function [p, v] = freefall_step ( p, v, dt )

% Takes position, velocity vectors and a time interval, and calculates
% the final position and velocity vectors, returning them as [x, v].

% Position and velocity vectors are 3x1.

% Only external force is gravity, in z direction.

g = 9.8;	% Metric
% English units or not?

p(1) = p(1) + v(1)*dt;			% x = x + Vx*dt
p(2) = p(2) + v(2)*dt;			% y = y + Vy*dt
p(3) = p(3) + v(3)*dt - .5*g*dt*dt;	% z = z + Vz*dt - (1/2)g*dt^2

v(3) = v(3) - g*dt;			% Vz = Vz - g*dt
% All other values - Vx and Vy - remain the same.