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Some physics: Energy, what exactly is it? (some physics) PHYS105: Physics for Decision Makers: Global Energy Crisis PHYS105: Physics for Decision Makers, Eno, F14 1

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Demos J1-21: electrostatic attraction and repulsion I5-02 transformation of mechanical energy into heat C6-02 inclined plane friction block PHYS105: Physics for Decision Makers, Eno, F14 2

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A little physics Force, Energy, Work, Power PHYS105: Physics for Decision Makers, Eno, F14 3 Dont be afraid: it wont be hard

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Warning PHYS105: Physics for Decision Makers, Eno, F14 4 To paraphrase a quote perhaps falsely attributed to George Bernard Shaw Americans and British are one people separated only by a common language Physicists and non-physicists are one people separated only by a common language. Force, Energy, Work, Power

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Forces PHYS105: Physics for Decision Makers, Eno, F14 5 A push or a pull Some force in your day-to-day life Tension in a rope Gravity normal force Friction Electrostatic force

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Fundamental Forces 15 March 2012 6 Particle physicists think of it as this: Matter: Quarks (protons) leptons (electron) Force boson matter Some more force boson

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And we only have four of them 15 March 2012 7 Electricity and Magnetism (QED) photon Strong Force (QCD) gluon Weak Force W&Z bosons http://www.dreamstime.com/powerplant-infrastructure-stock-photo-imagefree242420 gravity

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Everyday forces in terms of fundamental forces PHYS105: Physics for Decision Makers, Eno, F14 8 Some force in your day-to-day life Tension in a rope: electromagnetism normal force: electromagnetism Friction: electromagnetism Electrostatic force: electromagnetism Gravity: gravity What are some other forces you can think of?

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PHYS105: Physics for Decision Makers, Eno, F14 9 Turn in your reactor form If you have a bit of physics phobia, please dont panic during this lecture! There will only be about 5 lectures this semester that have this much physics.

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electromagnetism PHYS105: Physics for Decision Makers, Eno, F14 10 Knowledge and sophistication of theory has evolved with time, but old way of thinking are still useful. Force field. Two charged objects interact via a field, called the electric field. Each charged particle makes a field. When the other enters the field, the other feels a force. Each therefore makes a force on the other (electric force). Magnetic dipoles (such as bar magnets) interact in a similar way via magnetic fields, to create magnetic forces on each other. Useful to think about it this way when thinking of the electricity in our house. Gauss: oscillating electric and magnetic fields (electromagnetic waves) are light. They oscillate because their electric and magnetic fields get bigger and smaller, like the heights of waves in the ocean. Useful when thinking about global warming, since this involves light. Einstein, Planck: light is a particle, not just a wave, and the possible energies it can have are quantized. Photon is the particle of light. Useful when thinking about solar panels. Max Planck: 1858-1947 Carl Gauss: 1777-1855 Albert Einstein: 1879-1955

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Waves PHYS105: Physics for Decision Makers, Eno, F14 11 Have amplitude, wavelength (), and period (T) The wavelength determines how it interacts with matter (including our atmosphere). We will discuss this in more detail later. ColorWavelength (nm) Wavenumber (cm -1 ) Blue400-500157,000 red600-70090,000 infrared1,000,000 - 700 60-90,000 Light can have any wave length The period is related to the wavelength via Where c is the speed of light.

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Photons PHYS105: Physics for Decision Makers, Eno, F14 12 ColorWavelength (nm) Wavenumber (cm -1 ) Energy (eV) Energy (J) Blue400-500157,00034.8x10 -19 red600-70090,00023.2x10 -19 infrared1,000,000 - 700 60-90,000 They may not have any energies. Possible energies are the fundamental energy multiplied by an integer. The fundamental energy is related to the wavelength and a number called Plancks constant. This is related to the particle-ness of the light (photon) in Quantum Mechanics. h is called plancks constant. h=6.6x10 -34 Js

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Force, Work, Energy PHYS105: Physics for Decision Makers, Eno, F14 13 We divide forces into different types (strong, weak, E&M, gravity). We can also divide energy into different types. Roughly, two types of energy: Associated with an objects motion Associated with (certain kinds of) forces acting on the object (between the object and other objects. )

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motion energy PHYS105: Physics for Decision Makers, Eno, F14 14 Some examples, kinetic energy is the energy due to the bulk motion of the object: Moving car A running person A falling rock A particularly important example The random motion of molecules in a material (heat energy) Usually only the energy associated with the bulk motion of the object is called kinetic, while this kind is called thermal.

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Units for energy PHYS105: Physics for Decision Makers, Eno, F14 15 Joule = 1 kg m 2 /s 2 - Metric unit of energy kWh = 1000 Joule/s for one hour = 3,600,000 J = 3.6 MJ calorie = energy to raise temperature of 1 g of water by one degree C calorie = 4.184 J 1 Calorie (food) = 1 kcal = 1,000 calories =is the equivalent energy to a 100w light bulb on for about 7 minutes BTU (British Thermal Unit) = energy to raise temperature of 1 lb of water by one degree F = 1,055 J = 0.25 Kcal 1eV. Energy acquired by an electron when its potential changes by 1V. 1eV = 1.6x10 -19 J Quad (quadrillion BTUs) = 10 15 BTU = 1.054 EJ (E=10 15 )

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KE and Conversion Practice PHYS105: Physics for Decision Makers, Eno, F14 16 A person of mass 60 kg is moving at a speed of 1 m/s. What is their kinetic energy in Joules? What is their kinetic energy in calories?

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Voting cards PHYS105: Physics for Decision Makers, Eno, F14 17 Which particle has a larger kinetic energy 1)One with a mass of 1 kg moving at 2 m/s 2)One with a mass of 2 kg moving at 1 m/s

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Potential Energy PHYS105: Physics for Decision Makers, Eno, F14 18 Potential Energy (PE) comes from forces between objects. Stored in a force field. Think of when you have to apply a force to keep together or pull them apart. Potential energies only happen for forces whose value depends only on the objects position (gravity, electric force). These forces are called conservative force. It does not apply to other forces (especially friction). PE due to gravitational forces between objects PE due to electrical forces between charged objects PE stored in coiled or extended springs PE in chemical bonds of molecules PE in nuclear bonds of nuclei Sometimes these are given specialized names like chemical energy, gravitational potential energy, nuclear energy etc. Some examples:

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Potential Energy PHYS105: Physics for Decision Makers, Eno, F14 19 Potential Energy is related to (certain kinds of) forces, call conservative forces, acting on an object. If there is a force acting on an object, some other object must be causing that force. So potential energies are related to configurations of objects. Sometimes there are simple formulas for the change in PE when the the configuration is changed.

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Potential Energy practice PHYS105: Physics for Decision Makers, Eno, F14 20 5 m A person with a mass of 60 kg climbs stairs so that their height above the ground changes by 5m. What is their change in gravitational potential energy? What if they go down the stairs?

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Conservation of Energy PHYS105: Physics for Decision Makers, Eno, F14 21 Emmy Noether For a closed system, if there are no external forces acting on the system, the total amount of energy in that system can not change. One kind of energy can change to another type of energy. But if you sum all the types of kinetic and potential energy, the sum will always be the same.

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Energy Equivalents PHYS105: Physics for Decision Makers, Eno, F14 22

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Do you have some understanding of what energy is? PHYS105: Physics for Decision Makers, Eno, F14 25

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Energy and Us PHYS105: Physics for Decision Makers, Eno, F14 26 Lets take a quick tour of how the US uses energy

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Which source of energy do we use the most? 1.Coal 2.nuclear 3.Petroleum 4.Natural gas 5.Renewable energy sources (solar, wind,etc) PHYS105: Physics for Decision Makers, Eno, F14 27

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What fraction of our energy usage is in transportation 1.5% 2.25% 3.50% 4.80% PHYS105: Physics for Decision Makers, Eno, F14 28

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Energy by source and use PHYS105: Physics for Decision Makers, Eno, F14 29 http://www.eia.gov/energyexplained/

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Quad: 1% of US consumption/day PHYS105: Physics for Decision Makers, Eno, F14 30

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What is the leading user of energy in our home? PHYS105: Physics for Decision Makers, Eno, F14 31 1.Space Heat 2.Air Conditioning 3.Refrigerator 4.Water heating 5.Lighting 6.Electronics

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Energy in the home PHYS105: Physics for Decision Makers, Eno, F14 32 Space Heat 10% Air Conditioning 16% Related Heat/cool(fans etc.) 5% Refrigerator 14% Other Kitchen appliances 13% Water heating 9% Lighting 9% Electronics 7% Laundry 7% Miscellaneous 10% US residential electrical use

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What is the leading source of electricity in MD? PHYS105: Physics for Decision Makers, Eno, F14 33 1.Coal 2.Nuclear 3.Natural gas 4.Wind 5.solar

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Maryland Energy Supply PHYS105: Physics for Decision Makers, Eno, F14 34 http://www.eia.gov/state/?sid=md MD ranking in energy use per capita: 40!!!

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Work PHYS105: Physics for Decision Makers, Eno, F14 35 Word of warning: if it can be tweeted, it probably is not the full story. A force does work on an object when the force is applied to the object while the objects position changes.

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d PHYS105: Physics for Decision Makers, Eno, F14 36 5 m For this person, portion of path along the direction of the gravitational force is 5 m. Take direction of force. Draw a line. See how much the position changed measured relative to that line.

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Voting cards PHYS105: Physics for Decision Makers, Eno, F14 37

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Work-Energy theorem PHYS105: Physics for Decision Makers, Eno, F14 38 If you calculate the work for all forces applied to an object and sum them up, the result will tell you how much the kinetic energy of the object will change.

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What to remember PHYS105: Physics for Decision Makers, Eno, F14 39 Work, which is the force applied as an object changes position times the distance moved, results in a change of energy for the object. Force is applied to an object, the object changes position -> energy of the object changes.

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PHYS105: Physics for Decision Makers, Eno, F14 40 If energy is conserved, how can there be an energy crisis? Be sure you can answer this question by the first exam.

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Conservation of energy: heat production PHYS105: Physics for Decision Makers, Eno, F14 41 The answer will be related to this slide. Demo i5-02

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Friction PHYS105: Physics for Decision Makers, Eno, F14 42 Two types of Friction Static: between two surface that are not sliding Kinetic: between two surfaces moving with respect to each other Static Friction is larger Demo c6-02 Friction is everywhere!!! Can you give me examples of friction?

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Friction microscopic view PHYS105: Physics for Decision Makers, Eno, F14 43 Molecules interact via residual electrostatic forces. Friction is the sticking and unsticking of modules (kind of like Velcro) Depends on the roughness Much of the work done by friction turns into random motion of molecules (heat)

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Voting cards PHYS105: Physics for Decision Makers, Eno, F14 44 When I walk across this stage, is the gravitational force doing work? 1)Yes 2)No

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PHYS105: Physics for Decision Makers, Eno, F14 45 Is there any friction involved? 1)Yes 2)no

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PHYS105: Physics for Decision Makers, Eno, F14 46 Is it static or sliding 1)Static 2)sliding

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Power PHYS105: Physics for Decision Makers, Eno, F14 47 Sometimes we care about the total amount of energy we use. Sometimes we care about the rate at which we use energy. Sometimes we care about both. Special name for rate of energy use: Power

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Energy and Power PHYS105: Physics for Decision Makers, Eno, F14 48

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Person Power PHYS105: Physics for Decision Makers, Eno, F14 49 A typical person can do work at a rate of about 100 Watts (J/s) Humans burn energy at a rate of about 1.6x10 13 Watts. World population is about 6x10 9 people. The US burns energy at a rate of 3.3x10 12 Watts. The US population is 3.2x10 8 people.

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Voting cards PHYS105: Physics for Decision Makers, Eno, F14 50 kW-hr is a unit of: 1)Force 2)Energy 3)Work 4)Power 5)None of the above

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Force, Energy, Work Power PHYS105: Physics for Decision Makers, Eno, F14 51 Force, Energy, Work, Power Discuss with your neighbors what each exactly is, and why they are not the same thing.

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Work and potential energy PHYS105: Physics for Decision Makers, Eno, F14 52 Near the surface of the earth (dont try this if you are an astronaut!) Change in potential energy when you lift an object a height h? The potential energy for a conservative force is the negative of the work done by that force when the object is moved.

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Work-Energy theorem PHYS105: Physics for Decision Makers, Eno, F14 53 If you calculate the work for all forces applied to an object and sum them up, the result will tell you how much the kinetic energy of the object will change. If we divide the works into those due to conservative and nonconservative forces, and remembering that W conservative =-PE

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Conservation of Energy PHYS105: Physics for Decision Makers, Eno, F14 54 If work causes energy to change, it stands to reason that, if there are no external forces, the total amount of energy is constant. However, it can change form due to internal forces. Emmy Noether Consider the earth and a person holding a ball as a object. Neglect any forces from the outside universe (the sun for example). Then the total energy in this object is fixed. If the person lets go of the ball, the potential energy of the ball turns into exactly the same amount of other kinds of energy (velocity of the ball plus a small additional heat energy in the ball and surrounding air) Consider the earth (with a mountain on it) and a person at the base of the mountain. When the person climbs a mountain, some of the chemical energy stored in her body becomes their gravitational potential energy (and maybe some heat in them and the air and earth around them).

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What you should have learned PHYS105: Physics for Decision Makers, Eno, F14 56 Be able to define force, energy, work, power and explain the relationship between them. Given Chart A below, convert energies given in one unit to another unit Given a power and an amount of time, be able to calculate the amount of energy used. Define and give examples of kinetic and potential energy Know the amount of power a typical person can produce Know the amount of power currently produced in the world Know the population of the world (to one significant digit) Explain why understanding the electromagnetic force is so important when considering world energy use Know the wave lengths of visible light (blue-red). Know the wavelengths of infrared light. Given Plancks constant and the wavelength of a color of light, calculate the energy of a single photon. Know the formula for the change in gravitational potential energy when the distance that object is above the ground is changed. Do simple calculations using this formula. Explain what physicists mean when they say conservation of energy Know the fraction of US energy use that comes from petroleum, from natural gas, and from coal. Know the fraction of US energy use that is used for transportation and for electric power generation. Explain the difference between static and kinetic friction and recognize when each is occurring.