Integrated Science — Force and Energy

Subtopic: Waves (For students age 14 — Kenya)

Waves are a way that energy moves from one place to another without moving matter a long distance. In this note you will learn what waves are, the main types, important terms, simple formulas, examples from everyday life in Kenya, and a few short activities you can try.

Learning objectives

• Define what a wave is and give examples.
• Distinguish between transverse and longitudinal waves.
• Identify parts of a wave: crest, trough, amplitude, wavelength, frequency and period.
• Use the wave equation v = f × λ in simple calculations.
• Describe reflection, refraction and absorption of waves with local examples.

1. What is a wave?

A wave is a disturbance that transfers energy from one place to another without the permanent transfer of matter. For example, when you throw a stone into the Indian Ocean near Mombasa, ripples (waves) move outwards even though the water does not travel with the ripples forever.

2. Two main types of mechanical waves

3. Parts of a transverse wave (simple drawing)

4. Frequency and period

Frequency (f) is how many waves pass a point each second. Unit: hertz (Hz). Example: If 4 waves pass each second, f = 4 Hz.

Period (T) is the time for one full wave to pass. T = 1/f. If f = 5 Hz, then T = 1/5 s = 0.2 s.

5. Wave speed — the formula

The speed (v) of a wave is given by:

v = f × λ

Where v is in metres per second (m/s), f is frequency in hertz (Hz) and λ is wavelength in metres (m).

6. Reflection, refraction and absorption

• Reflection: Wave bounces back. Example: Echo — sound reflecting from a cliff near a valley in Kenya.
• Refraction: Wave changes direction when entering a different medium. Example: A stick looks bent in water at Lake Naivasha because light refracts.
• Absorption: Energy from the wave is taken in by the medium. Example: A wall absorbs some sound, making it quieter behind the wall.

7. Everyday examples (Kenyan context)

• Ocean waves at the Kenyan coast (Mombasa, Diani) — transverse waves on water surface.
• Sound from a roadside matatu or from a market — longitudinal waves in air.
• Light from the sun used for farming — travels as electromagnetic waves (no medium needed).
• Radio waves for FM/TV and mobile phones — carry information across distances.

8. Simple practical activities

1. String wave: Stretch a rope or strong string and move one end up and down to make transverse waves. Observe crests and troughs and count waves per second to find frequency.
2. Slinky experiment: Push and pull one end of a slinky to create compressions — this shows longitudinal waves (like sound).
3. Echo test: Stand near a cliff or tall building and clap — listen for echo (reflection of sound). Measure time between clap and echo and use speed of sound (~340 m/s) to estimate distance.
4. Water ripple test: Drop a small pebble in a basin and measure how many ripples pass a fixed point in 10 seconds to find frequency.

9. Safety and notes

• Be careful near large water bodies — do experiments in safe shallow water or a basin.
• When using loud sounds, do not stand close to speakers or repeated loud noises — protect hearing.

10. Quick revision — Key points

• Waves transfer energy, not matter.
• Transverse: motion perpendicular to direction of travel. Longitudinal: motion parallel to travel.
• Important terms: crest, trough, amplitude, wavelength (λ), frequency (f), period (T).
• Wave equation: v = f × λ (use correct units).

11. Short practice questions (with answers)

1. Define wavelength. (Answer: distance between two successive crests or troughs.)
2. If a wave has frequency 4 Hz and wavelength 0.75 m, what is its speed? (Answer: v = 4 × 0.75 = 3.0 m/s.)
3. Give one example of a longitudinal wave. (Answer: Sound in air.)
4. Explain why light can travel through space but sound cannot. (Answer: Light is an electromagnetic wave and does not need a material medium; sound needs particles to carry compressions and rarefactions.)

Prepared for Integrated Science — Force and Energy: Waves. Keep these notes for class revision and practical work. Good luck!