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Chapter 10, Section 2 Page 380-388

Chapter 10, Section 2 Page 380-388. Friction, Gravity and Elastic Forces. Friction. Friction is a force that two surfaces exert on each other when they rub against each other. When two surfaces rub, the irregularities of one surface get caught on those of the other surface

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Chapter 10, Section 2 Page 380-388

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  1. Chapter 10, Section 2Page 380-388 Friction, Gravity and Elastic Forces

  2. Friction • Friction is a force that two surfaces exert on each other when they rub against each other. • When two surfaces rub, the irregularities of one surface get caught on those of the other surface • Friction acts in a direction opposite to the object’s direction of motion • Without friction the object would continue to move at constant speed forever • Eventually friction will cause an object to come to a stop • Rough surfaces produce greater friction than smooth surfaces • Figure 4, page 381 • Foot vs. asphalt ->

  3. The Causes of Friction • In general, smooth surfaces produce less friction than rough surfaces. • Friction force depends on: • types of surfaces involved • motion of surfaces • how hard the surfaces are pressing together http://www.3m.co.uk/intl/uk//3mstreetwiseuk/flash/maggie_skating_fs.swf

  4. Static Friction • The Friction that acts on objects that are not moving. • Extra force is required to start the motion of stationary objects. • Figure 6, page 383.

  5. Sliding Friction • Occurs when two solid surfaces slide over each other. • Figure 6, page 383.

  6. Fluid Friction • Occurs when a solid object moves through a liquid. • The force needed to overcome fluid friction is usually less than that needed to overcome sliding friction • The fluid keeps surfaces from making direct contact and thus reduces friction • Figure 6, pg. 383.

  7. Rolling Friction • Occurs when an object rolls across a surface. • The force needed to overcome rolling friction is much less than the force needed to overcome sliding friction • Figure 6, page 383.

  8. Gravity and Motion • Free Fall: When the only force acting on an object is gravity. • In free fall, the force of gravity alone causes an object to accelerate in the downward direction.

  9. Elastic Forces • Matter is considered elastic if it returns to its original shape after it is squeezed or stretched. • Compression: An elastic force that squeezes or pushes matter together. • Tension: An elastic force that stretches or pulls matter. • Figure 13, pg. 388.

  10. Gravity • The force that acts to pull objects toward each other. • The force of gravity between objects increases with greater mass and decreases with greater distance. • Weight: The gravitational force exerted on a person or object at the surface of a planet. • Weight=mass x acceleration due to gravity

  11. Air Resistance • A type of fluid friction that acts on objects falling through the air. • Projectile: An object that is thrown. • Figures 11 and 12 page 387.

  12. Questions???

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