Ch6_Doomank

Chapter 6 toc

**Part A**:
WORK:
 * Definition and Mathematics of Work **
 * When a force acts upon an object to cause a displacement of the object, it is said that **work**  was done upon the object.
 * 1) force
 * 2) displacement
 * 3) cause
 * For a force to qualify as having done //work// on an object, there must be a displacement and the force must //cause// the displacement.
 * ex. - a horse pulling a plow through the field

//**Work Equation: **// //**w=F*d*[cos(theta)] **//

 **The Meaning of Negative Work** **The Joule is the unit of work.****1 Joule = 1 Newton * 1 meter****1 J = 1 N * m**
 * <span style="font-family: 'Comic Sans MS',cursive;">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.
 * <span style="font-family: 'Comic Sans MS',cursive;">Theta is 180 degrees for negative work.

<span style="display: block; font-family: 'Comic Sans MS',cursive; text-align: left;">**Part B**:
 * <span style="color: #000000; font-family: 'Comic Sans MS',cursive; font-size: 14px; text-align: left;">Calculating the Amount of Work Done by Forces ** three quantities must be known in order to calculate the work.
 * <span style="font-family: 'Comic Sans MS',cursive;">force
 * <span style="font-family: 'Comic Sans MS',cursive;">displacement
 * <span style="font-family: 'Comic Sans MS',cursive;">the angle between the force and the displacement (theta)
 * <span style="font-family: 'Comic Sans MS',cursive;">Actual Equation :
 * <span style="font-family: 'Comic Sans MS',cursive;">Work= force•displacement•cosine(theta)


 * Lesson 2a**

Internal vs. External Forces
All the types of forces could be categorized as:
 * contact forces
 * action-at-a-distance forces.
 * action-at-a-distance force is when objects are not physically touching.

 >
 * 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
 * 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**.
 * **external forces**
 * include the applied force, normal force, tension force, friction force, and air resistance force. And for our purposes, the
 * **internal forces**
 * include the gravity forces, magnetic force, electrical force, and spring force. While this is a simplistic approach, it is an approach that will serve us well in our introduction to physics.


 * < **Internal Forces** ||< **External Forces** ||
 * < **Fgrav** **Fspring** ||< **Fapp** **Ffrict** **Fair** **Ftens** **Fnorm** ||

. . 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.
 * 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**