自由落体：示例

An object is in free-fall when it falls under the influence of gravitational force alone, with no air resistance. Free-fall applies not only to objects falling downward but also to any object whose motion is influenced by gravity alone, such as a spacecraft in Earth's orbit or a projectile in motion.

In free-fall, acceleration due to gravity is constant and independent of an object's mass. When two objects are dropped from the same height and location on Earth with air resistance neglected, they experience identical gravitational acceleration and therefore reach the ground at the same speed.

Use kinematic equations for constant acceleration to solve free-fall problems. These equations relate position, velocity, acceleration due to gravity, and time. By substituting known values such as initial position, initial velocity, and elapsed time into the kinematic equations problem solving approach, you can determine the object's position and velocity at any moment.

For a freely falling object, velocity increases linearly with time because the object experiences constant acceleration due to gravity. If two objects are dropped in succession from the same location, both take the same time to reach the ground, but the first object always has greater velocity than the second.

A stone is dropped from a cliff top. Using the kinematic equations with known values of initial position, initial velocity, acceleration due to gravity, and time elapsed (5 seconds), you can calculate that the stone travels 122.5 meters and reaches a velocity of 49 meters per second after 5 seconds.

Free-fall occurs in skydiving and bungee jumping, where jumpers experience gravitational acceleration. Other examples include meteoroids accelerating toward Earth's center, spacecraft orbiting Earth, and projectile motion in two-dimensional space. All these scenarios are governed by gravitational force alone without air resistance.

Free-fall analysis assumes no air resistance. When air resistance is neglected, all objects fall with the same constant acceleration regardless of mass. In real-world scenarios, air resistance affects motion, but kinematic equations for constant acceleration provide accurate predictions when this resistance is ignored.