General Properties of Waves

2026 What You Need to Know (Syllabus Objectives)

By the end of these notes, you should be able to:

Core:

  1. Know that waves transfer energy without transferring matter
  2. Describe what is meant by wave motion as illustrated by vibrations in ropes and springs, and by experiments using water waves
  3. Describe the features of a wave in terms of wavefront, wavelength, frequency, crest (peak), trough, amplitude and wave speed
  4. Recall and use the equation for wave speed v = fλ
  5. Know that for a transverse wave, the direction of vibration is at right angles to the direction of propagation and understand that electromagnetic radiation, water waves and seismic S-waves (secondary) can be modelled as transverse
  6. Know that for a longitudinal wave, the direction of vibration is parallel to the direction of propagation and understand that sound waves and seismic P-waves (primary) can be modelled as longitudinal
  7. Describe how waves can undergo: (a) reflection at a plane surface (b) refraction due to a change of speed (c) diffraction through a narrow gap
  8. Describe the use of a ripple tank to show: (a) reflection at a plane surface (b) refraction due to a change in speed caused by a change in depth (c) diffraction due to a gap (d) diffraction due to an edge

Supplement: 9. Describe how wavelength and gap size affects diffraction through a gap 10. Describe how wavelength affects diffraction at an edge

1. What Are Waves?

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Waves Transfer Energy Without Transferring Matter

A wave is a way of transferring energy from one place to another without moving any material between those two places.

Think about a toy duck floating on water. When waves pass underneath the duck, it bobs up and down, but it doesn't move along with the wave. The wave travels across the water, carrying energy, but the water itself (and the duck) stays in roughly the same place.

Key point: Only the energy moves forward with the wave. The particles (like water molecules or air molecules) just vibrate back and forth around their original position. They don't travel along with the wave.

Example with water waves:

  • When you watch waves at the beach or in a pond, you might see objects floating on the surface bob up and down
  • These objects don't travel with the wave to the shore
  • This proves that the wave (energy) moves, but the matter (water) does not

Example with sound waves:

  • When someone speaks to you across a room, sound waves carry the energy of their voice to your ears
  • The air molecules in between vibrate back and forth, but they don't travel from the speaker's mouth to your ear
  • Only the sound energy makes that journey

Wave Motion

We can see wave motion clearly by looking at vibrations in ropes and springs and by doing experiments with water waves.

Vibrations in ropes:

  • If you tie one end of a rope to a fixed point and move the other end up and down quickly, you create waves that travel along the rope
  • The rope moves up and down (vibrates) but the wave travels along the length of the rope
  • The direction the rope vibrates is different from the direction the wave travels

Vibrations in springs:

  • If you have a slinky spring and push and pull one end back and forth, you create waves that travel through the spring
  • Parts of the spring bunch together (compress) and spread apart as the wave passes through
  • Here, the spring vibrates in the same direction that the wave travels

Water waves:

  • You can create water waves by dipping your finger into water or using special equipment
  • The water surface moves up and down, creating waves that spread outward in circles
  • These waves are easy to see and study, which is why we often use water in experiments

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