When a pinwheel is placed against the wind and begins to spin, it proves that moving air has energy. Let's break down the answer and explain it in detail.

1. Moving Air Has Energy:
The spinning of a pinwheel when placed against the wind clearly demonstrates that the moving air possesses energy. This energy is transferred to the pinwheel, causing it to rotate. Air in motion is called wind, and wind energy is a form of kinetic energy. When the wind blows, it carries this energy with it.

2. Pinwheel's Design:
The design of a pinwheel allows it to capture the energy from the moving air. A pinwheel consists of several blades or vanes attached to a central axis. The blades are typically shaped like sails or propellers. When the wind blows, it encounters the blades, exerting a force on them. This force causes the blades to rotate around the axis.

3. Conservation of Energy:
The spinning motion of the pinwheel is a result of the conservation of energy principle. According to this principle, energy cannot be created or destroyed but can only be transferred or converted from one form to another. In this case, the energy in the moving air is transferred to the pinwheel, causing it to spin.

4. Wind as a Renewable Energy Source:
The fact that moving air has energy is significant in the context of renewable energy. Wind energy is a clean and renewable source of power that can be harnessed using wind turbines. These turbines work on a similar principle to pinwheels, but on a much larger scale. The wind turns the blades of the turbine, which then generate electricity.

Conclusion:
The spinning of a pinwheel when placed against the wind is evidence that moving air has energy. This energy is transferred to the pinwheel, causing it to rotate. Understanding the energy present in moving air is crucial in harnessing wind power for various applications, including generating electricity.