Come in and turn your lab notebooks into the bin next to file cabinet.

Slides:



Advertisements
Similar presentations
Work, Energy, And Power m Honors Physics Lecture Notes.
Advertisements

Work, Energy and Power. Work = Force component x displacement Work = F x x When the displacement is perpendicular to the force, no work is done. When.
Regents Physics Work and Energy.
Chapter 5 Work and Energy
Notes - Energy A. Work and Energy. What is Energy?  Energy is the ability to produce change in an object or its environment.  Examples of forms of energy:
WORK In order for work to be done, three things are necessary:
WORK In order for work to be done, three things are necessary:
Herriman High Honors Physics Chapter 5 Work, Power and Energy What You Need to Know.
Chapter 5 – Work and Energy If an object is moved by a force and the force and displacement are in the same direction, then work equals the product of.
Work and Energy.
WORK AND ENERGY 1. Work Work as you know it means to do something that takes physical or mental effort But in physics is has a very different meaning.
by the normal force acting on a sliding block?
Mechanics Work and Energy Chapter 6 Work  What is “work”?  Work is done when a force moves an object some distance  The force (or a component of the.
Energy m m Physics 2053 Lecture Notes Energy.
Physics 3.3. Work WWWWork is defined as Force in the direction of motion x the distance moved. WWWWork is also defined as the change in total.
Review and then some…. Work & Energy Conservative, Non-conservative, and non-constant Forces.
Mechanical Energy. Kinetic Energy, E k Kinetic energy is the energy of an object in motion. E k = ½ mv 2 Where E k is the kinetic energy measured in J.
Work and Energy. Work a force that causes a displacement of an object does work on the object W = Fdnewtons times meters (N·m) or joules (J)
1 Work When a force moves something, work is done. Whenever work is done, energy is changed into a different form. Chemical energy → Kinetic energy.
Energy 4 – Elastic Energy Mr. Jean Physics 11. The plan:  Video clip of the day  Potential Energy  Kinetic Energy  Restoring forces  Hooke’s Law.
Work has a specific definition in physics. Work is done anytime a force is applied through a distance.
Energy and Energy Conservation. Energy Two types of Energy: 1. Kinetic Energy (KE) - energy of an object due to its motion 2. Potential Energy (PE) -
Work, Energy, and Energy Conservation Chapter 5, Sections Pg
Physics 221 Chapter 7 Problem 1... Work for slackers! WORK = Force x Distance W = F. D Units: Nm = J Newton meters = Joules Problem 1 : You push a car.
Work has a specific definition in physics
Lecture 12: Elastic Potential Energy & Energy Conservation.
the time rate of doing work; or the time rate transfer of energy.
WORK A force that causes a displacement of an object does work on the object. W = F d Work is done –if the object the work is done on moves due to the.
Work and Energy. Work… …is the product of the magnitude of displacement times the component of force parallel to the displacement. W = F ‖ d Units: N.
WORK & ENERGY Physics, Chapter 5. Energy & Work What is a definition of energy? Because of the association of energy with work, we begin with a discussion.
Work, Power, Energy. Work Concepts Work (W) ~ product of the force exerted on an object and the distance the object moves in the direction of the force.
 Work  Energy  Kinetic Energy  Potential Energy  Mechanical Energy  Conservation of Mechanical Energy.
Chapter 5 Work and Energy. Mechanical Energy  Mechanical Energy is the energy that an object has due to its motion or its position.  Two kinds of mechanical.
CHAPTER 5 Work and Energy Work: Work:Work done by an agent exerting a constant force is defined as the product of the component of the force in the direction.
Work and Energy Energy. Kinetic Energy Kinetic energy – energy of an object due to its motion Kinetic energy depends on speed and mass Kinetic energy.
Energy Notes Energy is one of the most important concepts in science. An object has energy if it can produce a change in itself or in its surroundings.
Aim: How can we apply work- energy to motion problems? Do Now: In your own words, what does energy mean to you? In your own words, what does energy mean.
Energy Conserved “substance” that quantifies an ability to make changes in other objects The ability to make changes in other objects Shape, temperature,
PHY 102: Lecture 4A 4.1 Work/Energy Review 4.2 Electric Potential Energy.
Simple Harmonic Motion & Elasticity
Simple Harmonic Motion & Elasticity
Work is only done by a force on an
Unit 7: Work, Power, and Mechanical Energy.
Chapter 6 Work and Energy.
Simple Harmonic Motion & Elasticity
Work, Energy & Power AP Physics 1.
Work & Energy w/o Machines
Chapter 6 Work and Energy.
Unit 6 Notes Work, Enery, & Power.
General Physics 101 PHYS Dr. Zyad Ahmed Tawfik
Work Done by a Constant Force
Chapter 8B - Work and Energy
Work, Power and Energy.
Chapter 5 Work and Energy
Inclined Planes.
Chapter 8B - Work and Energy
Unit 7: Work, Power, and Mechanical Energy.
Hooke's Law When a springs is stretched (or compressed), a force is applied through a distance. Thus, work is done. W=Fd. Thus elastic potential energy.
WORK.
Work, Energy & Power AP Physics 1.
General Physics I Work & Energy
ENERGY Energy is ‘something’ that which can be converted into work. When something has energy, it is able to perform work or, in a general sense, to change.
Chapter 6 - Work and Energy
Work, Power, Energy.
Chapter 5 Review.
Work, Power, Energy.
Newton’s Law of Universal Gravitation
Work and Energy Chapter 6 Lesson 1
Work In physics, work is the amount of energy transformed (changed) when a force moves (in the direction of the force)
WORK.
Presentation transcript:

Come in and turn your lab notebooks into the bin next to file cabinet. Work and Energy Come in and turn your lab notebooks into the bin next to file cabinet.

Energy Objects (or systems) can have energy and transfer or transform it. When Energy is transferred, we call it “doing work”. Since energy is conserved, we state that: W = ΔE

Work Work = F d cos (θ) F d F d Work is measured in: Remember: Work energy required to make something move. Angle b/t F and d Force (N) Work = F d cos (θ) Work Energy (J) Distance (m) Use only the magnitude of F and d in the equation. The angle will determine if work is positive or negative. Work is measured in: Newton meters (N *m) Joules (J) F d F d WORK DONE NO WORK

A shopper pushes a shopping cart on a rough surface with a force of 8 A shopper pushes a shopping cart on a rough surface with a force of 8.9 N at an angle of 60° to the left of the negative y- axis. While the cart moves a horizontal distance of 10.0 m, what is the work done by the shopper on the shopping cart? Fa = 8.9 N at an angle of 60° to the left of the negative y- axis Y-axis 8.9 N Θ=60° 10 meters

A 40-N force pulls a 4-kg block a horizontal distance of 8 m A 40-N force pulls a 4-kg block a horizontal distance of 8 m. The rope makes an angle of 350 with the floor and μk = 0.2. What is the work done by each force acting on the block AND what is the NET Work (total work)? x Fa q = 40 N = 8m = 35° 4kg μk= 0.2

Find the Work done by each force Work = F d cos (θ) FN Work = F d cos (θ) Fa =40N WFa = F d cos(θ) 35° WFa = (40) (8) cos(35) FF WFa = 262.13 J Fg = mg WFn = 0 J Each of these forces are perpendicular to the distance (90°), so that the works are zero. (cos 900=0): WFg = d = 8m 0 J WFf = FF d cos(θ) WFf = 3.25 (8) cos(180) We need Ff to find the work done by friction. Remember Ff =μFn WFf = -26 J Fn does not equal Fg because the Fa is at an angle. (Fa is “helping” Fn). To find Fn: Fn + (Fa sin(35)) = Fg Fn = mg - (Fa sin(35)) Fn = 16.26 N y-component of Fa Ff =μFn Ff =(0.2)(16.26) Ff =3.25 N

Work done by each force and the total work WFa = 262.13 J WFn = 0 J WFg = 0 J WFf = -26 J Total work = Wfa + WFn + WFg + WFf Total work = 262.13 + 0 + 0 + (-26) Total work = 236.13 J

Fn + Fa sinθ = Fg Ff = Fa cos θ When Fnet = 0, All forces (and components) are equal (constant velocity / no acceleration) FN Fy Fa Remember, the applied force is at an angle. There is an x and y component. θ° FF Fx Fx = Fa cos θ Fy = Fa sin θ Fg = mg Fn + Fa sinθ = Fg Ff = Fa cos θ

Work as the area under the graph Force vs Position graph Force F Positive work done Position x Negative work done

Graph of Force vs. Displacement The area under the curve is equal to the work done. Force, F F x1 x2 Work = F(x2 - x1) Area Displacement, x

What work is done by a constant force of 40 N moving a block from x = 1 m to x = 4 m? Force, F Displacement, x 1 m 4 m Area Work = F(x2 - x1) Work = (40 N)(4 m - 1 m) Work = 120 J

Mechanical Energy ME is the energy related to an objects motion or position Potential Energy (PE or Ug) Stored energy due to position No PE when object is at h=0 PE =mgh Kinetic Energy (KE or K) Energy in motion No KE if object is at rest KE= ½mv2 Elastic Potential Energy (ePE or Us) Energy stored in springs due to compression or stretching ePE= ½kx2

Kinetic and Potential Energy are EQUAL!! Total PE = Total KE There is height and velocity There is height but no velocity There is velocity Height is 0 P.E. = max K.E. = 0 P.E. = K.E. K.E. = max P.E. = 0

Energy is converted but not lost! Total Energy in this system = 100 J P.E. = 100 J K.E. = 0 P.E. = 50 J K.E. = 50 J K.E. = 100 J P.E. = 0

Elastic Potential Energy ePE is Potential energy stored as a result of deformation of an elastic object, such as the stretching of a spring.

Since we know that energy is conserved, we can make the assumption that: KE = PE = ePE = W ½ mv2 = mgh = ½ kx2 = Fd

The Work-Energy Theorem W = ΔKE Work is equal to the change in Kinetic Energy The Work-Energy Theorem: The work done by a resultant force is equal to the change in kinetic energy that it produces.

Work = ½ mvf2 - ½ mvo2 x F d = - ½ mvo2 Example 1: A 20-g projectile strikes a mud bank, going through a distance of 6 cm before stopping. Find the stopping force F if the entrance velocity is 80 m/s. x F = ? 80 m/s 6 cm Work = ½ mvf2 - ½ mvo2 F d = - ½ mvo2 F (0.06 m) = - ½ (0.02 kg)(80 m/s)2 F (0.06 m) = -64 J F = 1067 N Work to stop bullet = change in K.E. for bullet

Work = F d Work = DK 25 m FF FF = mFN = m mg DK = ½ mvf2 - ½ mvo2 Example 2: A bus slams on brakes to avoid an accident. The tread marks of the tires are 25 m long. If m = 0.7, what was the speed before applying brakes? Work = F d Work = DK 25 m FF FF = mFN = m mg DK = ½ mvf2 - ½ mvo2 Work = -m mg d -½ mvo2 = -mk mg d

Example 3: A 4-kg block slides from rest to the bottom of the 300 inclined plane. Find velocity at bottom. (h = 20 m) h 300 FN mg x

Power Power is defined as the rate at which work is done: Work (J) Force (N) Distance (m) P = ΔE = W = Fd cosθ = Fvcosθ t t t Power (watts) Time (sec) Power is measured in Watts

P = (900 kg)(9.8 m/s2)(4 m/s) cos (0°) v = 4 m/s Power Example: What power is required to lift a 900-kg elevator at a constant speed of 4 m/s? P = F v cos θ= mg v cos θ P = (900 kg)(9.8 m/s2)(4 m/s) cos (0°) P = 35300 W

Hooke’s Law When a spring is stretched, there is a restoring force that is proportional to the displacement. The larger the displacement, the larger the restoring force F x m The spring constant k is a property of the spring given by:

The stretching force is the weight (W = mg) of the 4-kg mass: Example: A 4-kg mass suspended from a spring produces a displacement of 20 cm. What is the spring constant? F 20 cm m The stretching force is the weight (W = mg) of the 4-kg mass: F = (4 kg)(9.8 m/s2) = 39.2 N Now, from Hooke’s law, the force constant k of the spring is: k = = DF Dx 39.2 N 0.2 m k = 196 N/m