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Stick-Slip Activity Intro

Stick-Slip Activity Intro. Exploring an earthquake model. +. =. ?. What is Stick-Slip?. The jerking motion that often occurs when two surfaces are sliding over each other. The surfaces alternate between sticking and slipping Common examples Music from a violin (bow across string)

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Stick-Slip Activity Intro

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  1. Stick-Slip Activity Intro Exploring an earthquake model Mark Harms 10/31/08

  2. + = ? Mark Harms 10/31/08

  3. What is Stick-Slip? • The jerking motion that often occurs when two surfaces are sliding over each other. • The surfaces alternate between sticking and slipping • Common examples • Music from a violin (bow across string) • Sound of noisy brakes on a car • Screeching car tires • Glass Harp (wet finger around the rim of a wine glass) Mark Harms 10/31/08

  4. What is Required for Stick-Slip? • The force required to “un-stick” the surfaces is greater than the force required to keep the surfaces moving. • The static coefficient of friction must be higher than the kinetic coefficient of friction • A force that varies with displacement is also required. • An elastic (“springy”) material stores elastic energy as it deforms and could supply such a force. • Rigid materials are elastic to some degree – even rock! Mark Harms 10/31/08

  5. The Stick-Slip Cycle One cycle of stick-slip: • Surfaces are stuck • An external shear force is applied (continuously) • Elastic material deforms, storing elastic energy • Surfaces remain stuck, since the force delivered to the contact area is less than the force needed to overcome static friction • Eventually the force at the contact area overcomes static friction – the surfaces begin to slide • Stored energy in the elastic material is released, causing the surfaces to accelerate as they slide past each other • As the elastic material returns to its previous shape (elastic rebound) the force delivered to the surfaces decreases until it can no longer overcome kinetic friction and the surfaces stop moving • The surfaces are stuck again Mark Harms 10/31/08

  6. Stick-Slip on an Earthquake Fault “Stick” “Slip” Mark Harms 10/31/08

  7. + = Friction along fault segment Deformed rocks store elastic potential energy Elastic energy released! EARTHQUAKE! Mark Harms 10/31/08

  8. Earthquake Slip Activity • Demo • Workshop Activity Mark Harms 10/31/08

  9. Vocabulary • Creep: Slow, steady fault movement. • Deformation: The change in shape of an object as a result of the application of stress to it. • Elasticity: The property of returning to an initial form following deformation. • Elastic rebound: As plates move, elastic strain energy builds along edges, until rocks rupture and return to their undeformed shapes. • Strain: deformation of the earth. • Static friction: The force between two objects that are not moving relative to each other. Friction that keeps things from moving. • Stress: A force applied over an area. • Stick-slip: Adjacent surfaces alternating between sticking to each other and sliding past each other. Mark Harms 10/31/08

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