1. Principles of Stability

3. Principles of Stability
Build on a firm foundation
Balance forces
Keep thrust lines vertical
Use rapid rotation

4. Thrust Lines
Student example

5. Principle #1: Build on a firm foundation
Build on stable, solid ground
Beware of climactic changes (melting, freezing, runoff water)
Erosion

7. Principle #2: Balance forces
Forces are balanced if they are...
equal in size
opposite in direction
pointing along the same straight line

8. Balance Force: Counter Weights
Mass that balances another mass
Pulls in an opposite direction to a dangerous force
Structure must withstand tension

9. Balance Force: Guy Wires
Mass that balances another mass
Pulls in an opposite direction to a dangerous force
Structure must withstand tension

11. Principle #3: Keep thrust lines vertical
Problem: Center of gravity is not directly over structure = pushes outward/inward on supports (ie: think table)
Solution: distribute weight towards supports
Keeping thrust lines vertical

13. Principle #3: Keep thrust lines vertical
Half-circle Arches
distribute weight straight down
cannot span a large space

14. Principle #3: Keep thrust lines vertical
Buttresses
distribute weight straight down AND to the supporting buttresses
can build bigger and heavier

15. Principle #3: Keep thrust lines vertical
Trusses
arches with their ends tied together by a strong beam
Outward force on beam is balanced by the inward tension force

16. Principle #4: Use rapid rotation
The faster the spin the more stable
If most of the mass of a wheel is located far from the center, the greater the stability
Think...
riding a bicycle
football spiral

18. Stable or Unstable?

19. Stable or Unstable?

20. Stable or Unstable?

21. Stable or Unstable?

22. Stable or Unstable?

23. Stable or Unstable?

24. Stable or Unstable?

25. Stable or Unstable?

26. Experiment 1: Balancing Act
In groups of 2, gather materials (2 worksheets per person)
Roles
Subject - person doing experiment (balancing act)
***on one foot*** (you can do both feet if it is too difficult)
Observer/Recorder - timer for each trial, records performance of subject
Switch

27. To Do
Complete your “Principles of Stability” graphic organizer (*with description and colored drawing of an example)

28. Paper Tower Challenge