Which is an example of a mechanical wave?

• A. Light wave
• B. Gamma ray
• C. Sound wave
• D. Radio wave

Answer: (C)

Mechanical waves transfer energy by making the particles of a material vibrate as the wave moves through it. Sound is a classic example because it needs a medium—air, water, or a solid—to travel. As sound moves, it creates regions of compression and rarefaction in the medium, with particles oscillating in the same direction as the wave. This relies on interactions between particles in matter, so without a medium there’s no way for the disturbance to propagate. In contrast, light, gamma rays, and radio waves are electromagnetic waves. They don’t require a medium and can travel through vacuum, propagating as oscillating electric and magnetic fields. That fundamental difference is what makes sound the mechanical wave. The speed of a mechanical wave also depends on the medium, being different in air, water, and solids.