Friction
Friction is the force that slows things down when they rub against each other.
Think of it this way
When you slide a wooden cutting board across a dry countertop, it moves slowly and stops fast. The rough surfaces grip each other and push back against the motion. Pour a thin layer of water under the board and it glides much faster. Less contact between the surfaces means less friction slowing it down.
Explaining friction by grade level
When wind blows close to the ground, grass and trees slow it down. That drag happens because the air rubs on rough things. Up high, there is less to rub on, so wind moves faster. The rubbing force that slows it is called friction.