Ch6_Weinfeld

= toc = = = =Internal vs. External Forces=

There are a variety of ways to categorize all the types of forces. And there are other types of forces that can never change the total mechanical energy of an object, but rather can only transform the energy of an object from potential energy to kinetic energy. The two categories of forces are referred to as internal forces and external forces. Forces can be categorized as internal forces or external forces. External forces include the applied force, normal force, tension force, friction force, and air resistance force. The internal forces include the gravity forces, magnetic force, electrical force, and spring force. The importance of categorizing a force as being either internal or external is related to the ability of that type of force to change an object's total mechanical energy when it does work upon an object. 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. 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 the [|__total mechanical energy (KE + PE)__] of that object remains constant. In such cases, the object's energy changes form. This is referred to as energy conservation. 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.

For the activities, I got all of the first five right! For the second part, I got the first part of each question correct, but I got two about the change of PE or KE or both wrong because I picked just one instead of realizing that it was both.

Energy Activity

 * Why Do My Parents Tell Me to Turn off the Lights? **** J **


 * __ Objective __**

Estimate how much electrical energy you consume on a daily basis (ie: what does it cost my parents)


 * __ What to do? __**


 * 1) Identify 10 electrical appliances you use on a daily basis and identify their power rating (in Watts).


 * Hair dryer: 1875 W
 * Microwave: 1450 W
 * Toaster Oven: 1400 W
 * Clock Radio: 10 W
 * Water Cooler: 960 W
 * Desktop Computer: 250 W
 * Flat Iron: 20 W
 * Laptop Charger: 438 W
 * Fridge: 725 W
 * iPhone Charger: 10 W


 * 1) The power rating will be listed on the info label – typically on the back of or under the appliance. Often the power consumption is listed in terms of AMPERAGE (amperage measures the current of electricity consumed). The power rating (in Watts) may be calculated using the following formula:

Power (in Watts) = AMPS x 120 volts.

For example, a 12 AMP vacuum cleaner uses 12A x 120v = 1440 Watts of power.


 * 1) Determine the total kWh (kilowatt-hours) of power that you consume with these ten appliances.


 * First estimate how many hours you use each appliance. For example, you may use your hairdryer every second day for 10 minutes – so on average you use it for 0.17h/d ¸ 2 = 0.085 h per day.


 * Calculate the kWh used per day by multiplying the wattage of the appliance by the hours used (per day).


 * Finally, determine the total kWh you use per day.

4. What does this cost your parents? 5. Look at your household electric bill. Find two numbers: 6. Costs of Electricity 7. Multiply the kWh you use per day by the cost per kWh to determine what you cost your parents. 8. Does the cost of the electricity seem like a lot to you? Discuss this with your friends. 9. Keep in mind that the cost only reflects 10 appliances. What do you think your total cost actually is? Are there major appliances that hyou may have excluded from your list of ten that would make a big difference? 10. If you think your consumption is a lot - what can you change?Do you need/should change?
 * $0.11 * $52.4068 = $4.99
 * the total dollar amount
 * $195.56
 * kWh consumed that month
 * 1,732 kWh
 * 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.
 * average cost per kWh = $/kWh = $0.11
 * you can also look this value up on the bill itself
 * $0.18
 * compare the two values. why are they different?
 * the number on the bill includes a delivery charge and PSE&G probably makes it more expensive so that they can receive a profit.
 * 52.4068 kWh X $0.11 = $5.76
 * Yes, it does seem like a lot. Even though the number doesn’t look that big, it clearly adds up quickly. I never really take the time to think about how we are paying for all of the electricity we use by the minute. Now that I realize the cost of using electricity, I will be more mindful when it comes to turning things off.
 * Yes, the cost is probably much bigger. I did include some of the big items, like the refrigerator and water cooler for example. However, we also have our televisions, washing machine, and dry cleaner.
 * I can’t change the fact that our fridge is plugged in twenty four seven. However, I can lessen the amount of time I charge my phone and laptop and I can also use less time doing my hair or heating up food. My dad has gotten me into the habit of turning off lights and tv when I leave a room, so I think I am up to a good start.

I found this assignment very interesting. I have never looked at my family’s electricity bill and I think that this was a good wake up call. When I use electricity, I do not realize that my family has to pay for it. I never used to understand why my dad cared when we left the lights on after we left a room. Though I have begun to get in better habits, I still didn’t realize the depth of the situation. However, the few dollars I calculated to cost my family a day can quickly add up and there is certainly a lot more electricity used in my home. Overall, I think that the project made me more knowledgeable and conscientious of my energy consumption.