• Document: Chapter 4: Newton's Second Law of Motion
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Lecture Outline Chapter 4: Newton's Second Law of Motion © 2015 Pearson Education, Inc. This lecture will help you understand: •  Force Causes Acceleration •  Friction •  Mass and Weight •  Newton's Second Law of Motion •  Free Fall •  Nonfree Fall © 2015 Pearson Education, Inc. Force Causes Acceleration •  Acceleration is directly proportional to net force. •  To increase the acceleration of an object, increase the net force acting on it. Acceleration ~ net force © 2015 Pearson Education, Inc. The Force of Friction •  Depends on the kinds of material and how much they are pressed together. •  Is due to tiny surface bumps and to "stickiness" of the atoms on a material's surface. •  Example: Friction between a crate on a smooth wooden floor is less than that on a rough floor. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR NEIGHBOR The force of friction can occur A.  with sliding objects. B.  in water. C.  in air. D.  All of the above. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR ANSWER The force of friction can occur A.  with sliding objects. B.  in water. C.  in air. D.  All of the above. Comment: Friction can also occur for objects at rest. If you push horizontally on your book and it doesn't move, then friction between the book and the table is equal and opposite to your push. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR NEIGHBOR When Sanjay pushes a refrigerator across a kitchen floor at a constant speed, the force of friction between the refrigerator and the floor is A.  less than Sanjay's push. B.  equal to Sanjay's push. C.  equal and opposite to Sanjay's push. D.  more than Sanjay's push. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR ANSWER When Sanjay pushes a refrigerator across a kitchen floor at a constant speed, the force of friction between the refrigerator and the floor is A.  less than Sanjay's push. B.  equal to Sanjay's push. C.  equal and opposite to Sanjay's push. D.  more than Sanjay's push. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR NEIGHBOR When Sanjay pushes a refrigerator across a kitchen floor at an increasing speed, the amount of friction between the refrigerator and the floor is A.  less than Sanjay's push. B.  equal to Sanjay's push. C.  equal and opposite to Sanjay's push. D.  more than Sanjay's push. © 2015 Pearson Education, Inc. The Force of Friction CHECK YOUR NEIGHBOR When Sanjay pushes a refrigerator across a kitchen floor at an increasing speed, the amount of friction between the refrigerator and the floor is A.  less than Sanjay's push. B.  equal to Sanjay's push. C.  equal and opposite to Sanjay's push. D.  more than Sanjay's push. Explanation: The increasing speed indicates a net force greater than zero. The refrigerator is not in equilibrium. © 2015 Pearson Education, Inc. Mass and Weight •  Mass: The quantity of matter in an object. It is also the measure of the inertia or sluggishness that an object exhibits in response to any effort made to start it, stop it, or change its state of motion in any way. •  Weight: Usually the force upon an object due to gravity. © 2015 Pearson Education, Inc. Mass and Weight •  Mass –  A measure of the inertia of a material object –  Independent of gravity Greater inertia ⇒ greater mass –  Unit of measurement is the kilogram (kg) •  Weight –  Usually the force on an object due to gravity –  Scientific unit of force is the newton (N) –  Unit is also the pound (lb) © 2015 Pearson Education, Inc. Mass—A Measure of Inertia CHECK YOUR NEIGHBOR If the mass of an object is halved, the weight of the object is A.  halved. B.  twice. C.  depends on location. D.  None of the above. © 2015 Pearson Education, Inc. Mass—A Measure of Inertia CHECK YOUR ANSWER If the mass of an object is halved, the weight of the object is A.  halved. B.  twice. C.  depends on location. D.  None of the above. Comment: Weight and mass are directly propor

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