Presentation CHAPTER4

Presentation CHAPTER4 - 1 CHAPTER 4 NEWTONS LAWS CHAPTER 4...

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Unformatted text preview: 1 CHAPTER 4 NEWTONS LAWS CHAPTER 4 NEWTONS LAWS Newtons First Law Force and Mass Newtons Second Law Gravitational Force Contact Forces: Solids and Springs Problem Solving: Free Body Diagrams Newtons Third Law Problem Solving: Problem with Two or More Objects 2 NEWTONS FIRST LAW THE LAW OF INERTIA First law (or inertia law) : An object stay at rest or move with constant velocity in a straight line if the net force acting on an object is equal zero (forces balanced). Before Galileo and Newton was misconception that push or pull force needed keep object moving. This assumption was without understanding that force require to overcome friction. Inertia is the tendency of an object to remain at rest if it's already at rest, or to keep moving if it's already moving. 3 R a c 2 2 2 6 2 5 034 10 4 3 10 4 6 6400 10 3 7 2 3600 24 s m s m a m km R R a s rad T s T c c . . . . = = = = = = = =-- The Newtowns law work only in inertial frame of references This value is about three hundreds time lower than g . 4 Balanced Forces example The table pushes upward on the book Gravity pulls downwards on the book The table pushes upward on the book Gravity pulls downwards on the book The leftward force is exceed the friction force Unbalanced Forces example a 5 Contact Forces Action-at-a-Distance Forces Non contact forces Frictional Force Gravitational Force Tension Force Electrical Force Normal Force Magnetic Force Air Resistance Force Spring Force FORCE AND MASS The force it is vector and define by external action on an object that can causes the object to change velocity. The differences between contact forces and non contact forces are: Contact forces apply to some point or surface of the object (where contact takes place). Non contact forces apply to whole object. 6 We define Mass regarding of the Newtowns low as a Measure of the Amount of Inertia Mass is characteristic of quantity material in object. The SI unit of mass 1kg (kilogram) A object moves along strait horizontal line away from observer at constant velocity. Observer is at rest relatively to surface of the Earth. Which statement is correct. ( a ) no forces act on the object. ( b ) a constant force acts on the object in the direction of its velocity. ( c ) the net force acting on the object is zero. ( d ) the net force acting on the object it is weight. Conceptual problem: 7 A physical quantity that is sometimes described as the measure of the resistance of a body to a change in motion is A. force. B. mass. C. acceleration. D. weight. E. friction. 8 Combining Forces Multiple forces simultaneously acting on object can be combine as sum of vectors acting in one direction, direction of net force ..... + + = 2 1 F F F net 1 F 2 F 3 F 3 2 1 F F F F net + + = 9 The figure shows two forces, F 1 and F 2 , acting on an object. Which force vector best represents the resultant force on the object?...
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Presentation CHAPTER4 - 1 CHAPTER 4 NEWTONS LAWS CHAPTER 4...

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