* Mechanical waves require a medium (like air, water, or a solid) to travel. They are disturbances that travel through this medium by causing particles to vibrate.

Let's break down the options:

* A glass of water: While water can carry waves, this is not a wave itself. It's simply a substance.

* A shovel full of dirt: This is a static object. There's no movement or disturbance that could create a wave.

* A light bulb: Light bulbs emit electromagnetic waves, which do not require a medium to travel. They are a different type of wave than mechanical waves.

* Noise from a car horn: This is a sound wave, which is a mechanical wave that travels through the air. The horn's vibrations create disturbances in the air molecules, causing them to vibrate and transmit the sound to your ears.

In summary: Only the sound from a car horn is a clear example of a mechanical wave.