© Houghton Mifflin Harcourt Publishing Company Preview Objectives Definition of Work Chapter 5 Section 1 Work.

Slides:



Advertisements
Similar presentations
Work & Energy Physics, Chapter 5.
Advertisements

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Work and Energy Chapter 5 Table of Contents Section 1 Work Section.
Chapter 5 – WORK and ENERGY. 5.2 MECHANICAL ENERGY.
UNIT 4 Work, Energy, and Power. By what factor does the kinetic energy of a car change when its speed is tripled? 1) no change at all 2) factor of 3 3)
Work.  The product of the magnitudes of the component of a force along the direction of displacement and the displacement.  Units-Force x Length  N.
Chapter 2 Preview Objectives Changes in Velocity
Chapter 5 Work and Energy
Chapter 5 Work and Energy
Chapter 4 Preview Objectives Force Force Diagrams
Work and Energy Section 1 © Houghton Mifflin Harcourt Publishing Company What do you think? List five examples of things you have done in the last year.
Bellringer 10/25 A 95 kg clock initially at rest on a horizontal floor requires a 650 N horizontal force to set it in motion. After the clock is in motion,
Herriman High Honors Physics Chapter 5 Work, Power and Energy What You Need to Know.
Objectives Recognize the difference between the scientific and ordinary definitions of work. Define work by relating it to force and displacement. Identify.
Chapter 5 Work and Energy. Force, displacement  WORK.
Chapter 6 Preview Objectives Linear Momentum
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.
© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 4 Section 1 Changes in Motion TEKS 4E develop and interpret free-body.
Chapter 5 Work and Energy. Review  x = v i  t + ½ a  t 2  x = ½ (v i + v f )  t v f = v i + a  t v f 2 = v i 2 + 2a  x.
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Work Chapter 5 Definition of Work Work is done on an object.
Preview Objectives Definition of Work Chapter 5 Section 1 Work.
Section 5–2: Energy Physics Coach Kelsoe Pages 164 – 172.
Work and Energy Section 1 © Houghton Mifflin Harcourt Publishing Company Preview Section 1 WorkWork Section 2 EnergyEnergy Section 3 Conservation of EnergyConservation.
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)
© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 2 Section 1 Displacement and Velocity TEKS 4A generate and interpret.
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
Work has a specific definition in physics
Work and Energy Physics Mr. Day. Work F Work - the product of the magnitudes of the component of a force along the direction of displacement and the displacement.
Chapter 5 - Physics Work and Energy. Section 1 objectives  Recognize the difference between the scientific and ordinary definition of work.  Define.
© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 6 Section 1 Momentum and Impulse TEKS 6C calculate the mechanical energy.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives One Dimensional Motion Displacement Average Velocity Velocity and Speed Interpreting.
© Houghton Mifflin Harcourt Publishing Company Chapter 5 Definition of Work Work is done on an object when a force causes a displacement of the object.
5-3: Conservation of Energy Objectives: Identify situations in which conservation of mechanical energy is valid Recognize the forms that conserved energy.
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.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives Definition of Work Chapter 5 Section 1 Work.
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 and Energy Physics 1. The Purpose of a Force  The application of a force on an object is done with the goal of changing the motion of the object.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives Force Force Diagrams Chapter 4 Section 1 Changes in Motion.
Chapter 7 Centripetal Acceleration Ac= Vt2 / R Centripetal Force
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 and Energy. Section Objectives: Define work by relating it to force and displacement. Identify where work is being performed in a variety of situations.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives Linear Momentum Chapter 6 Section 1 Momentum and Impulse.
Physics Section 5.2 Define and apply forms of mechanical energy. Energy is the ability to do work. Kinetic energy is the energy of an object due its motion.
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Work Chapter 5 Definition of Work Work is done on an object.
Section 5–3: Conservation of Energy Physics Coach Kelsoe Pages 173 – 178.
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Work Chapter 5 Definition of Work Work is done on an object.
The Physics Energy. Objectives Identify several forms of energy. Calculate kinetic energy for an object. Apply the work–kinetic energy theorem to solve.
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Work and Energy Chapter 5 Table of Contents Section 1 Work Section.
Work and Energy Work.
Chapter 5 Section 1 Work Objectives
Chapter 5 Section 1 Work Preview Objectives Definition of Work.
Chapter 5 Work and Energy.
Chapter 5 Section 1 Work Preview Objectives Definition of Work.
Chapter 5 Section 1 Work Preview Objectives Definition of Work.
Work and Energy Physics Chapter 5.
Section 3 Conservation of Energy
Chapter 5 Work and Energy
Chapter 5 Definition of Work 5.1 Work
Standardized Test Prep
WORK And NRG.
How to Use This Presentation
Essential Question: How do you calculate potential and kinetic energy?
Chapter 5 Pgs
Review of Work and Power
Chapter 5 Definition of Work
Chapter 5 Table of Contents Section 1 Work Section 2 Energy
Work and Energy.
Unit 5 ENERGY.
Potential & Kinetic energy
Presentation transcript:

© Houghton Mifflin Harcourt Publishing Company Preview Objectives Definition of Work Chapter 5 Section 1 Work

© Houghton Mifflin Harcourt Publishing Company Section 1 Work Chapter 5 Objectives Recognize the difference between the scientific and ordinary definitions of work. Define work by relating it to force and displacement. Identify where work is being performed in a variety of situations. Calculate the net work done when many forces are applied to an object.

© Houghton Mifflin Harcourt Publishing Company Chapter 5 Definition of Work Work is done on an object when a force causes a displacement of the object. Work is done only when components of a force are parallel to a displacement. Section 1 Work

© Houghton Mifflin Harcourt Publishing Company Chapter 5 Definition of Work Section 1 Work

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 1 Work Sign Conventions for Work

© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 5 Section 2 Energy TEKS 3F express and interpret relationships symbolically in accordance with accepted theories to make predictions and solve problems mathematically, including problems requiring proportional reasoning and graphical vector addition 6A investigate and calculate quantities using the work-energy theorem in various situations 6B investigate examples of kinetic and potential energy and their transformations

© Houghton Mifflin Harcourt Publishing Company Preview Objectives Kinetic Energy Sample Problem Chapter 5 Section 2 Energy

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Objectives Identify several forms of energy. Calculate kinetic energy for an object. Apply the work–kinetic energy theorem to solve problems. Distinguish between kinetic and potential energy. Classify different types of potential energy. Calculate the potential energy associated with an object’s position.

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Kinetic Energy The energy of an object that is due to the object’s motion is called kinetic energy. Kinetic energy depends on speed and mass.

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 2 Energy Kinetic Energy

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Kinetic Energy, continued Work-Kinetic Energy Theorem –The net work done by all the forces acting on an object is equal to the change in the object’s kinetic energy. The net work done on a body equals its change in kinetic energy. W net = ∆KE net work = change in kinetic energy

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 2 Energy Work-Kinetic Energy Theorem

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem Work-Kinetic Energy Theorem On a frozen pond, a person kicks a 10.0 kg sled, giving it an initial speed of 2.2 m/s. How far does the sled move if the coefficient of kinetic friction between the sled and the ice is 0.10?

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 1. Define Given: m = 10.0 kg v i = 2.2 m/s v f = 0 m/s µ k = 0.10 Unknown: d = ?

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 2. Plan Choose an equation or situation: This problem can be solved using the definition of work and the work-kinetic energy theorem. W net = F net dcos  The net work done on the sled is provided by the force of kinetic friction. W net = F k dcos  = µ k mgdcos 

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 2. Plan, continued The force of kinetic friction is in the direction opposite d,  = 180°. Because the sled comes to rest, the final kinetic energy is zero. W net = ∆KE = KE f - KE i = –(1/2)mv i 2 Use the work-kinetic energy theorem, and solve for d.

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 3. Calculate Substitute values into the equation:

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Work-Kinetic Energy Theorem 4. Evaluate According to Newton’s second law, the acceleration of the sled is about -1 m/s 2 and the time it takes the sled to stop is about 2 s. Thus, the distance the sled traveled in the given amount of time should be less than the distance it would have traveled in the absence of friction. 2.5 m < (2.2 m/s)(2 s) = 4.4 m

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Potential Energy Potential Energy is the energy associated with an object because of the position, shape, or condition of the object. Gravitational potential energy is the potential energy stored in the gravitational fields of interacting bodies. Gravitational potential energy depends on height from a zero level. PE g = mgh gravitational PE = mass  free-fall acceleration  height

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 2 Energy Potential Energy

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Potential Energy, continued Elastic potential energy is the energy available for use when a deformed elastic object returns to its original configuration. The symbol k is called the spring constant, a parameter that measures the spring’s resistance to being compressed or stretched.

© Houghton Mifflin Harcourt Publishing Company Chapter 5 Elastic Potential Energy Section 2 Energy

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 2 Energy Spring Constant

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem Potential Energy A 70.0 kg stuntman is attached to a bungee cord with an unstretched length of 15.0 m. He jumps off a bridge spanning a river from a height of 50.0 m. When he finally stops, the cord has a stretched length of 44.0 m. Treat the stuntman as a point mass, and disregard the weight of the bungee cord. Assuming the spring constant of the bungee cord is 71.8 N/m, what is the total potential energy relative to the water when the man stops falling?

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 1. Define Given:m = 70.0 kg k = 71.8 N/m g = 9.81 m/s 2 h = 50.0 m – 44.0 m = 6.0 m x = 44.0 m – 15.0 m = 29.0 m PE = 0 J at river level Unknown:PE tot = ?

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 2. Plan Choose an equation or situation: The zero level for gravitational potential energy is chosen to be at the surface of the water. The total potential energy is the sum of the gravitational and elastic potential energy.

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 3. Calculate Substitute the values into the equations and solve:

© Houghton Mifflin Harcourt Publishing Company Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 4. Evaluate One way to evaluate the answer is to make an order-of-magnitude estimate. The gravitational potential energy is on the order of 10 2 kg  10 m/s 2  10 m = 10 4 J. The elastic potential energy is on the order of 1  10 2 N/m  10 2 m 2 = 10 4 J. Thus, the total potential energy should be on the order of 2  10 4 J. This number is close to the actual answer.

© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 5 Section 3 Conservation of Energy TEKS 6C calculate the mechanical energy of, power generated within, impulse applied to, and momentum of a physical system 6D demonstrate and apply the laws of conservation of energy and conservation of momentum in one dimension

© Houghton Mifflin Harcourt Publishing Company Preview Objectives Conserved Quantities Mechanical Energy Sample Problem Chapter 5 Section 3 Conservation of Energy

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Objectives Identify situations in which conservation of mechanical energy is valid. Recognize the forms that conserved energy can take. Solve problems using conservation of mechanical energy.

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Conserved Quantities When we say that something is conserved, we mean that it remains constant.

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Mechanical Energy Mechanical energy is the sum of kinetic energy and all forms of potential energy associated with an object or group of objects. ME = KE + ∑PE Mechanical energy is often conserved. ME i = ME f initial mechanical energy = final mechanical energy (in the absence of friction)

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 3 Conservation of Energy Conservation of Mechanical Energy

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem Conservation of Mechanical Energy Starting from rest, a child zooms down a frictionless slide from an initial height of 3.00 m. What is her speed at the bottom of the slide? Assume she has a mass of 25.0 kg.

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem, continued Conservation of Mechanical Energy 1. Define Given: h = h i = 3.00 m m = 25.0 kg v i = 0.0 m/s h f = 0 m Unknown: v f = ?

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem, continued Conservation of Mechanical Energy 2. Plan Choose an equation or situation: The slide is frictionless, so mechanical energy is conserved. Kinetic energy and gravitational potential energy are the only forms of energy present.

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem, continued Conservation of Mechanical Energy 2. Plan, continued The zero level chosen for gravitational potential energy is the bottom of the slide. Because the child ends at the zero level, the final gravitational potential energy is zero. PE g,f = 0

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem, continued Conservation of Mechanical Energy 2. Plan, continued The initial gravitational potential energy at the top of the slide is PE g,i = mgh i = mgh Because the child starts at rest, the initial kinetic energy at the top is zero. KE i = 0 Therefore, the final kinetic energy is as follows:

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Conservation of Mechanical Energy 3. Calculate Substitute values into the equations: PE g,i = (25.0 kg)(9.81 m/s 2 )(3.00 m) = 736 J KE f = (1/2)(25.0 kg)v f 2 Now use the calculated quantities to evaluate the final velocity. ME i = ME f PE i + KE i = PE f + KE f 736 J + 0 J = 0 J + (0.500)(25.0 kg)v f 2 v f = 7.67 m/s Sample Problem, continued

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Sample Problem, continued Conservation of Mechanical Energy 4. Evaluate The expression for the square of the final speed can be written as follows: Notice that the masses cancel, so the final speed does not depend on the mass of the child. This result makes sense because the acceleration of an object due to gravity does not depend on the mass of the object.

© Houghton Mifflin Harcourt Publishing Company Section 3 Conservation of Energy Chapter 5 Mechanical Energy, continued Mechanical Energy is not conserved in the presence of friction. As a sanding block slides on a piece of wood, energy (in the form of heat) is dissipated into the block and surface.

© Houghton Mifflin Harcourt Publishing Company The student is expected to: Chapter 5 Section 4 Power TEKS 6C calculate the mechanical energy of, power generated within, impulse applied to, and momentum of a physical system

© Houghton Mifflin Harcourt Publishing Company Preview Objectives Rate of Energy Transfer Chapter 5 Section 4 Power

© Houghton Mifflin Harcourt Publishing Company Section 4 Power Chapter 5 Objectives Relate the concepts of energy, time, and power. Calculate power in two different ways. Explain the effect of machines on work and power.

© Houghton Mifflin Harcourt Publishing Company Section 4 Power Chapter 5 Rate of Energy Transfer Power is a quantity that measures the rate at which work is done or energy is transformed. P = W/∆t power = work ÷ time interval An alternate equation for power in terms of force and speed is P = Fv power = force  speed

© Houghton Mifflin Harcourt Publishing Company Click below to watch the Visual Concept. Visual Concept Chapter 5 Section 4 Power Power