- Add new objects by double-clicking (slowly).
- Move objects by clicking and dragging.
- Throw objects (change the velocity) by Shift-clicking and
How To Use
Things To Try
The Applet's not running!
This is a simulation of a rotating space settlement without
gravity. The only forces influencing the objects in it are the
rotation of the ring. The black squares are buildings up to six
storys tall (20m on each side.) The balls are artificially large
(the size of hot-air balloons) so they can be grabbed. Objects in
free fall travel in a straight line, even if it does not appear
that way. Press "Jump" and see for yourself.
r = radius of the RingWorld (meters)
g = apparent gravity at the surface of the ring
v = velocity of ring at the surface (meters/second)
t = period of rotation (seconds)
How to Use
- Press Jump to have the balls fall off of their
- With Lock Viewpoint you can view the simulation from
afar, watching the ring rotate freely. Or you can attach (lock)
yourself to the ring so the rotation appears to stop.
- Buttons with letters in brackets [p] have keyboard short
cuts. For example, you can pause the simulation by typing 'p' (or
spacebar, too). If it does not appear to work, click inside the
ring and try again.
- To add balls to the simulation, double-click anywhere inside
the ring, or press the Random button to have a ball placed
randomly. New balls will appear with a line under them. This is a
stationary platform that rotates with the ring.
- Show Velocity Vectors will draw arrows indicating the
direction the balls would travel if left alone. Shift-Click and
drag a ball to change its velocity. Press the Shift key and hold
the mouse button down over a ball and it will turn red. Move the
mouse in the direction you want the ball to travel, and a line will
appear indicating the velocity vector you are adding to the ball's
- Click on Edit World to see the dimensions of the world.
Change the radius and the apparent gravity and see what
- If there's just too much stuff in the world, you can always
start over with Reset.
- Speed and zooming are controled with the four buttons on
the top right. The speed multiplier is shown in the upper left. For
example, '2x' means that time is passing twice as fast as in real
- Turn on Constant Speed to keep the simulation speed
steady even if the animation frame rate starts slowing down. Adding
too many objects and trails to the animation will slow your machine
down, but this mode will compensate and keep the world rotating at
a constant rate.
Why not always use this mode? This mode uses constant feedback to
maintain the simulation speed. So if the computer hiccups, you will
see the simulation jerk forward to catch up. This correcting
feedback can result in jerky animation if the browser does not give
the applet consistent time to run. I don't trust browsers so it is
left up to you turn the mode on if necessary. Experiment and see
what works best.
Things to Try
- Turn on Trails and Velocity Vectors, and unlock the viewpoint.
Notice how the trail curves, but the ball continues in a straight
line. Turn off the trails to prove that the balls are indeed moving
in a straight line.
- Lock the viewpoint and zoom in to grab a ball. Shift click a
ball and drag it towards the middle to toss the ball in the air.
See if you can get the ball to land in the same place it started.
Pausing the simulation can help in setting the velocity vector of
the ball (or multiple balls at once).
- Turn on Velocity Vectors and drag a ball around. Notice how its
velocity changes depending on the distance from the center.
Why does it change?
- Even though each ball is travelling at a constant velocity, why
do the dots in its trail spread out as if it were accelerating as
it approaches the ground? [answer]
Bugs and Enhancements
- When you click on 'Edit World' a small window pops up. If you
edit the first two parameters and click on 'Apply Changes' the
Rotational Velocity and Period of Rotation are calculated
incorrectly. Thanks to Paulo Cesar Winckler, Brazil for finding
- This applet requires Java 1.1, and most 4.x browsers do only a
fair job of running applets. Therefore this applet will probably
behave differently on different systems. I've made my best attempt
at getting this to run on various systems, but there will always be
some differences. If you have problems, find bugs, or have
suggestions, please send email to email@example.com.
Please include what machine, browser, and version of Java you are
running on, and include the Java console log if you can (under the
Web work by David
Whitney, concept by Al Globus.