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Transcript
SEISMIC SLEUTHS Part 1 Newton’s Laws EARTHQUAKES AND PHYSICS? • Newton’s laws • Liquefaction lab • Smart Sitting • Energy and Quakes CAN BUILDINGS BE MADE SAFER? • Building Fun • Structural Reinforcement • BOSS • Earthquake in a Box • Building Challenge • Find and Fix the Hazards • Strengthening your House Newton’s Laws of Motion: • 1st Law: Law of Inertia • Objects keep on doing what they are doing. http://www.physicsclassroom.com/mmedia/newtlaws/cci.cfm Mass is directly related to inertia. • The greater the mass the greater the tendency to resist change of an object’s motion. • objects will continue to do as they are doing with out friction. Equilibrium: if the net force on an object is zero (at rest or moving at a constant velocity) Static friction • Static friction results when the surfaces of two objects are at rest relative to one another 2nd law: Net force: something that disturbs an object’s equilibrium (net force changes an object’s velocity or acceleration) • Need to be able to find the net force (sum of all forces on an object) since net force causes an object’s acceleration http://www.physicsclassroom.com/mmedia/kinema/avd.cfm 2nd Law: acceleration of an object is proportional to the mass of the object being accelerated • F=ma – a is in m/s/s – m is in kg, – F is kgxm/s/s or Newtons • F = mg (weight) – Gravity (9.8 m/s/s) http://www.physicsclassroom.com/mmedia/newtlaws/efar.cfm Unbalanced force • The normal force is cancelled by the force of gravity. • The book is sliding to the right but there is no force in that direction. • Because SLIDING friction is currently the only horizontal force it will cause the book to come to a stop Sliding Friction • If a car slams on its brakes and skids to a stop (without antilock brakes), there is a sliding friction force exerted upon the car tires by the roadway surface. Causes of friction: • When the high points of each surface touch they bond, you must break these bonds to move one of the pieces (origin of static friction) • As surfaces move across each other, electrostatic forces continue to attract between high points, resulting in the weaker kinetic friction • Air drag (any fluid) depends on speed of the motion (getting larger as speed increases) • size and shape of object • density of fluid Forces • (Ff) Friction Force: The contact force that acts to oppose sliding motion between surfaces. Parallel to the surface Opposite the direction of sliding • Normal force (FN): The contact force exerted by a surface on an object. Perpendicular to and away from the acceleration of the object barring any resistive forces. 3rd law: • For every action there is an equal and opposite reaction http://www.physicsclassroom.com/mmedia/momentum/crete.cfm