Air resistance
Air resistance is a contact force that acts against the motion of an object moving through the air. It is caused by collisions between the object and tiny air molecules. These collisions create a force that acts in the opposite direction of the object's movement, slowing it down. The amount of air resistance depends on the object's speed, shape, and surface area. Faster-moving objects experience greater air resistance because they collide with more air molecules in a shorter time. Objects with a larger surface area, such as parachutes, also experience more air resistance. To reduce this force, engineers design airplanes, racing cars, and high-speed trains with streamlined shapes so they can move more efficiently. Air resistance plays an important role in transportation, sports, and the motion of falling objects.