Principles of Stability Principles of Stability 1 Build

Principles of Stability

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

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

Stable or Unstable?

Experiment 1: Balancing Act 1. In groups of 2, gather materials (2 worksheets 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