Mrs. Nowlan's Grade 7 Science

Unit 4: Structures and Forces

Topic 5:How structures fail

Concepts:

• identify modes of structure failure
• identify forces within a structure and describe how these forces cause a structure to fail

Definitions

Lever: is a device that can change the amount of force needed to move an object e.g crowbar.

Fulcrum: the pivot or point on which a level rests.

Internal forces: forces caused by external forces that cause failure. Solid materials have microscopic cracks that are weakened by external forces.

Shear: slipage along cracks e.g earthquake movement on land

Bend or Buckle: caused by compression forces

Torsion: twisting forces cause failure in brittle, hard materials but deform softer materials such are rubber.

Metal fatique: metal weakens over time when it is bent and twisted again and again because the particles are re-arranged into a weaker state