describe what is meant by wave motion as illustrated by vibration in ropes, springs and ripple tanks

Progressive Waves

A progressive (or travelling) wave transports energy and momentum from one region of a medium to another without the permanent displacement of the medium itself. The disturbance moves through the medium while the individual particles of the medium execute only local oscillations about their equilibrium positions.

Key Characteristics

• Direction of propagation: the direction in which the wave travels.
• Amplitude (\$A\$): maximum displacement of a particle from equilibrium.
• Wavelength (\$\lambda\$): distance between successive points in phase (e.g., crest to crest).
• Frequency (\$f\$): number of oscillations per second.
• Wave speed (\$v\$): relationship given by \$v = f\lambda\$.

Illustration by \cdot ibration in a Rope

When one end of a taut rope is displaced up and down periodically, a transverse progressive wave travels along the rope. The particles of the rope move perpendicular to the direction of wave propagation.

Important observations:

1. The disturbance travels away from the source.
2. The rope itself does not move forward; each segment only moves up and down.
3. Energy is transmitted along the rope, which can be felt as a tension force at the fixed end.

Illustration by \cdot ibration in a Spring

A longitudinal wave can be demonstrated using a coiled spring. By compressing and releasing one end of the spring, a series of compressions and rarefactions travel along its length.

Key points:

• Particle motion is parallel to the direction of wave propagation.
• Each coil alternately moves closer together (compression) and farther apart (rarefaction).
• The speed of the longitudinal wave depends on the spring constant \$k\$ and the linear mass density \$\mu\$: \$v = \sqrt{\frac{k}{\mu}}\$.

Illustration by Ripple Tank

A ripple tank provides a two‑dimensional visualisation of progressive waves on the surface of water. A point source (e.g., a small vibrator) creates circular wavefronts that spread outward.

Observations in a ripple tank:

1. Wavefronts are equally spaced; the spacing equals the wavelength \$\lambda\$.
2. The crests move radially outward with speed \$v\$, satisfying \$v = f\lambda\$.
3. Interference patterns can be produced by placing multiple sources, demonstrating the superposition principle.

Comparison of the Three Demonstrations

Summary

Progressive waves are a fundamental way in which energy is transmitted through a medium. By studying simple mechanical systems—ropes, springs, and ripple tanks—students can visualise the essential features of wave motion: propagation direction, particle displacement, wavelength, frequency, and speed. These demonstrations form the experimental basis for the mathematical description of waves used throughout the A‑Level physics curriculum.