Aim: How can we calculate static and kinetic friction? A 3.5 kilogram box is being pulled to the right with a force of 15 newtons. The box is moving at.

Slides:



Advertisements
Similar presentations
A 100kg wooden box is standing on a wooden floor
Advertisements

Newton’s Laws of Motion and Free Body Analysis
Unbalanced Forces.
Friction. Friction - the force needed to drag one object across another. (at a constant velocity) Depends on: How hard the surfaces are held together.
Aim: More friction Do Now:
Static and Kinetic Friction
Newton’s 3rd Law of Motion By: Heather Britton. Newton’s 3rd Law of Motion Newton’s 3rd Law of Motion states Whenever one object exerts a force on a second.
Newton’s 3rd Law: More Practice
Friction Friction is the force that opposes the motion between two surfaces that touch. Friction forces are parallel to the contact surface and opposite.
Friction and the Coefficients of Friction
Friction -A force which opposes motion. There are two types of friction: 1.Static Friction – the force exerted on a stationary object in order to get the.
What is a force? How does friction affect motion?
Friction is a force that opposes the motion between two surfaces that are in contact  is a force that opposes the motion between two surfaces that are.
Friction.
Friction There are many forms of friction. This lesson introduces the force laws for static friction, kinetic friction, and rolling friction. Students.
Static and Kinetic Friction
Forces Mass, Weight, and Friction. Weight Weight: force of gravity on an object - on Earth your weight is a direct measure of the planet’s force pulling.
Friction. Newton’s Second Law W = mg W = mg Gives us F = ma Gives us F = ma.
Unit 2 1D Vectors & Newton’s Laws of Motion. A. Vectors and Scalars.
Friction, air resistance
FRICTION!.
NEWTON’S SECOND LAW.
Aim: How can we define friction? Do Now: A 20 kg object is being pulled across a table at a constant velocity with a force of 58.8 N. Draw a free-body.
Friction And Forces in Two Dimensions. Review A force is a push or pull. A force is a push or pull. Newton’s 3 Laws of Motion: Newton’s 3 Laws of Motion:
1 4 Topics force and net force inertia and 1 st law acceleration and 2 nd law g notation force pairs and 3 rd law force diagrams equilibrium friction.
Newton’s Laws of Motion
Week.  Student will:  Incorporate Force of Friction into calculation  Static Friction  Kinetic Friction.
Forces and Free-Body Diagrams
4-4: Everyday Forces Objectives: Explain the difference between mass and weight Find the direction and magnitude of the normal force Describe air resistance.
Friction. A World Without Friction… watch?v=VUfqjSeeZnghttps:// watch?v=VUfqjSeeZng.
Lecture 9: Forces & Laws of Motion. Questions of Yesterday You must apply a force F to push your physics book across your desk at a constant velocity.
Bellwork Pick up a free-body diagram sheet and begin working on it.
Friction Ffriction = μFNormal.
Friction What is friction?. Answer Me!!! Think of two factors that affect friction.
Where the Rubber Meets the Road
Review Force, Friction, Motion, Power and Work.  In science, a force is a push or a pull.  All forces have two properties:  Direction and Size  A.
Unit 2 1D Vectors & Newton’s Laws of Motion. A. Vectors and Scalars.
Friction. Consider An Object Coming to Rest Aristotle’s idea: Rest is the “natural state” of terrestrial objects Newton’s view: A moving object comes.
Friction & Applying Newton’s 2 nd Law Chapter 6.2 System.
SECTION 5.2 FRICTION Define the friction force.
The tendency of objects to resist change in their state of motion is called inertia  Inertia is measured quantitatively by the object's mass.  Objects.
Everyday Forces Weight Normal Force Friction Force.
Basic Information: Force: A push or pull on an object Forces can cause an object to: Speed up Slow down Change direction Basically, Forces can cause an.
Everyday Forces Chapter 4 – Section 4 St. Augustine Preparatory School October 13, 2016.
 Friction – force that opposes motion  Caused by microscopic irregularities of a surface  The friction force is the force exerted by a surface as an.
Force of Friction Friction acts to oppose motion between two surfaces in contact Friction acts to oppose motion between two surfaces in contact F f F f.
Lesson 4.4 Everyday Forces Essential Question: What are some of the everyday forces?
Friction is a type of force between two touching surfaces.
Test #3 Notes Forces and the Laws of Motion Circular Motion and Gravitation Chapters 4 and 7.
Mu of the Shoe Chapter 2, Activity 6. Friction What is friction? –A–An interaction between a moving object and its environment Produces heat and loss.
Friction the force exerted by a surface that opposes the motion of an object moving (or trying to move) across it.
Do Now: A boy pushes a 5Kg box across a floor with a force of 40N. If the force of friction is 10N find the acceleration of the box. (Draw a force diagram)
FRICTION Aim: How do different surfaces affect the amount of friction?
Warm Up The coefficient of friction is 0.17, and the object is accelerating at 3m/s2 to the right, what is the force in each direction and what is the.
Chapter 12 Review a d 13 kg b c A box is accelerated to the right across the smooth surface of a table with an applied force of 40 Newtons. The table surface.
Do Now: What are the units for the coefficient of friction and it’s symbol? What affects the coefficient of friction? Draw the FBD for a block being pulled.
Unbalanced Forces Part #1.
2. What happens if the force is increased?
Friction.
Newton’s Laws Acceleration
Free Body diagrams and problem solving
Friction.
Static and Kinetic Friction
Newton’s Laws of Motion Chapters 2,3,6,7
Friction and Normal Force
Force of Friction.
Aim: How do we explain the force of friction?
Static and Kinetic Friction
Friction & Applying Newton’s 2nd Law
Friction Ff =  . Fnorm “” is the coefficient of friction…it represents the types of surfaces that are in contact with each other.
Presentation transcript:

Aim: How can we calculate static and kinetic friction? A 3.5 kilogram box is being pulled to the right with a force of 15 newtons. The box is moving at constant velocity. A 3.5 kilogram box is being pulled to the right with a force of 15 newtons. The box is moving at constant velocity. A) Sketch a free body diagram. A) Sketch a free body diagram. B) Identify the net force. B) Identify the net force. C) Determine the frictional force. C) Determine the frictional force.

Activity Slide block without text book on table. Slide block without text book on table. Slide block with text book on table. Slide block with text book on table. Slide block on sand paper with text book. Slide block on sand paper with text book.

Friction A force that causes surfaces to STICK TOGETHER At the MICROSCOPIC level, most surfaces are very BUMPY and IRREGULAR Ways to minimize friction SMOOTH SURFACESLUBRICATION

Friction

How can we describe frictional force? FRICTION How can we determine the direction of the frictional force? How can we determine the direction of the frictional force? Acts opposite to direction of motion. Acts opposite to direction of motion. Two types of friction: Two types of friction: 1. Static friction (force needed to put an object in motion) 1. Static friction (force needed to put an object in motion) 2. Kinetic friction (force needed to keep an object moving at constant speed). 2. Kinetic friction (force needed to keep an object moving at constant speed).

Coefficient of Friction (μ) How much materials STICK TOGETHER How much materials STICK TOGETHER DIMENSIONLESS (no units) DIMENSIONLESS (no units) The HIGHER the coefficient, the MORE two surfaces STICK TOGETHER The HIGHER the coefficient, the MORE two surfaces STICK TOGETHER LOWER if surfaces are SLIDING past each other LOWER if surfaces are SLIDING past each other

What else does frictional force depend on…… 1. Coefficient of friction. 1. Coefficient of friction. 2. The normal force of the object to be moved. 2. The normal force of the object to be moved.

Coefficients of Friction [Examine table of coefficients of friction in reference table] [Examine table of coefficients of friction in reference table] Coefficient of friction relates to the roughness of the two surfaces in contact. Coefficient of friction relates to the roughness of the two surfaces in contact. Note: Coefficient of friction has no units. Note: Coefficient of friction has no units. Note: Static friction is always greater than kinetic friction between two surfaces – it is harder to start something moving than to keep it moving. Note: Static friction is always greater than kinetic friction between two surfaces – it is harder to start something moving than to keep it moving.

Friction formula: Friction formula: F f = µF N, where F f = µF N, where F f = force of friction F f = force of friction µ = “coefficient of friction” and µ = “coefficient of friction” and F N = “normal force” acting on the object to be moved. F N = “normal force” acting on the object to be moved. F g =mg F N =mg Only for Horizontal surfaces F g = F N

Does friction depend on area? Slide the block on your table. Read the scale (Newtons). Slide the block on your table. Read the scale (Newtons). The force of friction does not depend on the surface area of the surfaces. The force of friction does not depend on the surface area of the surfaces.

Example: How much force must be applied to begin moving a stationary 5 kg wooden box on a wooden floor? How much force must be applied to begin moving a stationary 5 kg wooden box on a wooden floor? F f = µF N = µmg F f = µF N = µmg = (0.42) (5 kg) (9.8 m/s 2 ) = (0.42) (5 kg) (9.8 m/s 2 ) = 20.6 Newtons = 20.6 Newtons

Aim: How can we solve for kinetic and static friction? 1) Explain the difference between static and kinetic friction. 1) Explain the difference between static and kinetic friction. 2) A student pushes a stationary 500 newton steel box on a level steel surface. The student exerts a 15 newton horizontal force on the box. 2) A student pushes a stationary 500 newton steel box on a level steel surface. The student exerts a 15 newton horizontal force on the box. A) Does the box move? What is the static frictional force? A) Does the box move? What is the static frictional force? B) Determine the minimum amount of force needed to move the box. B) Determine the minimum amount of force needed to move the box.

Example 2: How much force does it take to keep a 1000 kg car moving at constant speed on a dry asphalt road? How much force does it take to keep a 1000 kg car moving at constant speed on a dry asphalt road? F f = µF N = µmg F f = µF N = µmg = (0.67) (1000 kg) (9.8 m/s 2 ) = (0.67) (1000 kg) (9.8 m/s 2 ) = 6,566 Newtons = 6,566 Newtons

The coefficient of kinetic friction between a 640.-newton crate and a level warehouse floor is Calculate the magnitude of the horizontal force required to move the crate across the floor at constant speed.

Example 3: Calculate the coefficient of friction between a 60 newton block of wood and sandpaper if it takes 12 Newtons of force to move the wood on the sandpaper? Calculate the coefficient of friction between a 60 newton block of wood and sandpaper if it takes 12 Newtons of force to move the wood on the sandpaper? F f = µF N F f = µF N

Example 4: What is the coefficient of friction of a tire on a level road if an 1,100kg car decelerates at a rate of 3 m/s 2 once the driver takes her foot off the gas pedal? What is the coefficient of friction of a tire on a level road if an 1,100kg car decelerates at a rate of 3 m/s 2 once the driver takes her foot off the gas pedal?

Summary Describe friction Describe friction How are static and kinetic friction similar?...how are they different? How are static and kinetic friction similar?...how are they different? Describe what frictional force depends on. Describe what frictional force depends on.