x: sets the initial position in the x direction of the object to be added.
vx: sets the initial velocity in the x direction of the object to be added.
y: sets the initial position in the y direction of the object to be added.
vy: sets the initial velocity in the y direction of the object to be added.
m: sets the mass of the object to be added.
dt: sets the time step.
steps per display: sets the number of time steps in between updating the animation display.