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                             Batasan materi asas ganjil 2024-2025

 

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Praktik Getaran dan Gelombang

 Tujuan Percobaan

• Menjelaskan pengertian getaran menggunakan contoh bandul sederhana.
• Melakukan percobaan untuk mengukur periode getaran bandul.
• Menghitung periode (T) dan frekuensi (f) getaran dari data pengamatan.
• Menyimpulkan hubungan antara panjang tali bandul dengan periode getaran.

 Dasar Teori

Getaran adalah gerakan bolak-balik suatu benda melalui posisi keseimbangan. Salah satu contoh benda yang dapat menunjukkan getaran adalah bandul sederhana, yaitu alat yang terdiri dari seutas tali dan sebuah beban di ujungnya. Ketika bandul ditarik ke samping lalu dilepas, bandul akan bergerak dari kiri ke kanan dan kembali lagi, sehingga membentuk gerakan berulang yang disebut getaran. Satu getaran bandul terjadi ketika bandul bergerak dari titik awal ke sisi lain dan kembali ke titik awal tersebut. Untuk mengetahui karakteristik getaran, ada dua besaran penting yang harus dihitung, yaitu periode dan frekuensi. Periode (T) adalah waktu yang diperlukan bandul untuk melakukan satu getaran penuh dan dapat dihitung dengan membagi waktu total dengan jumlah getaran. Misalnya, jika bandul bergetar 20 kali dalam 40 detik, maka periodenya adalah 2 detik. Besaran kedua adalah frekuensi (f), yaitu jumlah getaran setiap detik, yang merupakan kebalikan dari periode. Jika periode bandul 2 detik, maka frekuensinya adalah 0,5 Hz. Dalam kondisi amplitudo kecil, periode bandul dipengaruhi oleh panjang tali dan percepatan gravitasi bumi, namun tidak dipengaruhi oleh besar beban bandul. 
Prinsip getaran pada bandul sangat mudah ditemukan dalam kehidupan sehari-hari, misalnya pada ayunan di taman bermain atau pada jam bandul tradisional yang memanfaatkan getaran teratur untuk mengukur waktu. 

Alat & Bahan 

 

Prosedur Kerja

1.Buat bandul dengan mengikatkan beban pada ujung tali.
2.Gantungkan bandul pada penyangga yang kokoh dengan panjang sekitar 15 cm
3.Ukur panjang tali dari titik gantung sampai tengah beban, catat sebagai panjang bandul.
4.Tarik bandul sekitar 30 derajat ke samping (amplitudo kecil).
5.Lepaskan bandul tanpa memberi dorongan tambahan.
6.Hitung waktu untuk 20 getaran menggunakan stopwatch.
7.Catat hasil pengamatan pada tabel.
8.Ulangi percobaan dengan panjang tali 30 cm
9.Hitung periode dan frekuensi untuk setiap panjang tali. 

 

 

 

Refleksi

1. Bagaimana hubungan antara panjang tali dengan periode getaran?
2. Apakah massa bandul mempengaruhi periode getaran? Jelaskan berdasarkan teori.
3. Mengapa frekuensi menjadi lebih kecil ketika periode semakin besar?
4. Mengapa pengukuran dilakukan untuk banyak getaran (misalnya 20 getaran), bukan hanya satu getaran? 

 

 

 

 Sumber : LKPD Praktik Getaran dan Gelombang oleh M. Masyhuri Wijaya, S.Pd (Laboran SMP ISLAM ATHIRAH BUKIT BARUGA)  

BATASAN MATERI ASAS GANJIL 2024-2025

 I. PENGENALAN SEL DAN MIKROSKOP / Cell Structure and Function (english class) 

• mikroskop, bagian-bagian dan fungsinya
• sel, komposisi penyusun sel dan fungsinya
• perbedaan sel hewan dan tumbuhan

 II. STRUKTUR DAN FUNGSI TUBUH MAKHLUK HIDUP 

• Nutrisi dan pencernaan makanan / Nutrition and the Human Digestive System (english class) 
•  Organ-organ pada sistem pencernaan makanan dan fungsinya 
•  Sistem peredaran darah manusia  / Human Circulatory System (english class)
• Sistem pernapasan manusia (mekanisme pernapasan manusia) /  Human Respiratory System (english class)  
• Sistem ekskresi manusia / Human Excretory System (english class)  : 
• Organ-organ pada sistem ekskresi manusia, bagian, dan fungsinya

III. USAHA, ENERGI, DAN PESAWAT SEDERHANA / Energy, Work and Simple machine (english class) 

• Konsep hubungan usaha dan energi
• Kekekalan energi mekanik
• Penerapan konsep pesawat sederhana (tuas, katrol, bidang miring) dalam kehidupan.

IV. GETARAN DAN GELOMBANG /   VIBRATIONS AND WAVES (English class)

• analisis hubungan besaran-besaran (amplitudo,jumlah getaran, frekuensi, periode) pada getaran bandul matematis.
• analisis hubungan besaran-besaran (amplitudo,jumlah getaran, frekuensi, periode, cepat rambat gelombang) pada gelombang transversal dan longitudinal

 SOAL - SOAL ASTS DAN ASAS 2021 - 2024 dan TUGAS GANJIL 2024/2025

 

 

Vibrations and Waves

 What is Vibration?

A vibration is a back-and-forth motion of an object around a fixed point or
A periodic disturbance or motion about a fixed position.
In simple terms, it is a repeated movement that happens over and over again. 

 Example:

• The movement of a pendulum.
• The strings of a guitar when plucked.
• The diaphragm of a speaker when it produces sound.
• a swing moving back and forth.

Properties of Vibration and Important Terms in Vibration

 

• One complete vibration (oscillation): when an object moves from the starting point, goes to the farthest point, returns, and repeats the same motion.
• Equilibrium Position:The point where the object experiences no net force.
• Amplitude:The maximum displacement of the object from its equilibrium position.
• Period:The time taken for one complete cycle of oscillation.
• Frequency:The number of oscillations per unit time.
• Restoring Force:The force that pulls the object back towards its equilibrium position.

Parameters of Vibration

• Amplitude (A):Maximum displacement of the vibrating object from its equilibrium position. (Unit: meter)
• Period (T):Time taken for one complete cycle of vibration. (Unit: second)
• Frequency (f):Number of vibrations per unit time. (Unit: Hertz (Hz)) 

 The Pendulum

A pendulum is a simple device that swings back and forth freely under the influence of gravity.
It usually consists of a weight (called a bob) attached to the end of a string or rod that is fixed at one point.

Examples of pendulums:

• The swinging pendulum in a wall clock.
• A swing in a playground.
• A science experiment using a small ball and string.

Parts of a Pendulum

 

 

1. Bob → the weight at the end of the string.

2. String or Rod → holds the bob and allows it to swing.

3. Fixed Point → the point where the string is attached, allowing the pendulum to move freely.

4. Equilibrium Position → the central position where the pendulum naturally rests.

 

How a Pendulum Works

When the pendulum is pulled to one side and released, it swings because of gravity.

• At the highest point, the pendulum has maximum potential energy.

• As it moves down, this energy changes into kinetic energy (energy of motion).

• At the lowest point, the pendulum has maximum speed.

• Then it moves up to the other side, repeating the motion.

This repeated motion is called a vibration or oscillation.

  Formula:

 

 

where


f = frequency (Hz)
T = period (s)
n = One complete vibration (oscillation)
t = time (s) 

 

 Exercises

Short Answer Questions 

1. What is meant by one complete vibration (oscillation)? 
2. What is the definition of frequency?
3. Write the formula for calculating frequency. 

Essay Questions 

1. Explain what a vibration is and give two real-life examples that show vibration in daily life.
2. Describe one complete vibration (oscillation). Use your own words and include a simple illustration if needed.
3. Explain the difference between period and frequency. How are they related to each other?
4. A pendulum is pulled to one side and released. Describe step-by-step what happens to the pendulum during one full vibration.
5.  A pendulum completes 40 vibrations in 20 seconds. Calculate the frequency and the period of the pendulum. Explain your steps clearly.

 

WAVES

A wave is a disturbance that transfers energy from one place to another without moving matter permanently.

Waves can travel through solids, liquids, gases, or even empty space (for certain types of waves).

Examples of waves:

• Water waves

• Sound waves

• Light waves

• Waves on a rope

 

Types of Waves

 

A. Based on the Direction of Vibration

1) Transverse Waves

• The vibration of particles is perpendicular (up and down) to the direction the wave travels.

• Has crests (highest points) and troughs (lowest points).

Examples:

• Waves on a rope

• Water waves

• Light waves

2) Longitudinal Waves

• The vibration of particles is parallel (back and forth) to the direction the wave travels.

• Has compressions (particles close together) and rarefactions (particles spread apart).

Example:

• Sound waves

Parts of a Wave

Transverse Wave Parts:

 

• Crest: highest point of a wave

• Trough: lowest point

• Wavelength (λ): distance between two crests or two troughs

• Amplitude: height of the wave from the middle to the crest or trough

   

Longitudinal Wave Parts:

 

• Compression: area where particles are close

• Rarefaction: area where particles are spread out

• Wavelength: distance between two compressions or two rarefactions

 

 

source : https://byjus.com/physics/difference-between-longitudinal-and-transverse-wave/ 

 

Wave Characteristics

1) Frequency (f)

• Number of waves or vibrations produced per second.

• Measured in Hertz (Hz).

2) Period (T)

• Time needed to complete one wave or one vibration.

• Measured in seconds (s).

Formula:

$$f = \frac{1}{T} \quad \text{and} \quad T = \frac{1}{f}$$

3) Wave Speed (v)

• The speed at which a wave travels.

Formula:

$$v=f\times \lambda$$

Where:
$v$ = wave speed (m/s)
$f$ = frequency (Hz)
$or lambda$ = wavelength (m)

 

B. Types of Waves Based on the Medium

Waves can be classified into two types based on whether they need a medium to travel:

 1. Mechanical Waves

Mechanical waves require a medium (such as air, water, or solids) to travel.

They cannot travel through a vacuum (empty space).

Examples:

• Sound waves
• Water waves
• Waves on a rope or spring
• Earthquake waves (seismic waves)

Particles of the medium vibrate to transfer energy. They can be transverse or longitudinal waves.

---

2. Electromagnetic Waves

Electromagnetic waves do NOT need a medium. They can travel through empty space (vacuum).

Examples:

• Light

• Radio waves

• Microwaves

• X-rays

• Gamma rays

Made of oscillating electric and magnetic fields. All electromagnetic waves travel at the speed of light in a vacuum (≈ 3 × 10⁸ m/s). 

 Exercises

Essay Questions

1. A water wave has a frequency of 5 Hz and a wavelength of 0.8 meters. Calculate the speed of the wave and explain each step of your calculation. 
2. A rope wave travels with a speed of 12 m/s and its frequency is 3 Hz. Find the wavelength of the wave. Show your work clearly. 
3. A student creates waves in a spring. The waves move at 2 m/s, and one wave takes 0.25 seconds to pass a point. Calculate the frequency and wavelength of the wave. Write the formula and the steps. 
4. A wave completes 60 vibrations in 15 seconds. Calculate the frequency and the period of the wave. Explain how frequency and period are related.
5. 24 water waves pass a point in 6 seconds. What is the frequency of the waves? 
6.  How many wavelenght of this longitudinal picture below :

  

    7. The questions below refer to this diagram :

 

 

(a) Calculate the wavelength of the waves shown.

(b) What is the amplitude of these waves?

 

    8. A wave of wavelength 2 m travels 60 m in 12 seconds.

 

(a) What is the speed of the wave?

(b) How many waves would be produced in 12 seconds?

(c) What is the frequency of the wave?

  

9.  The questions below refer to this diagram : The waves travels in 5 seconds. Calculate the frequency and wavelength of the wave. Write the formula and the steps. 

 

 

10.  

Sound

 

Sound is a form of energy that is produced by vibrations. When an object vibrates, it causes the surrounding air particles to vibrate and form sound waves. These waves travel through a medium and reach our ears, allowing us to hear.
Example:
A guitar string vibrates → air vibrates → sound reaches your ears.

Mediums of Sound Travel 

Sound needs a medium to travel. It cannot travel in a vacuum. The mediums are :

1. Solid – fastest
2. Liquid – medium
3. Gas – slowest

Reason: Particles in solids are closest together, making transmission easier.

 

Types of Sound Waves 

 Sound waves are longitudinal waves. This means the particles of the medium move back and forth in the same direction as the wave.

Compression shows particles are close together and Rarefaction shows particles are spread out.

 

Properties of Sound 

A. Loudness (Amplitude)

• Loudness depends on the amplitude of the vibration.

• Higher amplitude → louder sound

• Lower amplitude → softer sound

Unit: decibel (dB)

B. Pitch (Frequency)

• Pitch tells how high or low a sound is.

• It depends on the frequency of the sound wave.

Frequency: number of vibrations per second
Unit: Hertz (Hz)

• High frequency → high pitch (like a whistle)

• Low frequency → low pitch (like a drum)

 

C. Speed of Sound

Speed of sound depends on:

• Medium (solid > liquid > gas)

• Temperature (higher temperature → faster speed)

Average speed in air: 340 m/s

 

 D. Timbre (Quality of Sound)

• Timbre makes different sounds unique even if they have the same pitch and loudness.

• It depends on the waveform produced by different instruments.

Example:
A piano and a guitar playing the same note still sound different.

 

5. Reflection of Sound (Echo)

Sound can bounce off surfaces, especially hard surfaces.

• Echo: reflection of sound heard after a delay

• Delay happens when sound travels at least 17 meters before returning to your ear.

 

6. Absorption of Sound

Soft, porous materials can absorb sound, reducing echoes.

Examples:

• Carpets

• Curtains

• Foam panels

Used in: studios, cinemas, classrooms.

 

7. Applications of Sound

A. Sonar (Sound Navigation and Ranging)

• Uses ultrasonic waves to measure distance underwater.

B. Ultrasound

• Used in medical imaging to view internal organs.

C. Musical Instruments

• Produce sound by vibrating strings, air columns, or membranes.

   

  8. Human Hearing Range

• Humans can hear between 20 Hz to 20,000 Hz.

• Below 20 Hz → Infrasound

• Above 20,000 Hz → Ultrasound

        Animals such as bats and dolphins can hear ultrasound.

 

 Measuring Sea Depth Using Sound (SONAR)

SONAR (Sound Navigation and Ranging) is a technology that uses reflected sound waves to measure the distance to underwater objects or the ocean floor.

How It Works

1. A SONAR device sends a pulse of ultrasonic sound into the water.

2. The sound travels down until it hits the seafloor.

3. The sound wave is reflected back to the receiver on the ship.

4. The SONAR measures the time (t) taken for the sound to return.

5. Using the speed of sound in water, the depth is calculated.

Formula for Measuring Sea Depth

 

Formula for Measuring Sea Depth

$$\text{Depth} = \frac{1}{2} \times v \times t$$

Where:

• $v$ = speed of sound in water (approx 1500 m/s)

• $t$ = round-trip time (down and back)

Why divided by 2?

Because the sound travels twice:

• From the ship → to the seabed

• From the seabed → back to the ship

Example Problem

A SONAR system sends a sound pulse and receives the echo 4 seconds later.
Find the depth of the ocean.

$$\text{Depth} = \frac{1}{2} \times 1500 \times 4 = 3000 \text{ m}$$

So, the ocean is 3000 meters deep.