Ch6_BehrensB


 * Chapter 6toc**

= Work, Energy and Power - Lesson 2; a = = __ **Internal vs. External Forces** __ = **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.

. Note that in the five situations described above, a horizontal force can never change the potential energy of an object. Horizontal forces cannot cause vertical displacements. The only means by which an external or nonconservative force can contribute to a potential energy change is if the force has a vertical component. Potential energy changes are the result of height changes and __only__ a force with a vertical component can cause a height change.
 * < **Internal Forces** ||< **External Forces** ||
 * < **Fgrav** **Fspring** ||< **Fapp** **Ffrict** **Fair** **Ftens** **Fnorm** ||
 * 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.
 * Under such circumstances, 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**
 * When the only type of force doing net work upon an object is an internal force (for example, gravitational and spring forces), the __ [|total mechanical energy (KE + PE)] __ 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**

= **Power Costs Activity** = Estimate how much electrical energy you consume on a daily basis (ie: what does it cost my parents)
 * __ Objective __**

Data Table: Sample Calculations:
 * 1) Look at your household electric bill. Find two numbers:
 * 2) the total dollar amount due
 * $185.64
 * 1) kWh consumed that month.
 * 1170kWh

. The cost per kWh stated on the electric bill and the calculated value shown above are the same.
 * 1) Costs of Electricity. Calculate the average cost per kWh by dividing the dollar amount by the kWh consumed. This is approximately what each kWh costs your family. (Note: this figure includes fees and taxes, too). The cost will probably be between $0.10-$0.20 per kWh – depending on how much electricity you use. Electricity costs more if you exceed a certain usage
 * 1) Compare the two values. Why are they different?
 * 1) Multiply the kWh you use per day by the cost per kWh to determine what you cost your parents.

After calculating my average cost based on nine appliances I use daily, the cost of electricity does not seem like a lot. However, with the addition of other electrical house hold items that are used, such as the refrigerator and even the lights of other rooms, as well as the electricity used by the other members of my family, the bill reflects the amount of kWh actually consumed. The cost of electricity seems relatively fair considering the amount that is needed to support one household. My average cost for the entire month is within range of $16.50, as calculated above. Overall my family shares equally in the usage of our electricity. For example, major appliances, such as the refrigerator, microwave, the Cablevision box, and the home computer, which are constantly plugged into an outlet, consume considerable amounts of electricity on a daily basis. Also, the other members of my family use the bathroom lights and their own bedroom lights which adds to the total cost. The minor appliances, such as multiple laptop charges, battery chargers, and household radios contribute to the electric bill too. Personally, I do not feel that my consumption is too great that a change in my daily routine is necessary. However, minute details throughout the day-- turning of lights upon exiting a room, for example-- can subtract any range of cost from the total bill. If each member of the family paid attention to these actions then the cost might be reduced by a substantial amount.
 * __ Evaluate __**
 * 1) Does the cost of electricity seem like a lot to you? Discuss this with your friends.
 * 1) 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?
 * 1) If you think your consumption is a lot – what can you change? Do you need/should change?

This activity put into perspective, for me, my usage of electricity on a daily basis. Also, I saw for the first time what my family's monthly electric bill looks like, the amount we all use, and the cost of our contributions. What originally seemed like a large cost for electricity became understandable after calculating my daily kWh based on nine personal appliances. Upon brainstorming which appliances I would include in this activity, I contemplated the amount of electricity I use everyday, and I concluded that it seemed like a lot. However, with the total amount per day coming to about 5.6 kWh, and the entire bill charged for 1170 kWh, I only personally added 0.5% per day and 14.4% per month of electricity. Without service charges, the cost of 1170 kWh is $114.43 -- a small amount considering the amount of electricity we use daily! Overall, I think this activity was successful in opening my eyes towards conserving electricity and managing my usage of kWh.