Principles of Stability. 1. Build on a firm foundation 2. Balance forces 3. Keep thrust lines vertical 4. Use rapid rotation.

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