Principles of Stability
QuickTime™ and a decompressor
are needed to see this picture.
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
QuickTime™ and a decompressor
are needed to see this picture.
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
QuickTime™ and a decompressor
are needed to see this picture.
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
