Ch6_WeissB

=__Chapter 6__= toc

Summarization (Method 4) of Work, Energy, and Power Lesson 1a
What is work? A way of analyzing motion by seeing how the energy of a object is affected. When a force acts upon an object to cause a displacement of the object, it is said that work is done on that object. There are three key ingredients to work: force, displacement, and cause

How is work calculated? Work is calculated through the equation W= f x d x cosΘ. F is force, d is displacement, and Θ is the angle between the force vector and the displacement vector.

What is the meaning of negative work? Negative work occurs when the force actually hinders displacement (this is when theta is 180º).

What are the units of work? Work is measured in joules.

Summarization (Method 1) of Work, Energy, and Power Lesson 2a
There are a variety of ways to categorize all the types of forces. One way is to categorize forces based upon whether or not their presence is capable of changing an object's total mechanical energy. There are certain types of forces, that when present and when involved in doing work on objects, that can 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. 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, but if it 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. These forces 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. This means that when potential energy decreases, kinetic energy increase, and vice versa. The sum of kinetic and potential energy remains constant. This is referred to as energy conservation. Internal forces are sometimes referred to as conservative forces.

Sample Problems on Work, Energy, and Power Lesson 2a
For the first 5 problems, I got 5/5 right.

For the next 6 problems, I got 5/6 right. The one I got wrong was #2, when I answered that the baseball would only have change in kinetic energy when it also had change in potential energy as well.