This is a simulation of a projectile launched at an initial speed, vo, an
initial angle, th0, and an initial height, yo. The equations of motion are
such that vx=dx/dt, vy=dy/dt, ax=Fx/m, ay=Fy/m. Here the Force is a vector
of the form Fy=-mg-b*vy, and Fx=-b*vx, where b is a coefficient of
friction (air resistance). The user has the capability to change, vo, tho,
yo, g, m, b, and dt to investigate various effects due to such changes.
Here dt is the step size used in the numerical solution process. The
method being used is the Runge Kutta solver. Making dt smaller slows the
simulation dowm but is more accurate. Increasing dt makes the calculation
run faster at the expense of accuracy.