康涅狄格州大学：《普通物理》课程PPT教学课件（英文版）Lecture 8 An Example

Physics 121, Sections 9, 10, 11, and 12 Lecture 8 Today's Topics Homework 3: Due Friday Sept 23@ 6: 00PM Ch.3:#64,75,and81 Ch4:#4,8,21,25,36,40,and51 Chapter 4: Motion in 2-D More examples of FBD's Examples with friction Physics 121: Lecture 8, Pg 1

Physics 121: Lecture 8, Pg 1 Physics 121, Sections 9, 10, 11, and 12 Lecture 8 Today’s Topics: Homework 3: Due Friday Sept. 23 @ 6:00PM Ch.3: # 64, 75, and 81. Ch.4: # 4, 8, 21, 25, 36, 40, and 51. Chapter 4: Motion in 2-D More examples of FBD’s Examples with friction

An Example Consider the following two cases Physics 121: Lecture 8, Pg 2

Physics 121: Lecture 8, Pg 2 An Example Consider the following two cases

An Example The Free Body Diagrams mg FBT N mg Ball falls For static Situation mg Physics 121: Lecture 8, Pg 3

Physics 121: Lecture 8, Pg 3 An Example The Free Body Diagrams mg mg FB,T= N Ball Falls For Static Situation N = mg

An Example The action/reaction pair forces B,E"-mg F BT N B.EF-mg EB=mg EB= mg Physics 121: Lecture 8, Pg 4

Physics 121: Lecture 8, Pg 4 An Example The action/reaction pair forces FB,E = -mg FB,T= N FE,B = mg FB,E = -mg FE,B = mg FT,B= -N

Lecture 8. ACT 1 Gravity and Normal Forces a woman in an elevator is accelerating upwards The normal force exerted by the elevator on the woman is A) greater than B)the same as C)less than the force due to gravity acting on the woman Physics 121: Lecture 8, Pg 5

Physics 121: Lecture 8, Pg 5 Lecture 8, ACT 1 Gravity and Normal Forces A woman in an elevator is accelerating upwards The normal force exerted by the elevator on the woman is, A) greater than B) the same as C) less than the force due to gravity acting on the woman

Lecture 8 ACT1b Gravity and Normal Forces a woman in an elevator is accelerating upwards The normal force exerted by the elevator on the woman is A) greater than B)the same as C)less than the force the woman exerts on the elevator Physics 121: Lecture 8, Pg 6

Physics 121: Lecture 8, Pg 6 Lecture 8, ACT 1b Gravity and Normal Forces A woman in an elevator is accelerating upwards The normal force exerted by the elevator on the woman is, A) greater than B) the same as C) less than the force the woman exerts on the elevator

The Free Body Diagram Newton's 2nd Law says that for an object F= ma Key phrase here is for an object. So before we can apply F= ma to any given object we isolate the forces acting on this object Physics 121: Lecture 8, Pg 7

Physics 121: Lecture 8, Pg 7 The Free Body Diagram Newton’s 2nd Law says that for an object F = ma. Key phrase here is for an object. So before we can apply F = ma to any given object we isolate the forces acting on this object:

The Free Body Diagram ■■ Consider the following case What are the forces acting on the plank? plal ank F= floor W= wall WP E earth PF PE EP EP Physics 121: Lecture 8, Pg 8

Physics 121: Lecture 8, Pg 8 The Free Body Diagram... Consider the following case What are the forces acting on the plank ? P = plank F = floor W = wall E = earth FW,P FP,W FP,F FP,E FF,P FE,P

The Free Body Diagram ■■ Consider the following case What are the forces acting on the plank? Isolate the plank from the rest of the world WP PF P/E Physics 121: Lecture 8, Pg 9

Physics 121: Lecture 8, Pg 9 The Free Body Diagram... Consider the following case What are the forces acting on the plank ? Isolate the plank from the rest of the world. FW,P FP,W FP,F FP,E FF,P FE,P

The Free Body Diagram ■■ The forces acting on the plank should reveal themselves PW PE Physics 121: Lecture 8, Pg 10

Physics 121: Lecture 8, Pg 10 The Free Body Diagram... The forces acting on the plank should reveal themselves... FP,W FP,F FP,E