Unit 6 Friction Todays Concept Friction UP Mechanics
- Slides: 57
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, Slide 2
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
Friction Mechanics Lecture 6, Slide 5
Friction Always opposes the relative motion of two surfaces Mechanics Lecture 6, Slide 6
Friction Mechanics Lecture 6, Slide 7
Static Friction Mechanics Lecture 6, Slide 8
Static Friction Mechanics Lecture 6, Slide 9
Static Friction Mechanics Lecture 6, Slide 10
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 13
Friction Note that we have rotated the coordinate system!!! Mechanics Lecture 6, Slide 14
Block Mechanics Lecture 5, Slide 15
Static Friction Starts to Slide Mechanics Lecture 6, Slide 16
Static Friction/Car Skidding Mechanics Lecture 6, Slide 17
Pushing Blocks Mechanics Lecture 5, Slide 18
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 21
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 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 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 m 1 m 1 g Mechanics Lecture 6, Slide 27
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 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 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 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 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 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, Slide 34
44% got this right on first try Mechanics Lecture 6, Slide 35
Checkpoint A. B. C. Mechanics Lecture 6, Slide 36
Mechanics Lecture 6, Slide 37
Mechanics Lecture 6, Slide 38
Mechanics Lecture 6, Slide 39
Mechanics Lecture 6, Slide 40
Mechanics Lecture 6, Slide 41
Mechanics Lecture 6, Slide 42
Mechanics Lecture 6, Slide 43
Mechanics Lecture 6, Slide 44
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
Accelerating Blocks Mechanics Lecture 6, Slide 47
Accelerating Blocks Mechanics Lecture 6, Slide 48
Carnival Ride Mechanics Lecture 6, Slide 49
Carnival Ride Mechanics Lecture 6, Slide 50
Accelerating Truck Mechanics Lecture 6, Slide 51
Accelerating Truck Mechanics Lecture 6, Slide 52
Mass on Incline Mechanics Lecture 6, Slide 53
Mass on Incline Mechanics Lecture 6, Slide 54
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 57
Mass on Incline 2 Mechanics Lecture 6, Slide 58
Mass on Incline 2 Mechanics Lecture 6, Slide 59
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