Projectile motion
Idealized motion under gravity alone, following a parabolic path.
Projectile motion describes the motion of an object launched into the air and moving under the influence of gravity alone, with air resistance neglected. In this idealized model, the object follows a parabolic path determined by its initial velocity and the constant acceleration due to gravity. The motion can be decomposed into horizontal and vertical components: the horizontal motion occurs at a constant velocity, while the vertical motion experiences uniform acceleration.
- field
- Physics, Classical Mechanics, Ballistics
- known_for
- Parabolic trajectory of projectiles under gravity, principle of compound motion
- key_concept
- Horizontal and vertical motion are independent; trajectory is parabolic except when thrown directly upward or downward
Lore & Background
Galileo Galilei showed that the trajectory of a given projectile is parabolic, but the path may also be straight in the special case when the object is thrown directly upward or downward. The study of such motions is called ballistics, and such a trajectory is described as ballistic. The force of mathematical significance that is actively exerted on the object is gravity, which acts downward, thus imparting to the object a downward acceleration towards Earth's center of mass. Due to the object's inertia, no external force is needed to maintain the horizontal velocity component of the object's motion.
Reader's Guide
Projectile motion lies at the heart of classical mechanics and is fundamental to a wide range of applications—from engineering and ballistics to sports science and natural phenomena. The elementary equations of ballistics neglect nearly every factor except for initial velocity, the launch angle and a gravitational acceleration assumed constant. Practical solutions of a ballistics problem often require considerations of air resistance, cross winds, target motion, acceleration due to gravity varying with height, and in such problems as launching a rocket from one point on the Earth to another, the horizon's distance vs curvature R of the Earth. Detailed mathematical solutions of practical problems typically do not have closed-form solutions, and therefore require numerical methods to address. A ballistic missile is a missile only guided during the relatively brief initial powered phase of flight, and whose remaining course is governed by the laws of classical mechanics.
Did You Know?
- In projectile motion, the horizontal motion and the vertical motion are independent of each other; neither motion affects the other.
- A ballistic trajectory is a parabola with homogeneous acceleration, such as in a space ship with constant acceleration in absence of other forces.
- If an object was thrown and the Earth was suddenly replaced with a black hole of equal mass, the ballistic trajectory would be part of an elliptic orbit around that black hole.
More in Classical And Fluid Mechanics 1-19
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