Why we can’t move on air

When it comes to understanding why we can move on solids but not on air, it’s essential to consider the principles of Newton’s laws of motion. Newton’s third law states that for every action, there is an equal and opposite reaction. In the context of movement on solids, let’s explore the reasons behind our ability to move and compare it with our inability to move on air.

1. Movement on Solids:
When we exert a force on a solid surface, such as the ground, several things happen:

a) Increased Contact:
When we apply force by pushing against a solid object, our body exerts a force on the molecules of the object’s surface. The molecules of the object come into closer contact with our body, increasing the number of molecular interactions.

b) Reaction Force:
According to Newton’s third law, as we exert a force on the solid, the molecules of the object also exert an equal and opposite force on us. This reaction force allows us to move in the direction opposite to the applied force.

For example, when we walk on the ground, our legs exert a backward force on the solid surface. As a result, the molecules of the ground push back with an equal and opposite force, propelling us forward.

2. Movement in Air:
When we try to move in air by exerting force, such as flapping our arms, the following factors come into play:

a) Limited Contact:
Unlike solids, air is a gas with molecules that are relatively far apart compared to the molecules in solids. When we exert a force on the air, only a limited number of air molecules come into contact with our body. This reduced contact area leads to fewer molecular interactions.

b) Reaction Force Insufficiency:
Due to the limited contact with air molecules, the reaction force we receive from the air is comparatively weaker than the reaction force received from solids. The weaker reaction force isn’t sufficient to overcome the gravitational pull or provide significant propulsion to move through the air.

For example, when we flap our arms, the force we exert on the air molecules is dispersed over a large volume, as air molecules are spread out. As a result, the reaction force we receive from the air is not strong enough to generate significant lift or propulsion to enable sustained flight.

In summary, we are able to move on solids because when we exert force, more molecules come into contact, leading to a stronger reaction force in accordance with Newton’s third law. In contrast, when we exert force on air, the limited contact area and the resulting weaker reaction force make it insufficient for us to move effectively through the air.