1. Work, Power, and Modes of Energy
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Work, Power, and Modes of Energy
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. If work is scalar, can it be negative?
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Work
Scalar quantity defined as the product of the force applied to an object and the displacement of the object.
W=Fd
Units for work is Joules
J=N·m
If work is scalar, can it be negative?
When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object. There are 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. There are several good examples of work that can be observed in everyday life - a horse pulling a plow through the field, a father pushing a grocery cart down the aisle of a grocery store, a freshman lifting a backpack full of books upon her shoulder, a weightlifter lifting a barbell above his head, an Olympian launching the shot-put, etc. In each case described here there is a force exerted upon an object to cause that object to be displaced.
Yes, if the Force acting on the object is in the opposite direction of the object’s motion then work will be negative.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

3. Identify the following as work/non-work.
A book falls off a table and free falls to the ground.
A teacher pushing on a brick wall.
A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. (Careful!)
A teacher pushing on a brick wall. This is not an example of work. The wall is not displaced. A force must cause a displacement in order for work to be done.
A book falls off a table and free falls to the ground. This is an example of work. There is a force (gravity) which acts on the book which causes it to be displaced in a downward direction (i.e., "fall").
A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. This is not an example of work. There is a force (the waiter pushes up on the tray) and there is a displacement (the tray is moved horizontally across the room). Yet the force does not cause the displacement. To cause a displacement, there must be a component of force in the direction of the displacement.
A rocket accelerates through space.

4. Calculating Work
A 10-N force is applied to push a block across a friction free surface for a displacement of 5.0 m to the right.
W=Fd
W=(10N)(5.0m)
W=50J
A force of 50 N acts on the block to move the block a horizontal distance of 3.0 m. How much work is done by the applied force?

5. Graphing Work L x W = 2 m x 25 N =
Force vs Displacement
L x W =
2 m x 25 N =
50 N·m = 50 J
If a 25 N force is applied to an object for 2 meters, how much work is done on the object?
W = Fd =
(25N)(2m) =
50 J
What is the area under the graph at right?

6. Power The rate at which work is done. (Work/Time) P=W/t P=(Fd)/t P=Fv
Metric unit for power is Watts
Watts = J/s
(1000 Watts = 1 kW)
English unit for power is horsepower (Hp)
1 Hp=746 W
Two physics students, Will N. Andable and Ben Pumpiniron, are in the weightlifting room. Will lifts the 100-pound barbell over his head 10 times in one minute; Ben lifts the 100-pound barbell over his head 10 times in 10 seconds. Which student does the most work?
Work has nothing to do with the amount of time that this force acts to cause the displacement. Sometimes, the work is done very quickly and other times the work is done rather slowly. For example, a rock climber takes an abnormally long time to elevate her body up a few meters along the side of a cliff. On the other hand, a trail hiker (who selects the easier path up the mountain) might elevate her body a few meters in a short amount of time. The two people might do the same amount of work, yet the hiker does the work in considerably less time than the rock climber. The quantity that has to do with the rate at which a certain amount of work is done is known as the power. The hiker has a greater power rating than the rock climber.
Power is the rate at which work is done. It is the work/time ratio.
All three equations represent the same thing, just substituting in the work formula.

7. Energy is kinda like a substance:
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What is Energy (E)?
The ability to do work in a system.
Changes in:
Temperature
Motion
Shape
System: object(s) we focus on in a problem.
Surroundings: everything else!
Energy is kinda like a substance:
You can measure it. (Joules, calories, BTUs)
It can be stored in a variety of ways.
It can be transferred.
It is universal.
Energy is all around us, in everything that we touch and see. Even in the molecules in the air. However, energy is very difficult to define. There are many forms of energy, and since it can be transferred it can change form. Even though it is difficult to define what energy is, we can still work to understand the various forms of energy and how it can influence objects.
When we say that energy has the “ability” to produce change, we mean that it can, not that it will. This is an important distinction if you are to understand how energy works in a system.
Energy behaves a bit like a substance….although it’s not really a substance. This makes it easier to be able think, talk, and evaluate energy.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

8. Kinetic Energy (K) “moving” energy Dependent on m and v
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Kinetic Energy (K)
“moving” energy
Anything in motion has KE
Wind
Rain
Cars
People
Dependent on m and v
But….velocity has more of an effect than mass.
Kinetic literally means moving in Latin. Any object that is not at rest is going to have some amount of kinetic energy. The amount of Kinetic energy is dependent on the mass and velocity of an object, but velocity has more effect than the mass does.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

9. Gravitational Potential Energy (UG) Elastic Potential Energy (US)
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Potential Energy (U)
Energy because of position.
Several Types:
Gravitational Potential Energy (UG)
Energy due to Fg.
Comes from mass, height, and g.
The higher off the ground, the more UG.
No height, No UG.
Elastic Potential Energy (US)
Energy due to stretching or compression.
Often transferred to other objects causing them to move.
WHERE an object is can effect the amount of energy that it has. The position of an object can give it the “potential” energy.
Gravitational Potential Energy is energy that is stored in the gravitational pull on objects. Consider a waterfall, for example. The higher up the edge of the falls, the harder the water hits the pool surface below. That’s why sliding off Niagra would kill you, but a tiny dip in the river is fun to ride on a tube. The farther something is from the earth the more energy it has stored up…the more is stored the more Kinetic it will have once it starts moving.
Elastic Potential Energy can be held in compressed or stretched objects. Rubber bands, bungee cords, springs, trampolines, balls…etc. The farther you pull back a rubber band to snap someone with the more it hurts, the more pressure applied to a spring the farther it will snap back….the harder you jump on a trampoline the farther you will fly.
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

10. Chemical Potential Energy
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Chemical Potential Energy
Energy stored in the chemical bonds of atoms.
Food
Batteries
Wood
Fuel
If it can undergo a chemical change then it has PEchem
© 2007 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

11. Where does all that energy go?
Dissipated Energy
Energy that produces random movement of molecules, light, or sound.
Usually due to friction or deformation of objects.
Non-reusable form of energy.
Where does all that energy go?
Think about the sound the crash from this image must have made. All the energy that it takes to make that sound has to go somewhere right? Remember that energy is never destroyed, but in this instance it is also non-reusable.
When energy is dissipated it is lost in the form of heat. Like when you rub your hands together or tap your foot repeatedly on the floor. These both cause surfaces and molecules to heat up and therefore move around. That extra energy is lost as heat.