放物運動

Projectile motion occurs when an object is launched at an angle and moves under Earth's gravitational force alone. The projectile follows a parabolic path called the trajectory. Common examples include fireworks, golf balls, and bullets. The motion combines horizontal and vertical components that can be analyzed separately.

Projectile motion can be separated into independent horizontal and vertical components because gravity acts only downward. The horizontal component of acceleration is zero, so horizontal velocity remains constant. The vertical component of acceleration equals negative g, affecting only vertical motion. This independence makes solving projectile motion equations highly convenient.

At maximum height, called the zenith, the vertical component of velocity becomes zero. However, the horizontal velocity remains constant throughout the trajectory. After reaching the zenith, the vertical velocity increases again as the projectile follows the downward trajectory. The horizontal velocity component never changes during flight.

Air resistance decreases the horizontal velocity of a projectile, reducing both its range and maximum height compared to motion in a vacuum. When deriving two-dimensional projectile motion equations, the effect of air resistance is generally neglected for simplification. This assumption allows for cleaner mathematical analysis while providing reasonable approximations for many real-world scenarios.

One-dimensional projectile motion occurs when an object falls under gravity with no horizontal movement. Two-dimensional projectile motion involves both horizontal and vertical motion components. Most practical examples, like launching fireworks or golf balls, involve two-dimensional projectile motion where motions along perpendicular axes are analyzed separately.

Choosing the launch point as the origin simplifies projectile motion analysis because it establishes a convenient reference frame. Since acceleration due to gravity always acts downward, the horizontal component of acceleration is always zero throughout the trajectory. This choice of axes makes solving projectile motion equations highly convenient and is widely used in physics.

Range is the horizontal distance covered by a projectile from launch to landing. Zenith is the maximum height the projectile reaches during its flight. Both values depend on the initial launch speed, launch angle, and gravitational acceleration. Air resistance reduces both range and zenith compared to ideal vacuum conditions.