This is a home work problem shown in many Fundamental Physics textbooks .

• How to stack four uniform blocks on top of a table, so that they extend as far right as possible and still remain stable.
• How should each be positioned?
• Can the top block have its entire length beyond the edge of the table.
• Would you like to play!

• So long as the center of gravity is directly above some point within area of support, the system will be stable

1. You can drag and move blocks horizontal with your mouse.
2. The stability of the sub-system is color coded
1. Green: the sub-system is in stable equilibrium
2. yellow: the center of gravity is right above the edge of the supporting block.
3. red: the sub-system is unstable, it will fall in real life.
3. The center of gravity for each block is shown as a small blue dot.
4. If you press "Show c.g." button
1. The center of gravity for the blocks being moved will be shown as a small circle.
2. The length of the arrow is proportional to the gravitational force for each balanced sub-system.
3. Label of this button change to "Hide c.g", and you know what it means.
5. Current mouse position is shown in the "Text Field" (relative to top left edge of the table)
6. The percentage to the max. distance is shown on right edge of top block. It will smile when you get 100%
7. All the other numbers are coordinates measured from the left edge of the current window and they are all color coded.

The left edge of each block under the number

The center of gravity of each block the number is in

The center of gravity for all the blocks above the number

How to make it better? Do I need to make blocks falling down if it is unstable? Will it help the students learn more about the concept of center of gravity ?