AstroGrav Help /Sample Simulations /Abstract Systems /ProjectileVersion 5.2

# Projectile

This simulation illustrates the motion of a small projectile on the Earth, and its collision with a much larger ball. Two view windows have been provided - a high magnification view showing the projectile and ball clearly with the Earth so much magnified that its surface appears flat, and a low magnification view showing the entire Earth with the projectile and ball too small to be visible. Because the Sun is not present in the simulation, the Earth has been made luminous so that you can see what's going on.

If you set the simulation running, you can watch how it evolves, and see how the projectile follows its orbit until it collides with the Earth, bounces three times before hitting the bouncing ball, and eventually the projectile and ball come to rest. You can then stop the simulation running, use Edit / Undo (or File / Revert to Saved) to return to its initial state, move the 'Low Magnification' view window to the front, edit the Earth to have a much smaller radius (such as 1 km), and then see how the near-parabolic paths of the projectile and ball are really just the distal ends of highly eccentric elliptical orbits. If you set this alternative simulation running, you can watch how it evolves, and see how long it takes the projectile and ball to fall to the modified Earth.

You can also try editing the projectile's properties - particularly its absolute velocity - to see how it affects the projectile's path. You will find that if you change the z-component of the absolute velocity to 0, and the y-component of the absolute velocity to about 7.91 km/s, the projectile will travel fast enough to orbit the Earth in a circular orbit. Making the y-component of the absolute velocity larger still produces more and more eccentric orbits, until at a value of 11.19 km/s the orbit becomes hyperbolic. 11.19 km/s is the Earth's escape velocity.

Since different computers run at different speeds, you may need to edit the evolution time step to get the simulation to run at an acceptable rate.