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Forces: Friction and Tension

Forces: Friction and Tension. The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it . Opposes motion. What is Friction?. The amount of friction between two surfaces depends on two factors The kinds of surfaces

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Forces: Friction and Tension

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  1. Forces: Friction and Tension

  2. The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. • Opposes motion What is Friction?

  3. The amount of friction between two surfaces depends on two factors • The kinds of surfaces • The force pressing the surfaces together • Friction is caused by the rough surfaces of objects • ALL objects have a rough surface, even if it’s only on a microscopic level Friction

  4. Static Friction= the frictional force that prevents two surfaces from sliding past each other • The reason its harder to start pushing than to continue pushing the same object • Kinetic Friction= when two objects are moving relative to each other and rub together (like a sled on the ground) • Sliding Friction=the frictional force that opposes the option of two objects sliding past each other • Rolling Friction=frictional force between a rolling object and the surface it rolls on Types of Friction

  5. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula below: • Ff= µFN • µ is the coefficient of friction • The value of μ provides a measure of the relative amount of adhesion or attraction of the two surfaces for each other. • The more that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force. Friction

  6. Fg=weight=mg • Ff=µFN • Fnet=FA + (-Ff) Friction

  7. A desk has a mass of 2.5 kilograms. If the coefficient of static friction between the desk and the floor is 0.04, what force must be used to move the desk from rest? • What force must be used to keep it moving at a constant velocity if the coefficient of kinetic friction is 0.0267? Friction

  8. the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends • The tension force is directed along the length of the wire and pulls equally on the objects on the opposite ends of the wire. What is Tension?

  9. What other forces could be involved? • If an object is hanging or moving up/down: • FT • Fg • If an object is being moved sideways: • FT (replaces FA) • Fg • FN • Ff Tension

  10. When we do tension problems we assume the rope/chain/string is massless • If a pulley is involved we assume there is no friction between the pulley and the rope • Basically, we are only considering the forces directly on the object Tension

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