Give reasons: We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert.

The ease of reaching through the air with our hands compared to reaching through a solid stick requires a mindset of resistance to the physical properties of materials and objects involved:

1. Structure of Particles: The particles in air (air molecules like nitrogen, oxygen) are widely spaced and move relatively easily. Because of the large spacing between the particles, the resistance to movement is low, allowing the hand to move easily through the air.

2. Solid Structure: In contrast, solid materials such as wood are tightly packed with particles arranged in a solid lattice structure. Close collection of molecules in a solid gives rise to strong intermolecular forces that generate large external resistance forces. This structural system makes it difficult to move through a solid material such as wood without adequate path or strength.

3. Density and Hardness: Hardwood has more density and hardness as compared to air. Its molecular complexity and density make it physically difficult for the average person to reach through without any special knowledge or technique

4. Resistance: Molecules in air provide resistance to the slightest movement of our hands due to their low density and lack of strong intermolecular forces. In other words, the molecules are tightly bound to a hardwood, giving it more resistance when trying to pass through it.

5. Human Limitations: Additionally, human power and manipulation may not be sufficient to eliminate the structural integrity of a complex object such as wood. A karate master trained in strength and precision techniques should be able to break trees due to his basic knowledge of the proper use of force.