Unit 6 Friction Todays Concept Friction UP Mechanics

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Unit 6 Friction Today’s Concept: Friction UP Mechanics Lecture 6, Slide 1

Unit 6 Friction Today’s Concept: Friction UP Mechanics Lecture 6, Slide 1

Midterm 1 Average=102. 1”%” Excellent Job! You can do the problems! Mechanics Lecture 6,

Midterm 1 Average=102. 1”%” Excellent Job! You can do the problems! Mechanics Lecture 6, Slide 2

Unit 5 Homework Two of the problems were for unit 6…. Deadline for unit

Unit 5 Homework Two of the problems were for unit 6…. Deadline for unit 5 Extended until this Thursday @ 11: 30 Pm Mechanics Lecture 6, Slide 3

Video Prelectures/lecture Thoughts Mechanics Lecture 6, Slide 4

Video Prelectures/lecture Thoughts Mechanics Lecture 6, Slide 4

Friction Mechanics Lecture 6, Slide 5

Friction Mechanics Lecture 6, Slide 5

Friction Always opposes the relative motion of two surfaces Mechanics Lecture 6, Slide 6

Friction Always opposes the relative motion of two surfaces Mechanics Lecture 6, Slide 6

Friction Mechanics Lecture 6, Slide 7

Friction Mechanics Lecture 6, Slide 7

Static Friction Mechanics Lecture 6, Slide 8

Static Friction Mechanics Lecture 6, Slide 8

Static Friction Mechanics Lecture 6, Slide 9

Static Friction Mechanics Lecture 6, Slide 9

Static Friction Mechanics Lecture 6, Slide 10

Static Friction Mechanics Lecture 6, Slide 10

Without Friction Mechanics Lecture 6, Slide 11

Without Friction Mechanics Lecture 6, Slide 11

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 12

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 12

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 13

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 13

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 14

Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 14

Block Mechanics Lecture 5, Slide 15

Block Mechanics Lecture 5, Slide 15

Static Friction Starts to Slide Mechanics Lecture 6, Slide 16

Static Friction Starts to Slide Mechanics Lecture 6, Slide 16

Static Friction/Car Skidding Mechanics Lecture 6, Slide 17

Static Friction/Car Skidding Mechanics Lecture 6, Slide 17

Pushing Blocks Mechanics Lecture 5, Slide 18

Pushing Blocks Mechanics Lecture 5, Slide 18

Pushing Blocks Normal force = weight of two blocks Force to accelerate two Blocks

Pushing Blocks Normal force = weight of two blocks Force to accelerate two Blocks with acceleration=a Mechanics Lecture 5, Slide 19

Main Points Mechanics Lecture 6, Slide 20

Main Points Mechanics Lecture 6, Slide 20

Main Points Mechanics Lecture 6, Slide 21

Main Points Mechanics Lecture 6, Slide 21

Check. Point A block slides on a table pulled by a string attached to

Check. Point A block slides on a table pulled by a string attached to a hanging weight. In Case 1 the block slides without friction and in Case 2 there is kinetic friction between the sliding block and the table. m 2 Case 1 (No Friction) m 2 g Case 2 m 1 (With Friction) g m 1 In which case is the tension in the string biggest? A) Case 1 B) Case 2 C) Same 68% got this right on first try Mechanics Lecture 6, Slide 22

m 2 Case 1 (No Friction) g Case 2 m 1 g (With Friction)

m 2 Case 1 (No Friction) g Case 2 m 1 g (With Friction) m 1 In which case is the tension in the string biggest? A) Case 1 B) Case 2 C) Same B) M 1 will not be accelerating as fast in case two than in case one because there is the extra force of friction acting against mass 1. Since the acceleration is smaller in case two, there has to be more of a force acting against gravity, the only other possible force is Tension. Mechanics Lecture 6, Slide 23

Lets work it out A block (m 2) slides on a table pulled by

Lets work it out A block (m 2) slides on a table pulled by a string attached to a mass (m 1) hanging over the side. The coefficient of kinetic friction between the sliding block and the table is k. What is the tension in the string? m 2 g m 1 Mechanics Lecture 6, Slide 24

1) FBD m 2 N f m 2 T g T m 2 g

1) FBD m 2 N f m 2 T g T m 2 g m 1 m 1 g Mechanics Lecture 6, Slide 27

1) FBD 2) SF=ma m 2 N f T m 2 g N =

1) FBD 2) SF=ma m 2 N f T m 2 g N = m 2 g T – m 2 g = m 2 a g m 1 g – T = m 1 a m 1 m 1 g add m 1 g – m 2 g = m 1 a + m 2 a m 1 g – m 2 g a= m 1 + m 2 Mechanics Lecture 6, Slide 28

1) FBD 2) SF=ma m 2 N f m 2 T g T m

1) FBD 2) SF=ma m 2 N f m 2 T g T m 1 m 2 g m 1 g – m 2 g a= m 1 + m 2 m 1 g – T = m 1 a T = m 1 g – m 1 a T is smaller when a is bigger Mechanics Lecture 6, Slide 29

Checkpoint A. B. C. A box sits on the horizontal bed of a moving

Checkpoint A. B. C. A box sits on the horizontal bed of a moving truck. Static friction between the box and the truck keeps the box from sliding around as the truck drives. S a If the truck moves with constant acceleration to the left as shown, which of the following diagrams best describes the static frictional force acting on the box: A B C Mechanics Lecture 6, Slide 30

Check. Point S a If the truck moves with constant accelerating to the left

Check. Point S a If the truck moves with constant accelerating to the left as shown, which of the following diagrams best describes the static frictional force acting on the box: 56% correct A B C A) In order to keep the box from sliding to the back of the truck as it accelerates, the frictional force needs to pull/push the box forward. B) Friction always opposes motion/acceleration. Mechanics Lecture 6, Slide 31

Clicker Question A box of mass M sits on a horizontal table. A horizontal

Clicker Question A box of mass M sits on a horizontal table. A horizontal string having tension T applies a force on the box, but static friction between the box and the table keeps the box from moving. What is the magnitude of the total force acting on the box? T f A) Mg B) m. Mg C) T D) 0 M Since acceleration is zero. Mechanics Lecture 6, Slide 32

Clicker Question A. B. C. A box of mass M sits on a horizontal

Clicker Question A. B. C. A box of mass M sits on a horizontal table. A horizontal string having tension T applies a force on the box, but static friction between the box and the table keeps the box from moving. D. What is the magnitude of the static frictional force acting on the box? T f A) Mg B) m. Mg C) T D) 0 M Since the box is not moving the forces must be equal, otherwise 38% correct there would be an acceleration. Mechanics Lecture 6, Slide 33

Checkpoint A. B. C. 28% got this right on first try Mechanics Lecture 6,

Checkpoint A. B. C. 28% got this right on first try Mechanics Lecture 6, Slide 34

44% got this right on first try Mechanics Lecture 6, Slide 35

44% got this right on first try Mechanics Lecture 6, Slide 35

Checkpoint A. B. C. Mechanics Lecture 6, Slide 36

Checkpoint A. B. C. Mechanics Lecture 6, Slide 36

Mechanics Lecture 6, Slide 37

Mechanics Lecture 6, Slide 37

Mechanics Lecture 6, Slide 38

Mechanics Lecture 6, Slide 38

Mechanics Lecture 6, Slide 39

Mechanics Lecture 6, Slide 39

Mechanics Lecture 6, Slide 40

Mechanics Lecture 6, Slide 40

Mechanics Lecture 6, Slide 41

Mechanics Lecture 6, Slide 41

Mechanics Lecture 6, Slide 42

Mechanics Lecture 6, Slide 42

Mechanics Lecture 6, Slide 43

Mechanics Lecture 6, Slide 43

Mechanics Lecture 6, Slide 44

Mechanics Lecture 6, Slide 44

Microscopic explanation of Friction What is Friction? Why can’t we walk through walls? Basically

Microscopic explanation of Friction What is Friction? Why can’t we walk through walls? Basically the same answer to both questions… Electron clouds of atoms repel (or bond to) each other q q http: //www. virneth. co. uk/top. Friction/friction 0. php http: //astro 1. panet. utoledo. edu/~vkarpov/Static_Friction_nature. pdf Mechanics Lecture 6, Slide 45

Climbing Skins for Touring Skis Mechanics Lecture 6, Slide 46

Climbing Skins for Touring Skis Mechanics Lecture 6, Slide 46

Accelerating Blocks Mechanics Lecture 6, Slide 47

Accelerating Blocks Mechanics Lecture 6, Slide 47

Accelerating Blocks Mechanics Lecture 6, Slide 48

Accelerating Blocks Mechanics Lecture 6, Slide 48

Carnival Ride Mechanics Lecture 6, Slide 49

Carnival Ride Mechanics Lecture 6, Slide 49

Carnival Ride Mechanics Lecture 6, Slide 50

Carnival Ride Mechanics Lecture 6, Slide 50

Accelerating Truck Mechanics Lecture 6, Slide 51

Accelerating Truck Mechanics Lecture 6, Slide 51

Accelerating Truck Mechanics Lecture 6, Slide 52

Accelerating Truck Mechanics Lecture 6, Slide 52

Mass on Incline Mechanics Lecture 6, Slide 53

Mass on Incline Mechanics Lecture 6, Slide 53

Mass on Incline Mechanics Lecture 6, Slide 54

Mass on Incline Mechanics Lecture 6, Slide 54

Mass on Incline Mechanics Lecture 6, Slide 55

Mass on Incline Mechanics Lecture 6, Slide 55

Mass on Incline 2 Mechanics Lecture 6, Slide 56

Mass on Incline 2 Mechanics Lecture 6, Slide 56

Mass on Incline 2 Mechanics Lecture 6, Slide 57

Mass on Incline 2 Mechanics Lecture 6, Slide 57

Mass on Incline 2 Mechanics Lecture 6, Slide 58

Mass on Incline 2 Mechanics Lecture 6, Slide 58

Mass on Incline 2 Mechanics Lecture 6, Slide 59

Mass on Incline 2 Mechanics Lecture 6, Slide 59