Presentation CHAPTER5

# Presentation CHAPTER5 - CHAPTER 5 APPLICATIONS OF NEWTONS...

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1 CHAPTER 5 APPLICATIONS OF NEWTON’S LAW Friction Drag Forces Motion Along Curved Path The Center of Mass

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2 FRICTION Polished steel surface Source of friction: Interaction between surfaces on on molecular level Nickel atoms Gold atoms Friction is physical phenomenon that appear at contact of two objects, when you move or attempt to move one object relatively another.
3 Static Friction Static friction formula Object begin to slide if magnitude applied force Where constant is called coefficient static friction. s μ n s s F f = μ max s f F g F n F Free body diagram for the block Direction of friction force always opposite direction of motion n s F F ≥ μ In case sliding block on horizontal surface the magnitude of normal force is equal to weight Friction forces Measuring coefficient static friction using incline plane

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4 Kinetic Friction Kinetic friction formula is applied to the mowing object. Constant is the coefficient of kinetic friction. k μ Usually for the same couple surfaces k s μ μ n k k F f = μ From your experience, it is difficult to start slide object but when it start it is easy to continue push. at rest In motion The figure demonstrate how friction force depend from applying force. When object moving kinetic friction force remain constant Balanced forces 1 st Newtown law
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6 g F Normal force Acting force gn F The frictional force depends only on the type of surfaces and how hard the surfaces are pressed together. Friction force We can reduce friction by lubricating the surfaces. This means that the surfaces no longer rub directly on each other, but slide past on a layer of liquid.
7 Four identical blocks of same mass are moving on a surface for which the coefficient of kinetic friction between each block and the surface is µ k . The velocity of each block is indicated by the vector on the block. For which block is the force of friction between the surface and the block greatest? A. 1 B 2 C 3 D 4 E The force of friction is the same for all blocks.

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8 Rolling Friction Rolling friction formula n r r F f = μ Constant is coefficient of rolling friction. r μ r μ Depends on nature of contacting surfaces v
Blocks made of the same material and similar shape but differing in mass lie on the bed of a truck that is moving along a straight horizontal road. When track accelerate all of the blocks will slide. What is relation between minimum accelerations to start sliding of each block with different mass ? Of these three forces, the only one that acts in the direction of the acceleration is the static friction force. Apply Newton’s 2nd law x s g s s ma mg F f = = = μ μ g a s x μ = Because a x is independent of m and F g , the critical accelerations are the same. Conceptual problem:

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Presentation CHAPTER5 - CHAPTER 5 APPLICATIONS OF NEWTONS...

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