ujung B dapat bergeser mundur atau maju. Jika sekrup D
diputar satu putaran, jarak AB bergeser sejauh 0,5 mm. Disekeliling dari kiri C diberi
skala (yang merupakan nonius S) dan banyaknya skala 50 buah.
Pada sekrup D diberi skala yang melingkar dan sejajar dengan nonius C serta
mempunyai ukuran dan banyak skala sama dengan nonius C dan juga pada batang dasar
E ini terdapat skala yang memanjang yang merupakan skala dasar E.
CARA PENGGUNAAN MIKROMETER SEKRUP
Sebelum digunakan untuk mengukur benda, tentukan terlebih dahulu kesalahan
titik nolnya, apakah pada waktu ujung A dan B berimpit (jangan dipaksa waktu
menghimpitkannya), titik nol pada nonius C berimpit atau tidak pada titik nol nonius D.
Jika berimpit berarti tidak mempunyai kesalahan titik nol, jika mempunyai kesalahan
titik nol positif dan sebaliknya mempunyai kesalahan titik nol negatif.
Jika titik nol nonius C berimpit dengan skala 48 nonius D, berarti mempunyai
kesalahan titik nol negatif sebanyak 2 skala. Tetapi jika titik nol nonius C berimpit
dengan skala 2 nonius D berarti mempunyai kesalahan titik nol positif sebanyak 5 skala.

Andai kata akan mengukur garis tengah sesuatu kawat dan pengukuran ini digunakan
mikrometer sekrup yang mempunyai kesalahan titik nol berbeda. Digunakan micrometer
sekrup X dengan kesalahan titik nol negatif dan micrometer sekrup Y dengan kesalahan
titik nol positif.
Jika kawat itu waktu diukur dengan micrometer sekrup X mempunyai dua
perputaran ditambah dengan 19 skala pada nonius D, dari data-data diatas kita dapat
membuat perhitungan sebagai berikut :
Mikrometer Sekrup X Mikrometer Sekrup Y
Jumlah skala pada nonius C 50 50
Jarak skala pada tiap-tiap Skala
nonius C mm
50
5,0
mm
50
5,0
Tabel dari kawat yang terbaca
Mikrometer Sekrup
2 putaran +
19 skala nonius C
2 putaran +
26 skala nonius D
Kesalahan titik nol Kurang 2 skala
Pada nonius D
Lebih 5 skala
Pada nonius D
Skala yang besarnya dipakai Oleh
micrometer sekrup
2 putaran +
21 skala nonius D
2 putaran +
21 skala nonius D
Garis tengah kawat 0,121 cm 0,121 cm
Pada percobaan mencari kelengkungan batang logam akan dijumpai suatu alat pengukur
lengkung yang kerjanya hampir menyerupai sekrup.

TEORI KETIDAKPASTIAN PENGUKURAN DALAM PERCOBAAN
I. PENDAHULUAN
Pada percobaan Fisika hasil yang diperoleh biasanya tidak dapat langsung
diterima karena harus dipertanggungjawabkan keberhasilan dan kebenarannya.
Hal ini disebabkan oleh kemampuan manusia yang terbatas dan ketelitian alat-alat
yang digunakan serta mempunyai batas kemampuan tertentu. Dengan kata lain peralatan
dan sarana (termasuk waktu) yang tersedia bagi kita membatasi tujuan dan hasil yang
dapat dicapai.
Hasil percobaan baru dapat diterima apabila harga besaran yang diukur
dilengkapi dengan batas-batas penyimpangan dari hasil tersebut, yang disebut sesatan
(ketidakpastian). Jika hasil tersebut diketahui penyimpangan terlalu besar maka bila
diperlukan percobaan harus diulang kembali dengan berbagai cara misalnya :
Mengulang pengukuran beberapa kali yang lebih teliti atau mengganti alat-alat
percobaan dengan alat yang lebih baik ketelitiannya. Jadi jelaslah untuk keperluan ini
mutlak diperlukan teori sesatan (ketidakpastian). Dengan demikian dapat ditentukan
sesatan pada hasil percobaan agar dapat memberi penilaian yang baik.
II. KETIDAKPASTIAN PADA PENGUKURAN
Kesalahan atau Error dalam suatu percobaan dapat dibagi atau dua golongan yaitu
:
II.1. Kesalahan Bersistem (Systematic Error)
Kesalahan yang bersumber pada alat pengukuran yang dipakai besarannya,
kesalahan biasanya konstant sehingga sering sekali dinamakan sebagai kesalahan konstan
(Constant Error).
Kesalahan Bersistem ini dapat terjadi karena :
a. Kesalahan titik nol (Zero Error).
b. Kesalahan pada kalibrasi pengukuran.
c. Kesalahan orangnya (pengamat), kesalahan ini disebabkan oleh kebiasaan
seorang pengamat. Misalnya seorang pengamat sering kali membuat
kesalahan karena kedudukan matanya terlalu rendah atau terlalu tinggi
sewaktu membaca tinggi kolam air didalam pipa yang tegak. Kesalahan ini
disebut : Parallak.

d. Terjadinya gesekan dan fatiqua (kesalahan) pada alat karena sering dipakai.
e. Kondisi percobaan, jika sebuah alat digunakan dengan kondisi percobaan
yang berbeda dengan kondisi sewaktu kalibrasi, akan menghasilkan
kesalahan.
f. Gangguan teknis : misalnya pada waktu pengukuran terjadi gangguan seperti
adanya kebocoran-kebocoran yang akan mengganggu system dan
menyebabkan kesalahan.
II.2. Kesalahan Random
Karena pengulangan pengukuran selalu memberikan hasil yang berbeda-beda,
maka harga tersebut juga akan berbeda dengan harga yang sebenarnya. Kesalahan ini
dinamakan kesalahan Random atau kesalahan kebetulan, yang terjadi atas :
a. Kesalahan penafsiran, kebanyakan alat pengukuran memerlukan suatu penafsiran
pada bagian skala tertentu dan penafsiran ini dapat berubah dari waktu kewaktu yang
lain.
b. Keadaan penyimpangan, seperti suhu, tekanan udara, atau tegangan listrik.
c. Gangguan, misalnya : adanya getaran mekanis atau pengaruh putaran motor dari alat
listrik.
d. Definisi, walaupun proses pengukuran telah sempurna, pengulangan pengukuran
yang sama selalu akan memberikan penyimpangan, besaran yang diamati tidak
didefinisikan secara tetap.
Misalnya :
Panjang suatu meja persegi bukanlah suatu besaran yang terdefinisi secara eksak. Hal
ini disebabkan bahwa kalau kita teliti, sisi meja tidaklah rata ataupun mungkin tidak
tepat sejajar.
Sehingga walaupun kita menggunakan alat ukur yang sangat baik untuk mengukur
meja tersebut, harga yang diperolah selalu berubah-ubah tergantung penampang
panjang yang kita ukur.
II.3. Kesalahan-Kesalahan Lain
Kesalahan lain yang tidak termasuk bahasan 1 dan 2 yang perlu diperhatikan
adalah :

a. Kekeliruan membaca alat atau skala alat dan mengatur kondisi percobaan. Kesalahan
ini dapat diatasi dengan cara melakukan percobaan seteliti mungkin atau bila
memungkinkan mengulangi percobaan tersebut.
b. Kesalahan perhitungan, yaitu kesalahan memasukkan harga atau angka-angka
perhitungan, menggunakan kalkulator, menggunakan daftar logaritma dan
sebagainya.
III. PERHITUNGAN KESALAHAN
III.1. Sesatan Taksiran
Bila pengukuran dilakukan hanya satu kali biasanya sesatan diambil setengah kali
skala terkecil dari alat ukur yang digunakan.
Contoh :
Menggunakan mistar yang skala terkecil 1 mm, bila tebal plat diukur menghasilkan 50
mm, maka hasilnya dapat ditulis :
t = ( 50  0,5 ) mm atau
= ( 5,0  0,05 ) x 10 mm
t = 0,5 adalah sesatan mutlak (absolut), sedangkan sesatan relatifnya dapat dinyatakan
dengan :
= %100x
t
t
= %100
50
5,0
x
= 1 %
III.2. Menentukan Harga Rata-rata (nilai terbaik) dan Sesatannya
Misalkan kita melakukan N kali pengukuran didapat hasil sebagai berikut :
X1, X2, X3, ……… , XN
Untuk mendapatkan nilai yang terbaik (benar) dari pengukuran tersebut adalah merata-
ratakan hasil pengukuran tersebut, yaitu :
N
X
N
XXXX
X
NN
N



...321
(III.2.1)
( NX = rata-rata = nilai terbaik), maka simpangan atau deviasi untuk :

X1 adalah X1 = X1 - X
X2 adalah X2 = X2 - X
XN adalah XN = XN - X 
Harga sesatan rata-rata adalah :
N
XXXXXXXX
X
N 

...321
N
XX
XX
N 
 (III.2.2)
Persamaan (III.2.2) ini disebut deviasi rata-rata.
Sedangkan deviasi standar atau simpangan baku semesta X(x) : didefinisikan sebagai :
xx V
Dimana Vx adalah variasi yang didefinisikan
N
XX
V NN
x
)(
2
 

dengan N menuju tak hingga.
Sehingga x dapat dituliskan :
N
XX
V
NN
xx
)(
2

 (III.2.3)
dengan N menuju tak hingga.
Harga x berada pada pengukuran tak terhingga yang tidak mungkin dilakukan dengan
menggunakan suatu pendekatan teori samping x dapat diganti dengan SN yang
dinamakan simpangan baku contoh (sample standard deviation). N memberikan
gambaran tentang simpangan X terhadap Xo.
Sedangkan SN menggambarkan simpangan X terhadap NX maka :
)1(
)(
2



N
XX
S N
N
yang dapat diubah menjadi,
)1(
)(
22



N
XNX
S N
N (III.2.4)
Dimana N  8 (untuk N = 1  SN tidak mempunyai arti).

Menurut teori percobaan SN sebenarnya adalah NX
S yaitu ketidakpastian pada nilai rata-
rata contoh XN yang mempunyai harga
N
S
S N
X N
 (III.2.5)
Penggantian SN menjadi SX hal ini disebabkan kurva sebaran nilai rata-rata contoh X
lebih sempit dari pada kurva sebaran pengukuran tunggal (X1) berarti Xx  yaitu
kita mengulangi pengukuran N kali dengan hasil rata-rata, misalnya 1X maka ada
kepastian 66% 1X terletak dalam selang XX N  didalam praktek percobaan tak
terhingga, tak mungkin kita lakukan, jadi X dan X
 tidak dapat diketahui dan sebagai
pengganti terbaik dipakai SN dan NX
S seperti diatas.
Untuk pemakaian selanjutnya digunakan,
)1(
22




NN
XNX
N
S
SX
NNN
X N
(III.2.6)
dengan N  8.
Apabila X diukur N kali, ada kemungkinan 68% bahwa simpangan nilai rata-rata contoh
X terhadap nilai benar Xo tidak lebih dari NX
S dengan kata lain “ada jaminan 68%
bahwa Xo ada dalam interval NX
SX  ” dengan demikian persoalan selesai.
Kita tidak dapat mengetahui nilai benar Xo dari eksperimen, tetapi dengan mengadakan
pengulangan cukup banyak, kita dapat menyodorkan sebagai penggantinya nilai contoh
X dan dapat memberikan pernyataan sampai berapa jauh X menyimpang dari Xo.
Contoh :
X = 10,0; 10,2; 10,0; 10,0; 9,8; 10,1; 9,8; 10,3; 9,8; 10,0
Maka nilai terbaik X dan sesatannya ( X  X) dapat dicari sebagai berikut :
N XN 2
NX
1 10,0 100,00
2 10,2 104,04
3 10,0 100,00
4 10,0 100,00
5 9,8 96,04
6 10,1 102,01
7 9,8 96,04
8 10,3 106,09

9 9,8 96,04
10 10,0 100,00
 XN = 100,0  2
NX = 1000,26
0,10
10
0,100


N
X
X
N
N
0,100)0,10()( 22
NX
)1(
22




NN
XNX
SX
NN
X N
)110(10
0,1001026,1000



 x
05,0
90
26,0

maka nilai terbaik X = ( 10,00  0,05 )
III.3. Contoh Perhitungan
III.3.1. Ketelitian Pengukuran
Suatu amperemater mempunyai skala 0 – 5 A, dengan pembagian skala terkecil
0,1 A.
(a). Berapa ketelitian alat itu bila skala pada pengukuran, skala penuh ?
(b). Dan pada setengah skala ?
Jawab :
(a). I = ½ skala terkecil = ½ x 0,1 A, dan I = 5 A
Ketelitian %1%100
5
05,0


x
I
I
(b). I = ½ skala terkecil = ½ x 0,1 A = 0,05 A, dan I = 2,5 A
Ketelitian %2%100
5,2
05,0


x
I
I
III.3.2. Sesatan Yang Ditentukan Oleh Skala Alat
1. Tahanan sepotong kawat ditentukan menurut hokum ohm.
Hasilnya adalah V = ( 1,0  0,05 ) volt dan I = ( 5,0  0,05 ) mA atau I = ( 5,0  0,05
) x 10-3
A.

Berapakah  R ?
Jawab :
ohm
xI
V
R 200
100,5
0,1
3
 
I
I
V
V
R
R 




5
05,0
0,1
05,0
200

R
ohmxR 12200)01,005,0( 
Jadi R = ( 200  12 ) ohm
2. Pada percobaan tegangan permukaan air digunakan rumus :
rg
h

2

Bila : r = ( 0,30  0,005 ) mm
g = ( 980  2% ) cm/det2
 = 1,0 g/cm3
dan h = ( 50,0  0,05 ) mm
Tentukan :  dan 
Jawab :
rg
h

2
 
2
30,09800,10,50
2
xxxrgh



50,73
r
r
g
g
h
h 








(tidak mempunyai sesatan)
0018,0
30,0
005,0
980
02,0
50
05,0
50,73


13,050,730018,0  x
Jadi )13,050,73(  dyne.
3. Sesatan yang paling mempengaruhi
Rumus lensa tipis (Gauss) :
'
'
SS
SS
f


Bila S = ( 8,0  0,05 ) cm dan S’ = ( 24,0  0,05 ) cm

Berapakah ( f  f ) ?
Jawab:
'
'
SS
SS
f

 
'
111
SSf

0,24
1
0,8
11

f
0,6f cm
'
'
S
S
S
S
f
f 




008678,0
)0,24(
05,0
)0,8(
05,0
)0,6( 222

f
0312,0)0,6(008678,0 2
 xf
Jadi )03,000,6( f cm.

I. GERAK JATUH BEBAS
1.1. TUJUAN PERCOBAAN
► Dapat memahami dan menentukan percepatan benda pada gerak jatuh bebas.
1.2. ALAT DAN BAHAN BESERTA FUNGSINYA
1. Dasar Statif, A
........................................................................................................................................
2. Batang Statif
........................................................................................................................................
3. Magnet pemegang bola logam
........................................................................................................................................
4. Gerbang cahaya
........................................................................................................................................
5. Bola logam
........................................................................................................................................
6. Timer counter, AT-01
........................................................................................................................................
7. Bosshead, universal
........................................................................................................................................
8. Rol meter, 3m
........................................................................................................................................
9. Kabel penghubung
........................................................................................................................................
10. Plumb bob
........................................................................................................................................

1.3. DASAR TEORI
Alat percobaan gerak jatuh bebas didesain untuk membantu mahasiswa
memahami gerak jatuh bebas, yaitu pengukuran waktu jatuh bola logam, memeriksa
hubungan ketinggian dan waktu tempuh, dan mengukur percepatan gravitasi g.
Dengan menggunakan pencacah waktu (Timer counter AT-01) memungkinkan
pengukuran waktu jatuh bebas sampai skala millisekon. Waktu jatuh bebas diukur
menggunakan dua sensor gerbang cahaya. Pada saat bola dilepaskan, Timer counter
secara otomatis segera memulai melakukan pengukuran waktu, timer counter akan
membaca waktu tempuh bola dari magnet pemegang bola ke masing-masing gerbang
cahaya infra merah pada gerbang cahaya kedua, timer counter otomatis akan
menghentikan pengukuran.
Tinjauan Teori:
Persamaan kinematika gerak untuk gerak benda dengan percepatan tetap a,
diberikan oleh:
21
12ox v t at  (1)
sehingga untuk sebuah benda jatuh bebas dengan percepatan adalah g (g adalah
percepatan gravitasi) dan kecepatan awal adalah nol (vo = 0) didapatkan persamaan:
21
2h g t (2)
t adalah waktu yang diperlukan benda jatuh dari ketinggian h. Jika persamaan 2
digunakan untuk gerbang cahaya 1 dan gerbang cahaya 2 (Gambar 1) berikut

Gambar 1. Skema Percobaan
maka diperoleh dua persamaan yang memberikan hubungan antara ketinggian dan waktu
tempuh yang diperlukan oleh suatu benda ke masing-masing gerbang cahaya. Persamaan
untuk masing-masing ketinggian diberikan oleh:
21
1 12h g t untuk gerbang cahaya 1 (3)
21
2 22h g t untuk gerbang cahaya 2 (4)
Dari persamaan 3 dan persamaan 4 dapat dilihat bahwa percepatan jatuh bebas pada
masing-masing ketinggian adalah sama dengan g.
Dengan mengurangkan persamaan 4 dengan pesamaan 3, maka dapat diperoleh
besaran percepatan gravitasi g, yaitu
2 1
2 2
2 1
2( )
( )
h h
g
t t


 (5)
Persamaan 5 di atas akan digunakan untuk menentukan besar percepatan jatuh bebas dan
memverifikasi bahwa percepatan pada gerak jatuh bebas adalah sama dengan percepatan
garvitasi.
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1.4. PROSEDUR PERCOBAAN
II. RANGKAIAN PERALATAN
1. Rangkai peralatan seperti pada Gambar 2. Pasang magnet pemegang bola pada
bagian atas statif, gerbang cahaya pertama di tengah batang, dan gerbang cahaya
kedua pada bagian paling bawah.
Gambar 2. Rangkaian Percobaan
2. Hubungkan magnet pemegang bola ke keluaran P1/E.MAGNET pada Timer
counter AT-01 menggunakan kabel penghubung.
3. Hubungkan gerbang cahaya satu dan gerbang cahaya dua secara berurutan pada
terminal P1 dan P2 pada Timer counter. Atur jarak kedua gerbang cahaya
sedemikian rupa sehingga jarak antara keduanya adalah 10 cm.
4. Hubungkan Timer counter AT-011ke soket jala listrik. Timer counter dalam kead
an mati (OFF).

5. Hidupkan Timer counter AT-01. Tekan tombol pemilih fungsi pada timer counter
beberapa kali sedemikian rupa sehingga timer berada pada fungsi Gravity
Acceleration. Pada keadaan tersebut lampu LED pada fungsi tersebut dan pada
fungsi E.MAGNET akan menyala. LED pada fungsi E.MAGNET menunjukkan
bahwa sumber tegangan untuk magnet pemegang bola juga dalam keadaan hidup
(ON).
6. Atur kelurusan magnet pemegang bola, dan kedua gerbang cahaya sedemikian
rupa sehingga trayektori bola logam dari magnet pemegang bola menghalangi
berkas cahaya pada masing-masing gerbang cahaya. Untuk memudahkan
mengatur kelurusan, gunakan plumb bob.
II. PELAKSANAAN PENGAMBILAN DATA
1. Hidupkan Timer counter AT-01.
2. Tekan tombol FUNCTION pada Timer counter AT-01 sedemikian rupa beberapa
kali sehinggga pewaktu berada pada fungsi Gravity Acceleration. Timer counter
berada pada fungsi Gravity Acceleration ditunjukkan oleh nyala merah lampu
indicator LED. Pada keadaan ini, Timer counter juga akan menyalakan fungsi
E.MAGNET yang ditunjukkan oleh nyala merah indicator LED. Dengan
menghubungkan terminal E.MAGNET ke magnet pemegang bola logam
menggunakan kabel penghubung, maka pada kumparan magnet pemegang akan
timbul medan magnet sehingga dapat menarik benda-benda konduktor.
3. Pasang bola logam pada magnet pemegang bola logam. Mulailah melakukan
pengukuran dengan cara menekan tombol E.MAGNET pada Timer counter.
Setelah tombol E.MAGNET ditekan, maka fungsi E.MAGNET akan mati
sehingga medan magnet pada magnet pemegang bola juga akan hilang. Bola
logam akan jatuh melewati gerbang cahaya 1 dan gerbang cahaya 2 secara
berurutan.
4. Baca hasil pengukuran waktu pada Timer counter AT-01. Timer akan
menampilkan waktu tempuh bola ke gerbang cahaya 1 dan gerbang cahaya 2
secara berurutan. Catat hasil pengukuran waktu ini ke dalam Tabel Pengamatan.
5. Ubah ketinggian jatuh bebas bola h. Atur ulang Timer dengan menekan tombol
FUNCTION satu kali sedemikian rupa sehingga fungsi E.MAGNET kembali

aktif (ON) kembali. Ulangi langkah percobaan 1 s/d 4 untuk beberapa ketinggian
yang berbeda dengan menekan tombol E.MAGNET.
1.5. TUGAS PENDAHULUAN
1. Buktikan rumus 2v gh !
2. Jelaskan ketiga hukum Newton baik secara teoritis maupun matematis!
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1.6. DATA HASIL PENGAMATAN
Tabel Hasil Pengamatan
No
Massa
Peluru
(gram)
h1 (cm) h2 (cm)
Waktu t1
(ms)
Waktu t2
(ms)
1 10 30
2 10 50

1.7. PENGOLAHAN DATA
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1.8. ANALISA
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1.9. TUGAS AKHIR
1. Hitung besarnya percepatan gerak jatuh bebas peluru tersebut menggunakan
persamaan (3), periksa hasilnya apakah besar percepatan jatuh bebas peluru
memiliki harga yang sama atau harga yang berbeda pada ketinggian jatuh yang
berbeda? Jelaskan jawaban Anda!
2. Berdasarkan pada hasil percobaan, benarkan dugaan prediksi teori bahwa
percepatan jatuh bebas sama dengan percepatan gravitasi? Jelaskan jawaban
Anda!
3. Analisa hasil percobaan dan perhitungan yang anda lakukan.
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1.10. KESIMPULAN
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LAMPIRAN GAMBAR

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 BESERTA FUNGSINYA
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 ...................................................................... (2.1)
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 ..................................................................... (2.2)

Keuntungan mekanis dengan menggunakan katrol bergerak adalah perbandingan antara
besar gaya beban FB dan gaya kuasa Fk.
Keuntungan Mekanis = FB / Fk = 2 ............................ (2.4)
Jelas bahwa untuk mengangkat suatu benda dengan satu katrol bergerak, cukup
mengerjakan ½ 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 ............................ (2.6)
Sehingga untuk mengangkat benda sistem katrol 4c cukup menggunakan ½ 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.
2.5. TUGAS PENDAHULUAN
1. Sebutkan kegunaan katrol pada kehidupan kita.
2. Mengapa dalam mengangkat beban yang berat orang sering menggunakan katrol.
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2.6. TABEL HASIL PENGAMATAN
A. Massa Beban
Tabel 1. Tanpa Katrol Tabel 2. Katrol Tetap
No.
Massa Beban (kg)
No.
Massa Beban (kg)
I II III I II III
1. 1.
2. 2.
3. 3.
4. 4.
5. 5.
Tabel 3. Katrol Bergerak Tabel 4. Katrol Ganda
No.
Massa Beban (kg)
No.
Massa Beban (kg)
I II III I II III
1. 1.
2. 2.
3. 3.
4. 4.
5. 5.
Tabel 5. Katrol Majemuk
No.
Massa Beban (kg)
I II III
1.
2.
3.
4.
5.

B. Gaya
Tabel 1. Tanpa Katrol Tabel 2. Katrol Tetap
No.
Gaya (N)
No.
Gaya (N)
I II III I II III
1. 1.
2. 2.
3. 3.
4. 4.
5. 5.
Tabel 3. Katrol Bergerak Tabel 4. Katrol Ganda
No.
Gaya (N)
No.
Gaya (N)
I II III I II III
1. 1.
2. 2.
3. 3.
4. 4.
5. 5.
Tabel 5. Katrol Majemuk
No.
Gaya (N)
I II III
1.
2.
3.
4.
5.

2.7. PENGOLAHAN DATA
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