Last reviewed: 2 November 2026
Updated November 2026. These Grade 9 notes on waves cover sub-strand 3.2 of Grade 9 Integrated Science in full: how waves are generated, transverse and longitudinal waves, the parts of a wave and the wave equation, how waves behave, remote sensing, and the uses of waves in medicine, communication and cooking. Each part has a short explanation, a worked example and a quick check, so a learner can revise the whole topic in one sitting.
The content follows the Waves sub-strand in the KICD Grade 9 Integrated Science curriculum design, which suggests about 16 lessons for it under Strand 3.0, Force and Energy.
On this page
What Is a Wave? Grade 9 Waves Notes Basics
A wave is a disturbance that carries energy from one place to another without carrying the material (the medium) along with it. When you drop a stone in a basin of water, ripples spread out, but a floating leaf only bobs up and down: the energy moves outwards, the water stays roughly where it was.
Waves are generated by vibrations. Shaking one end of a skipping rope, pushing and pulling a slinky spring, a vibrating loudspeaker cone or a guitar string all start waves. No vibration, no wave.
Transverse and Longitudinal Waves
| Transverse waves | Longitudinal waves | |
|---|---|---|
| How particles vibrate | At right angles to the direction the wave travels | Back and forth along the direction the wave travels |
| Shape | Crests (high points) and troughs (low points) | Compressions (particles squeezed together) and rarefactions (particles spread out) |
| Examples | Water ripples, a rope shaken up and down, light and radio waves | Sound waves, a slinky pushed and pulled along its length |
Quick check: a slinky can make both types. Shake it sideways and you get a transverse wave; push and pull it along its length and you get a longitudinal wave.
Parts of a Wave and the Wave Equation
- Amplitude: the maximum displacement of a particle from its rest position. A bigger amplitude means more energy (a louder sound, a taller ripple).
- Wavelength (λ): the distance between two neighbouring crests (or two compressions), in metres.
- Frequency (f): the number of complete waves produced per second, in hertz (Hz).
- Period (T): the time taken to produce one complete wave, in seconds. T = 1 ÷ f.
- Wave speed (v): the distance the wave travels per second, in metres per second.
- Phase: two points are in phase when they are at the same stage of their vibration at the same time, for example two crests.
The wave equation in the design is velocity = wavelength × frequency, or v = fλ.
Worked example 1: a radio station broadcasts at 100 MHz (100,000,000 Hz). Radio waves travel at about 300,000,000 m/s. Wavelength = v ÷ f = 300,000,000 ÷ 100,000,000 = 3 m.
Worked example 2: a learner counts 10 ripples passing a stick in 5 seconds. Frequency = 10 ÷ 5 = 2 Hz, so the period T = 1 ÷ 2 = 0.5 s. If the ripples are 0.3 m apart, speed = 2 × 0.3 = 0.6 m/s.
How Waves Behave
The design asks learners to demonstrate four characteristics using a basin of water or a ripple tank:
- Waves travel in straight lines in the same medium.
- Reflection: waves bounce off a barrier, like an echo bouncing off a wall.
- Bending (refraction): waves change direction when they pass into a different medium or depth, because their speed changes.
- Moving around objects (diffraction): waves spread around obstacles and through gaps, which is why you can hear someone talking round a corner.
Remote Sensing and Waves
Remote sensing means collecting information about an object or area without touching it, by detecting waves (electromagnetic radiation) that it reflects, absorbs or gives off. Different surfaces respond differently at different wavelengths: healthy crops reflect a lot of infrared, water absorbs most of it, so satellite images can show crop health, flooding or forest cover.
- Passive remote sensing uses natural energy, mostly sunlight reflected from the Earth (for example ordinary satellite photographs).
- Active remote sensing sends out its own waves and measures what returns (for example radar).
- Platforms carry the sensors: satellites, aircraft and drones.
The design links this sub-strand to careers, so mention that remote sensing is used in weather forecasting, mapping and agriculture.
Uses of Waves in Day-to-Day Life
| Area | Examples named in the Grade 9 design |
|---|---|
| Medicine | Ultrasound scans (high-frequency sound), X-rays, CT scans, MRI scans, cancer therapy, laser surgery |
| Communication | Radar, radio, mobile phones, television, Wi-Fi, controlling drones |
| Cooking | Microwave ovens |
Note that ultrasound is a sound (longitudinal) wave, while X-rays, radio waves, microwaves and light are electromagnetic (transverse) waves.
Common Mistakes
- Saying waves carry matter. They carry energy.
- Measuring wavelength from a crest to the next trough (that is half a wavelength).
- Forgetting to convert kHz or MHz to Hz before using v = fλ.
- Calling sound a transverse wave.
Revise the Rest of Grade 9 Integrated Science
Waves sits alongside curved mirrors in the Force and Energy strand. Our Grade 9 Integrated Science revision guide covers nutrition, mirrors, atoms and metals, the Grade 9 water hardness notes cover sub-strand 1.3, and the Grade 9 Integrated Science curriculum overview lists every sub-strand. In KJSEA, the KNEC KJSEA regulations set Integrated Science as two papers: 905/1 (70 marks) and 905/2 (30 marks, practical skills in chemistry, biology and physics).
Practise free on the Grade 9 CBC Challenge, then sit a timed Grade 9 Integrated Science practice paper. All Grade 9 subjects are on the Grade 9 notes hub.
Frequently Asked Questions
What is the difference between transverse and longitudinal waves?
In transverse waves the particles vibrate at right angles to the direction of travel, forming crests and troughs. In longitudinal waves they vibrate along the direction of travel, forming compressions and rarefactions. Light is transverse; sound is longitudinal.
What is the wave equation in Grade 9?
Velocity = wavelength × frequency (v = fλ). Speed is in m/s, wavelength in metres and frequency in hertz. The period is T = 1 ÷ f.
What is remote sensing in Grade 9 Integrated Science?
Collecting information about objects or places without touching them, by detecting waves they reflect, absorb or emit. It can be passive (using sunlight) or active (sending out its own waves, like radar), from satellites, aircraft or drones.
Can I download these Grade 9 waves notes as a PDF?
Yes. Open the page and use your browser’s print option, then choose “Save as PDF”.
Want marked practice? The first questions of each paper are free. A Day Pass (KSh 20) unlocks the full Grade 9 Integrated Science practice papers with worked answers for a day, or choose the Monthly Pass (KSh 500) for every grade and subject all month. Compare passes.