Formula and Method for Projectile Motion Trajectory
Projectile motion describes the curved path — a parabola, in the absence of air resistance — traced by an object launched into the air and acted on only by gravity. The motion splits cleanly into two independent components: a constant horizontal velocity and a uniformly accelerated vertical velocity. That separation is what lets this calculator solve directly for flight time, maximum height, horizontal range, and landing speed from the launch conditions.
How the calculation works
The launch velocity v0 is split into horizontal and vertical components using the launch angle θ: vx = v0 cos θ and vy = v0 sin θ. Because gravity acts only vertically, vx stays constant for the entire flight while vy decreases (then reverses) at a constant rate g. Solving the vertical position equation h0 + vy·t − ½gt² = 0 for the moment the projectile reaches the ground gives the time of flight, t = [v0 sinθ + √((v0 sinθ)² + 2gh0)] / g. Multiplying the constant horizontal speed vx by that time gives the horizontal range, R = vx·t. Maximum height is reached when the vertical velocity hits zero, at H = h0 + (v0 sinθ)² / (2g). Impact speed follows directly from energy conservation — ½v0² + gh0 = ½v_impact² — so v_impact = √(v0² + 2gh0).
Common mistakes and modeling limits
- Degrees vs. radians: the launch angle is entered in degrees here; if you check the math by hand in code, remember that sin() and cos() functions typically expect radians (multiply degrees by π/180 first).
- Forgetting launch height: leaving h0 at 0 when a projectile is actually launched from a platform, cliff, or elevated release point understates both flight time and range.
- No air resistance: this calculator uses ideal, drag-free kinematics. Real projectiles — especially light or slow-moving ones — lose range and height to air drag, and spinning projectiles curve further due to the Magnus effect.
- 45° isn't always optimal: a 45° launch angle only maximizes range when launch and landing heights are equal. Launching from above the landing point, the optimal angle is slightly below 45°.
Real-world applications
- Sports: estimating the range of a thrown ball, golf shot, or javelin throw from launch speed and angle.
- Ballistics: estimating flight time and impact point for a known muzzle velocity and elevation angle as a first-pass, drag-free estimate.
- Engineering and safety: sizing catch nets, clearance heights, or exclusion zones around launch or ejection equipment.
- Physics education: verifying the classic results that range is maximized at 45° and that flight time depends only on the vertical velocity component.