09Lecture_3 - Physics 1112: Lecture 3 Todays Agenda 1-D...

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Physics 112: Lecture 3, Pg 1 Physics 1112: Lecture 3 Physics 1112: Lecture 3 Today Today ’s Agenda s Agenda 1-D free fall example Review of Vectors

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Physics 112: Lecture 3, Pg 2 Review: Review: For constant acceleration we found: x a v t t t From which we derived: x = x 0 + v 0 t + 1 2 at 2 v = v 0 + at a = const v 2 " v 0 2 = 2a(x " x 0 )
Physics 112: Lecture 3, Pg 3 1-D Free-Fall 1-D Free-Fall This is a nice example of constant acceleration (gravity): In this case, acceleration is caused by the “force of gravity”: MORE ON FORCES LATER Usually pick y-axis “upward” Acceleration of gravity is “down”: y a y = g y a v t t t y = y 0 + v 0 y t " 1 2 g t 2 v y = v 0 y " g t a y = " g

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Physics 112: Lecture 3, Pg 4 1-D Free-Fall 1-D Free-Fall This is a nice example of constant acceleration (gravity): In this case, acceleration is caused by the “force of gravity”: MORE ON FORCES LATER Usually pick y-axis “upward” Acceleration of gravity is “down”: y a y = g y a v t t t y = y 0 + v 0 y t " 1 2 g t 2 v y = v 0 y " g t a y = " g
Physics 112: Lecture 3, Pg 5 Gravity facts: Gravity facts: g does not depend on the nature of the material! Galileo (1564-1642) demo - freefall in vacuum Nominally, g = 9.81 m/s 2 At the equator g = 9.78 m/s 2 At the north pole g = 9.83 m/s 2 More on gravity in a few lectures! Freefall in vacuum This course: g = 9.8 m/s 2

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Physics 112: Lecture 3, Pg 6 Problem: Problem: The pilot of a hovering helicopter drops a lead brick from a height of 1000 m. How long does it take to reach the ground and how fast is it moving when it gets there? (neglect air resistance) 1000 m
Physics 112: Lecture 3, Pg 7 Problem: Problem: First choose coordinate system. Origin and y -direction. Next write down position equation: Realize that v 0y = 0 . 1000 m y = 0 y y = y 0 + v 0y t 1 2 gt 2 y = y 0 " 1 2 gt 2

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Physics 112: Lecture 3, Pg 8 Problem: Problem: Solve for time t when y = 0, given that y 0 = 1000 m. Recall: Solve for v y : v y = -9.8 m/s 2 x 14.3 s = - 140 m/s y 0 = 1000 m y y = 0 t = 2 y 0 g = 2 " 1000 m 9.81 m s 2 = 14.3 s v y = v 0 y " g t
Physics 112: Lecture 3, Pg 9 Modeling Modeling Treated brick as point particle Ignored air resistance, wind “Gravity” Model for kinematics: free fall has constant acceleration

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This note was uploaded on 02/25/2009 for the course PHYS 1112 taught by Professor Leclair,a during the Spring '07 term at Cornell University (Engineering School).

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09Lecture_3 - Physics 1112: Lecture 3 Todays Agenda 1-D...

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