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Summary of Chapter 6 Lesson 1a 1/12/12 (method 1)
When a force acts upon an object to cause a displacement of the object, it is said that ** work ** was done upon the object. three key // ingredients // to work - force, displacement, and cause. In order for a force to qualify as having done // work // on an object, there must be a displacement and the force must // cause // the displacement. W=(F)(d)(costheta) On occasion, a force acts upon a moving object to hinder a displacement. In such instances, the force acts in the direction opposite the objects motion in order to slow it down. The force doesn't cause the displacement but rather // hinders // it. These situations involve what is commonly called // negative work //. The // negative // of negative work refers to the numerical value that results when values of F, d and theta are substituted into the work equation. Since the force vector is directly opposite the displacement vector, theta is 180 degrees. The cosine(180 degrees) is -1 and so a negative value results for the amount of work done upon the object. Units of work – Joule (J) One Joule is equivalent to one Newton of force causing a displacement of one meter. When a force acts to cause an object to be displaced, three quantities must be known in order to calculate the work. three quantities: force, displacement, and the angle between the force and the displacement. work = (force)(displacement)(costheta) where // theta // is the angle between the force and the displacement vectors.
 * Definition of mathematics of work**
 * Calculating the amount of work done by forces**

Summary of Chapter 6 Lesson 2 1/30/12 (method 1)
there are certain types of forces, that when present and when involved in doing work on objects will change the total mechanical energy of the object. 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 (or vice versa). The two categories of forces are referred to as internal forces and external forces.
 * Internal vs 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. **

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 (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. This is referred to as [|energy conservation and will be discussed in detail later in this lesson]. 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 **.

1. PE to KE

2. PE to KE

3. KE to PE

4. KE to PE

5. PE to KE

1. + KE 2. + both 3. + KE 4. - KE 5. + KE

Power Costs Activity



 * Sample Formulas**

With the ten appliances listed, I cost my parents about $0.21 a day. This value does not seem like it is that much, but over time, it can add up. Additionally, this is not taking other appliances into account, such as chargers, lightbulbs, other TV's and computers, and larger things such as the refrigerator. After considering all of this, I realize that there are things I can do to help decrease the cost of our electricity bill. I can turn the lights off when I leave a room and unplug chargers when they are not in use. Even with taking everything into account, I do not think I cost my parents too much considering how much we pay and that there are many other people in my family that contribute to the electric bill as well.