Ch6+LambertM

=**Energy Conservation** = toc

Work, Energy, and Power: Lesson 1a
**1) Definition and Mathematics of Work**

Survey Question Read Recite Review
 * 1) What is the definition of work and what is required for work to occur?
 * 2) How can work be expressed mathematically?
 * 3) What is the meaning of negative work?
 * 4) What are the units of work?
 * 1) **Work**: when a force acts upon and object to cause a displacement of the object. In order for work to occur there must be force, displacement, and cause.
 * 2) **Mathematics:** [[image:http://www.physicsclassroom.com/Class/energy/u5l1a1.gif width="116" height="10" align="bottom"]](F=force, d=displacement, theta=the angle between the force and the displacement vector)
 * 3) **Negative work**: when a force acts upon a moving object to hinder displacement
 * 4) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**Units**: 1 joule (=1 Newton*1 meter)

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 1.1em;">Work, Energy, and Power: Lesson 2a
<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 14px;">Internal vs. External Forces <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The force of gravity, electrical forces, and magnetic forces were examples of forces that could exist between two objects even when they are not physically touching.Certain forces when present and involved in doing work on objects will change the total mechanical energy of the object. there are other types of forces that can transform the energy of an object from potential energy to kinetic energy (or vice versa)called internal forces and external forces.

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**External forces** include the applied force, normal force, tension force, friction force, and air resistance force. **Internal forces** include the gravity forces, magnetic force, electrical force, and spring force. <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">When net work is done upon an object by an external force, the total mechanical energy (KE+PE) of that object is changed. If the work is//positive work//, then the object will gain energy. If the work is //negative work//, then the object will lose energy. The gain or loss in energy can be in the form of potential energy, kinetic energy, or both. The work that is done will be __equal__ to the change in mechanical energy of the object. Because external forces are capable of changing the total mechanical energy of an object, they are sometimes referred to as **nonconservative forces**.

<span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">When the only type of force doing net work upon an object is an internal force (ie- gravitational and spring forces), the TME of that object remains constant. In such cases, the object's energy changes form. For example, as an object is "forced" from a high elevation to a lower elevation by gravity, some of the potential energy of that object is transformed into kinetic energy. Yet, the sum of the kinetic and potential energies remains constant. This is referred to as energy conservation. When the only forces doing work are internal forces, energy changes forms - from kinetic to potential (or vice versa); yet the total amount of mechanical is conserved. Because internal forces are capable of changing the form of energy without changing the total amount of mechanical energy, they are sometimes referred to as**conservative forces**. <span style="color: #000000; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Exercises:
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">A ball falls from a height of 2 meters in the absence of air resistance.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">PE --> KE
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">A skier glides from location A to location B across a friction free ice.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">PE --> KE
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">A baseball is traveling upward towards a man in the bleachers.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">KE --> PE
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">A bungee cord begins to exert an upward force upon a falling bungee jumper.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">KE --> PE
 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The spring of a dart gun exerts a force on a dart as it is launched from an initial rest position.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">PE --> KE

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">** Why Do My Parents Tell Me to Turn off the Lights? :) **
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__ Objective __** <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Estimate how much electrical energy you consume on a daily basis (ie: what does it cost my parents)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__ What to do? __**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">1. Identify 10 electrical appliances you use on a daily basis and identify their power rating (in Watts). <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">2. Determine the total kWh (kilowatt-hours) of power that you consume with these ten appliances. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;"> Sample Calculations <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Crock pot-.15 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Toaster-1.5 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Keurig-1.5 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Blow-dryer- 2 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Can opener- .168 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Pencil sharpener- .144 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Blender- .72 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Magic bullet- .205 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Coffee grinder- .13 KW
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Waffle maker- .1 KW

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;"> 4. Look at your household electric bill. Find two numbers: <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;"> 5. Costs of Electricity. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;"> >> Actual cost per kWh=11.9 cents per kWh >> 2.79843 x .119 = $0.33 >> Cost per month: 0.33 x 30 = $9.99 <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">**__ Evaluate __** <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">1. Does the cost of electricity seem like a lot to you? Discuss this with your friends. <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">2. Keep in mind that this cost only reflects ten appliances. What do you think your total cost actually is? Are there major appliances that you may have excluded from your list of ten that would make a big difference <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">3. If you think your consumption is a lot – what can you change? Do you need/should change? <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">I think that the electric bill is overpriced. When I discussed wit my family we all agreed that we need to make a more conscious effort to conserve energy. We realized that it is especially hard for those who have big families, who are constantly maximizing the amount of electricity used, but now that we are only three people we no longer have that excuse. Also, when children are younger, I feel like there are more lights on in the house and more use of electrical appliances. In the end I learned that most people, including myself, underestimate and overlook how much each appliance costs, because they are uneducated.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">the total dollar amount due
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">$265.75
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">kWh consumed that month.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">1426 kWh
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Calculate the average cost per kWh
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The number above includes delivery
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">You can also look this value up on the bill itself.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">$0.119
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Compare the two values. Why are they different?
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Probably because PSE&G wants to make a profit.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">Multiply the kWh you use per day by the cost per kWh to determine what you cost your parents.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 10pt;">2.79843*0.119=$0.333
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">When discussing the cost it does not seem like a lot of money at all, however, when repeated each day, the cost of all these appliances definitely adds up. There are so many appliances that I did not account for so I’m sure that it is also much more than it appears.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">I left out refrigerator, washer machine, dryer, microwaves, televisions, computers, etc. I am sure it costs much more than this. Including these items would greatly affect my data.
 * <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">One of the many things I should do is shut off the lights in my room and closet. There are a lot of days where I forget and they could be on without anyone noticing for a decent amount of time. Also I never unplug any of my chargers such as my computer and cell phone chargers. I have been getting better at shutting off the lights, but I definitely need to remember to unplug everything when I am finished.