Phy2048-ch4_new - Chapter 4 Force and Motion I I Newtons first law II Newtons second law III Particular forces-Gravitational Weight Normal Friction

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I. Newton’s first law. II. Newton’s second law. III. Particular forces: -Gravitational - Weight - Normal - Friction - Tension IV. Newton’s third law. Chapter 4 – Force and Motion I
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I. Newton’s first law: If no net force acts on a body, then the body’s velocity cannot change; the body cannot accelerate b v = constant in magnitude and direction. - Principle of superposition: when two or more forces act on a body, the net force can be obtained by adding the individual forces vectorially. Newton mechanics laws cannot be applied when: 1) The speed of the interacting bodies are a fraction of the speed of light b Einstein’s special theory of relativity. 2) The interacting bodies are on the scale of the atomic structure b Quantum mechanics - Inertial reference frame: where Newton’s laws hold.
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II. Newton’s second law: The net force on a body is equal to the product of the body’s mass and its acceleration. ) 1 . 5 ( a m F net a a = ) 2 . 5 ( , , , , , z z net y y net x x net ma F ma F ma F = = = - The acceleration component along a given axis is caused only by the sum of the force components along the same axis, and not by force components along any other axis. - System: collection of bodies. - External force: any force on the bodies inside the system. III. Particular forces: -Gravitational: pull directed towards a second body, normally the Earth b ) 3 . 5 ( g m F g a a =
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) 4 . 5 ( mg W = - Weight: magnitude of the upward force needed to balance the gravitational force on the body due to an astronomical body b ) 5 . 5 ( mg N = - Normal force: perpendicular force on a body from a surface against which the body presses. - Frictional force: force on a body when the body attempts to slide along a surface. It is parallel to the surface and opposite to the motion. -Tension: pull on a body directed away from the body along a massless cord.
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: When two bodies interact, the forces on the bodies from each other are always equal in magnitude and opposite in direction. ) 6 . 5 ( CB BC F F a a - = QUESTIONS Q2. Two horizontal forces F 1 , F 2 pull a banana split across a frictionless counter. Without using a calculator, determine which of the vectors in the free body diagram below best represent: a) F 1 , b)F 2 . What is the net force component along (c) the x-axis, (d) the y-axis? Into which quadrant do (e) the net-force vector and (f) the split’s acceleration vector point? j
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This note was uploaded on 07/30/2011 for the course PHY 2049 taught by Professor Saha during the Spring '08 term at University of Central Florida.

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Phy2048-ch4_new - Chapter 4 Force and Motion I I Newtons first law II Newtons second law III Particular forces-Gravitational Weight Normal Friction

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