1. Thursday(10/07): The Concept of Work in Physics, the Dot Product,

and Area Under a Curve. HW: Read pages 181-193 and solve prob. 3, 7, 8,

12, and 19 on pages 209-211.

2. Friday(10/08): Kinetic Energy, Conservation of Energy, and Power.

HW: Read pages 193-208 and solve prob. 25, 31, 37, and 39 on pages

211-212.

3. Monday(10/11): (Dress Caveman)Potential Energy, Conservation of

Mechanical Energy, and Conservative/Non-Conservative Forces. HW: Read

pages 217-229 and solve prob. 2, 3, 6, 10, 11, and 17 on pages 143-144.

4. Tuesday(10/12): (Dress Greek/Toga)Lab experiment on The Inclined

Plane. HW: Complete lab report and write Abstract, due Monday.

5. Wednesday(10/13): (Dress Cowboy/Western)Relationship Between

Conservative Forces and Potential Energy. HW: Read pages 229-239 and

solve prob. 24, 27, 31, 42, and 44 on pages 243-245.

6. Thursday(10/14): (Dress '60's/Hippie)Chapter 7 & 8 Review I.

HW: Finish all review handouts.

7. Monday(10/18): Chapter 7 & 8 Review II. HW: Finish all review

handouts.

8. Tuesday(10/19):TEST on Ch.7 & 8 - Energy and Energy Transfer,

and Potential Energy. HW: Go to Website for notes on Ch.9 - Linear

Momentum and Collisions.

Very Important: If you have any questions or miss a class, see

1. Work is done in physics when a force is applied to an object and it

undergoes a displacement in the direction of the force.

2. This definition allows us to calculate Work = Force x Displacement or

W = F·Δx ,and then it is measured in Newton meters, Nm, or Joules.

3. Work is a scalar quantity, even though Force and Displacement are vectors,

and can be computed as a Dot-Product of the two vectors.

4. This unit was named after James Prescott Joule (1818-1889), the Scottish

physicist who determined a method to perform mechanical work with heat.

5. We usually do work against friction when sliding an object, and against

gravity when lifting, W = mgΔy.

6. When applying a force at an angle, we use the cosine of the angle to

compute the amount of work done, W =(Fcosθ)Δx.

7. Energy is the ability to do work, and there are two kinds of energy, kinetic

and potential.

8. Kinetic energy is due to mass and velocity, K = ½mv² .

9. Potential energy is due to an objects position, U_GRAV = mgΔy ,

hence, gravitational potential energy.

10. Potential energy can also be elastic, U_ELAS = ½kx² , with k being the

spring constant.

11. Work can also be computed by finding the area under a Force vs

Displacement curve. This also means that we can use Integral Calculus to

calculate Work, W = ∫F(x) dx.

12. Work can also be explained as the transfer of energy by mechanical

means. Mechanical energy is the total kinetic and potential energy present

in a given situation.

13. There is a conservation law for energy which states that "energy can

change in form but can never be created or destroyed", or K_i + U_i = K_f + U_f.

14. Neglecting friction, mechanical energy is conserved, so that the total

amount remains constant.

15. The net work done on or by an object is equal to the change in the

kinetic energy of that object. This means that W = ΔK = K_f - K_i .

16. Power is the rate of doing work, P = W/t , or P = F·Δx/t , or even

P = F·v_avg , and is measured in Watts.

17. The Watt was named after James Watt (1736-1819) from Scotland, who

perfected the steam engine and made it practical to use.

18. Power is also the rate at which energy is transferred, with 1000 watts

being, of course, a kilowatt, kw.

19. Machines with the same power ratings in watts do the same amount of

work in different time intervals.

20. There are six simple machines: pulley, inclined plane, wheel and axle,

jackscrew, lever, and wedge. Each has a Mechanical Advantage, Ideal

Mechanical Advantage, Work Output, Work Input, and an Efficiency. We will

derive the equations for these in class.

WEBSITE NOTES: Ch. 8 - Potential Energy.

Some important concepts to remember from the previous discussion are :

(i) the energy associated with the motion of an object is kinetic energy,

K = ½mv² .

(ii) potential energy is associated with the position or configuration of an

object.

(iii) potential energy can be thought of as stored energy that can be

converted to kinetic energy or other forms of energy.

(iv) in working problems involving gravitational potential energy, it is always

necessary to set the gravitational potential energy equal to zero at some

location.

(v) the choice of the zero level is arbitrary, because the important quantity is

the difference in potential energy.

(vi) it is often convenient to use the surface of the Earth as the zero

potential level, or some other level relevant to a particular problem.

Now for the new concepts given in Chapter 8 of Physics For Scientists and

Engineers:

1. The gravitational potential energy of a particle of mass m that is elevated

a distance y near the Earth's is U = mgy . This is the same as the amount of

work done in lifting the object.

2. The elastic potential energy stored in a spring of force constant k is

U = ½kx² . This is also the same amount of work done in compressing the

spring a distance x .

3. A force is conservative if the work it does on a particle is independent of

the path the particle takes between the two points. This means that it

doesn't matter how you lift an object.

4. Another way to say this is, a force is conservative if the work it does is

zero when the particle moves through an arbitrary closed path and returns

to its original position. So if you lift an object and put it back down, then

no work is done.

5. A force that does not meet any of the above described criteria is non-

conservative, or sometimes called, dissipative. A force of this type is

friction.

6. A potential energy function U can be associated only with a conservative

force.

7. If a conservative force F acts on a particle that moves along the x axis

from x₁ to x₂ , the change in the potential energy of the particle equals the

negative of the work done by the force.

8. Mathematically, this means that the change in the potential energy would

be the negative of the Integral, ∫F(x) dx from x₁ to x₂.

9. The total mechanical energy of a system is defined as the sum of the

kinetic energy and potential energy or, E = K + U.

10. If no external forces do work on a system, and there are no non-

conservative forces, the total mechanical energy of the system is constant

or , K_i + U_i = K_f + U_f . This is a statement of the Law of Conservation of

Energy.

11. The change in total mechanical energy of a system equals the change

in the kinetic energy due to internal non-conservative forces plus the change

 in kinetic energy due to all external forces.

12. Internal or external forces can either increase or decrease the kinetic

energy of a system.

Make sure you use  these steps to solve any problem in Physics:

(i) read the problem and identify the given variables

(ii) determine what you are asked to solve for

(iii) find the correct vector formula to use

(iv) use Algebra, Trigonometry, and/or Calculus to isolate the unknown

(v) substitute-in the given information and simplify.