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Gravity and air resistance are two opposing forces that determine how objects move through Earth's atmosphere. While gravity is a constant downward force pulling all objects toward the Earth's center at a rate of
(in a vacuum), air resistance (or drag) is a friction-like force that opposes the motion of objects moving through the air.

Key Concepts
Opposing Forces: Air resistance acts opposite to the direction of motion. When an object falls, gravity pulls it down while air resistance pushes up.
Factors Affecting Air Resistance:
Surface Area: Larger surface areas encounter more air resistance (e.g., a flat piece of paper vs. a crumpled one).
| Speed: Faster objects encounter greater air resistance.
Terminal Velocity: When an object falls long enough, air resistance builds up until it equals the force of gravity. At this point, the net force is zero, and the object stops accelerating, falling at a constant speed known as terminal velocity.
Mass Independence: In the absence of air (like on the Moon), all objects fall at the same rate regardless of mass. Air resistance, not gravity, is why a feather falls slower than a hammer on Earth.
| Gravity and the Atmosphere |
Holding the Atmosphere: Gravity prevents the atmosphere from drifting into space.
Air Pressure: Gravity pulls air molecules toward the ground, creating higher density and air pressure at lower altitudes.
Pressure Gradient: The atmosphere doesn't completely collapse to the ground because the air beneath it exerts an upward pressure, counteracting the downward pull of gravity.

Everyday Examples
Parachutes: A parachute increases surface area, creating high air resistance to slow a skydiver's descent.
Falling Paper: A flat sheet of paper experiences high air resistance due to its large surface area, causing it to fall slowly, whereas a crumpled sheet has less surface area and falls faster.
Vehicles: Fast cars are designed to be streamlined to reduce air resistance.
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