Principles of Stability
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Principles of Stability
1.Build on a firm foundation
2.Balance forces
3.Keep thrust lines vertical
4.Use rapid rotation
Thrust Lines
Student example
Principle #1: Build on a firm foundation
• Build on stable, solid ground
• Beware of climactic changes (melting, freezing, runoff water)
• Erosion
Principle #2: Balance forces
• Forces are balanced if they are...
• equal in size
• opposite in direction
• pointing along the same straight line
Balance Force: Counter Weights
• Mass that balances another mass
• Pulls in an opposite direction to a dangerous force
• Structure must withstand tension
Balance Force: Guy Wires
• Mass that balances another mass
• Pulls in an opposite direction to a dangerous force
• Structure must withstand tension
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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
Principle #3: Keep thrust lines vertical
Half-circle Arches
• distribute weight straight down
• cannot span a large space
Principle #3: Keep thrust lines vertical
Buttresses
• distribute weight straight down AND to the supporting buttresses
• can build bigger and heavier
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
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
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Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Stable or Unstable?
Experiment 1: Balancing Act
1. In groups of 2, gather materials (2 worksheets per person)
2. Roles
1. Subject - person doing experiment (balancing act)
1. ***on one foot*** (you can do both feet if it is too difficult)
2. Observer/Recorder - timer for each trial, records performance of subject
3. Switch
To Do
• Complete your “Principles of Stability” graphic organizer (*with description and colored drawing of an example)
Paper Tower Challenge